_docs_en.utf8.txt

@advanced_1000_h1
Advanced Topics

@advanced_1001_a
Result Sets

@advanced_1002_a
Large Objects

@advanced_1003_a
Linked Tables

@advanced_1004_a
Transaction Isolation

@advanced_1005_a
Multi-Version Concurrency Control (MVCC)

@advanced_1006_a
Clustering / High Availability

@advanced_1007_a
Two Phase Commit

@advanced_1008_a
Compatibility

@advanced_1009_a
Standards Compliance

@advanced_1010_a
Run as Windows Service

@advanced_1011_a
ODBC Driver

@advanced_1012_a
Using H2 in Microsoft .NET

@advanced_1013_a
ACID

@advanced_1014_a
Durability Problems

@advanced_1015_a
Using the Recover Tool

@advanced_1016_a
File Locking Protocols

@advanced_1017_a
Protection against SQL Injection

@advanced_1018_a
Restricting Class Loading and Usage

@advanced_1019_a
Security Protocols

@advanced_1020_a
SSL/TLS Connections

@advanced_1021_a
Universally Unique Identifiers (UUID)

@advanced_1022_a
Settings Read from System Properties

@advanced_1023_a
Setting the Server Bind Address

@advanced_1024_a
Limitations

@advanced_1025_a
Glossary and Links

@advanced_1026_h2
Result Sets

@advanced_1027_h3
Limiting the Number of Rows

@advanced_1028_p
Before the result is returned to the application, all rows are read by the database. Server side cursors are not supported currently. If only the first few rows are interesting for the application, then the result set size should be limited to improve the performance. This can be done using LIMIT in a query (example: SELECT * FROM TEST LIMIT 100), or by using Statement.setMaxRows(max).

@advanced_1029_h3
Large Result Sets and External Sorting

@advanced_1030_p
For large result set, the result is buffered to disk. The threshold can be defined using the statement SET MAX_MEMORY_ROWS. If ORDER BY is used, the sorting is done using an external sort algorithm. In this case, each block of rows is sorted using quick sort, then written to disk; when reading the data, the blocks are merged together.

@advanced_1031_h2
Large Objects

@advanced_1032_h3
Storing and Reading Large Objects

@advanced_1033_p
If it is possible that the objects don't fit into memory, then the data type CLOB (for textual data) or BLOB (for binary data) should be used. For these data types, the objects are not fully read into memory, by using streams. To store a BLOB, use PreparedStatement.setBinaryStream. To store a CLOB, use PreparedStatement.setCharacterStream. To read a BLOB, use ResultSet.getBinaryStream, and to read a CLOB, use ResultSet.getCharacterStream. When using the client/server mode, large BLOB and CLOB data is stored in a temporary file on the client side.

@advanced_1034_h2
Linked Tables

@advanced_1035_p
This database supports linked tables, which means tables that don't exist in the current database but are just links to another database. To create such a link, use the CREATE LINKED TABLE statement:

@advanced_1036_p
You can then access the table in the usual way. Whenever the linked table is accessed, the database issues specific queries over JDBC. Using the example above, if you issue the query <code>SELECT * FROM LINK WHERE ID=1</code> , then the following query is run against the PostgreSQL database: <code>SELECT * FROM TEST WHERE ID=?</code> . The same happens for insert and update statements. Only simple statements are executed against the target database, that means no joins. Prepared statements are used where possible.

@advanced_1037_p
To view the statements that are executed against the target table, set the trace level to 3.

@advanced_1038_p
There is a restriction: When inserting into a linked table, and when updating a linked table, NULL and values that are not set are both inserted as NULL. This may not have the desired effect if the default value for this column in the target table is not NULL.

@advanced_1039_p
If multiple linked tables point to the same database (using the same database URL), the connection is shared. To disable this, set the system property h2.shareLinkedConnections to false.

@advanced_1040_p
The CREATE LINKED TABLE statement supports an optional schema name parameter. See the grammar for details.

@advanced_1041_h2
Transaction Isolation

@advanced_1042_p
This database supports the following transaction isolation levels:

@advanced_1043_b
Read Committed

@advanced_1044_li
This is the default level.  Read locks are released immediately.  Higher concurrency is possible when using this level.

@advanced_1045_li
To enable, execute the SQL statement    'SET LOCK_MODE 3'

@advanced_1046_li
or append ;LOCK_MODE=3 to the database URL: jdbc:h2:~/test;LOCK_MODE=3

@advanced_1047_b
Serializable

@advanced_1048_li
To enable, execute the SQL statement    'SET LOCK_MODE 1'

@advanced_1049_li
or append ;LOCK_MODE=1 to the database URL: jdbc:h2:~/test;LOCK_MODE=1

@advanced_1050_b
Read Uncommitted

@advanced_1051_li
This level means that transaction isolation is disabled.

@advanced_1052_li
To enable, execute the SQL statement    'SET LOCK_MODE 0'

@advanced_1053_li
or append ;LOCK_MODE=0 to the database URL: jdbc:h2:~/test;LOCK_MODE=0

@advanced_1054_p
When using the isolation level 'serializable', dirty reads, non-repeatable reads, and phantom reads are prohibited.

@advanced_1055_b
Dirty Reads

@advanced_1056_li
Means a connection can read uncommitted changes made by another connection.

@advanced_1057_li
Possible with: read uncommitted

@advanced_1058_b
Non-Repeatable Reads

@advanced_1059_li
A connection reads a row, another connection changes a row and commits,  and the first connection re-reads the same row and gets the new result.

@advanced_1060_li
Possible with: read uncommitted, read committed

@advanced_1061_b
Phantom Reads

@advanced_1062_li
A connection reads a set of rows using a condition, another connection  inserts a row that falls in this condition and commits, then the first connection  re-reads using the same condition and gets the new row.

@advanced_1063_li
Possible with: read uncommitted, read committed

@advanced_1064_h3
Table Level Locking

@advanced_1065_p
The database allows multiple concurrent connections to the same database. To make sure all connections only see consistent data, table level locking is used by default. This mechanism does not allow high concurrency, but is very fast. Shared locks and exclusive locks are supported. Before reading from a table, the database tries to add a shared lock to the table (this is only possible if there is no exclusive lock on the object by another connection). If the shared lock is added successfully, the table can be read. It is allowed that other connections also have a shared lock on the same object. If a connection wants to write to a table (update or delete a row), an exclusive lock is required. To get the exclusive lock, other connection must not have any locks on the object. After the connection commits, all locks are released. This database keeps all locks in memory.

@advanced_1066_h3
Lock Timeout

@advanced_1067_p
If a connection cannot get a lock on an object, the connection waits for some amount of time (the lock timeout). During this time, hopefully the connection holding the lock commits and it is then possible to get the lock. If this is not possible because the other connection does not release the lock for some time, the unsuccessful connection will get a lock timeout exception. The lock timeout can be set individually for each connection.

@advanced_1068_h2
Multi-Version Concurrency Control (MVCC)

@advanced_1069_p
The MVCC feature allows higher concurrency than using (table level or row level) locks. When using MVCC in this database, delete, insert and update operations will only issue a shared lock on the table. An exclusive lock is still used when adding or removing columns, when dropping the table, and when using SELECT ... FOR UPDATE. Connections only 'see' committed data, and own changes. That means, if connection A updates a row but doesn't commit this change yet, connection B will see the old value. Only when the change is committed, the new value is visible by other connections (read committed). If multiple connections concurrently try to update the same row, this database fails fast: a concurrent update exception is thrown.

@advanced_1070_p
To use the MVCC feature, append MVCC=TRUE to the database URL:

@advanced_1071_p
MVCC can not be used at the same time as MULTI_THREADED. The MVCC feature is not fully tested yet.

@advanced_1072_h2
Clustering / High Availability

@advanced_1073_p
This database supports a simple clustering / high availability mechanism. The architecture is: two database servers run on two different computers, and on both computers is a copy of the same database. If both servers run, each database operation is executed on both computers. If one server fails (power, hardware or network failure), the other server can still continue to work. From this point on, the operations will be executed only on one server until the other server is back up.

@advanced_1074_p
Clustering can only be used in the server mode (the embedded mode does not support clustering). It is possible to restore the cluster without stopping the server, however it is critical that no other application is changing the data in the first database while the second database is restored, so restoring the cluster is currently a manual process.

@advanced_1075_p
To initialize the cluster, use the following steps:

@advanced_1076_li
Create a database

@advanced_1077_li
Use the CreateCluster tool to copy the database to another location and initialize the clustering.  Afterwards, you have two databases containing the same data.

@advanced_1078_li
Start two servers (one for each copy of the database)

@advanced_1079_li
You are now ready to connect to the databases with the client application(s)

@advanced_1080_h3
Using the CreateCluster Tool

@advanced_1081_p
To understand how clustering works, please try out the following example. In this example, the two databases reside on the same computer, but usually, the databases will be on different servers.

@advanced_1082_li
Create two directories: server1 and server2.  Each directory will simulate a directory on a computer.

@advanced_1083_li
Start a TCP server pointing to the first directory.  You can do this using the command line:

@advanced_1084_li
Start a second TCP server pointing to the second directory.  This will simulate a server running on a second (redundant) computer.  You can do this using the command line:

@advanced_1085_li
Use the CreateCluster tool to initialize clustering.  This will automatically create a new, empty database if it does not exist.  Run the tool on the command line:

@advanced_1086_li
You can now connect to the databases using an application or the H2 Console using the JDBC URL jdbc:h2:tcp://localhost:9101,localhost:9102/~/test

@advanced_1087_li
If you stop a server (by killing the process), you will notice that the other machine continues to work, and therefore the database is still accessible.

@advanced_1088_li
To restore the cluster, you first need to delete the database that failed, then restart the server that was stopped, and re-run the CreateCluster tool.

@advanced_1089_h3
Clustering Algorithm and Limitations

@advanced_1090_p
Read-only queries are only executed against the first cluster node, but all other statements are executed against all nodes. There is currently no load balancing made to avoid problems with transactions. The following functions may yield different results on different cluster nodes and must be executed with care: RANDOM_UUID(), SECURE_RAND(), SESSION_ID(), MEMORY_FREE(), MEMORY_USED(), CSVREAD(), CSVWRITE(), RAND() [when not using a seed]. Those functions should not be used directly in modifying statements (for example INSERT, UPDATE, or MERGE). However, they can be used in read-only statements and the result can then be used for modifying statements.

@advanced_1091_h2
Two Phase Commit

@advanced_1092_p
The two phase commit protocol is supported. 2-phase-commit works as follows:

@advanced_1093_li
Autocommit needs to be switched off

@advanced_1094_li
A transaction is started, for example by inserting a row

@advanced_1095_li
The transaction is marked 'prepared' by executing the SQL statement <code>PREPARE COMMIT transactionName</code>

@advanced_1096_li
The transaction can now be committed or rolled back

@advanced_1097_li
If a problem occurs before the transaction was successfully committed or rolled back  (for example because a network problem occurred), the transaction is in the state 'in-doubt'

@advanced_1098_li
When re-connecting to the database, the in-doubt transactions can be listed  with <code>SELECT * FROM INFORMATION_SCHEMA.IN_DOUBT</code>

@advanced_1099_li
Each transaction in this list must now be committed or rolled back by executing <code>COMMIT TRANSACTION transactionName</code> or <code>ROLLBACK TRANSACTION transactionName</code>

@advanced_1100_li
The database needs to be closed and re-opened to apply the changes

@advanced_1101_h2
Compatibility

@advanced_1102_p
This database is (up to a certain point) compatible to other databases such as HSQLDB, MySQL and PostgreSQL. There are certain areas where H2 is incompatible.

@advanced_1103_h3
Transaction Commit when Autocommit is On

@advanced_1104_p
At this time, this database engine commits a transaction (if autocommit is switched on) just before returning the result. For a query, this means the transaction is committed even before the application scans through the result set, and before the result set is closed. Other database engines may commit the transaction in this case when the result set is closed.

@advanced_1105_h3
Keywords / Reserved Words

@advanced_1106_p
There is a list of keywords that can't be used as identifiers (table names, column names and so on), unless they are quoted (surrounded with double quotes). The list is currently:

@advanced_1107_p
CROSS, CURRENT_DATE, CURRENT_TIME, CURRENT_TIMESTAMP, DISTINCT, EXCEPT, EXISTS, FALSE, FOR, FROM, FULL, GROUP, HAVING, INNER, INTERSECT, IS, JOIN, LIKE, LIMIT, MINUS, NATURAL, NOT, NULL, ON, ORDER, PRIMARY, ROWNUM, SELECT, SYSDATE, SYSTIME, SYSTIMESTAMP, TODAY, TRUE, UNION, WHERE

@advanced_1108_p
Certain words of this list are keywords because they are functions that can be used without '()' for compatibility, for example CURRENT_TIMESTAMP.

@advanced_1109_h2
Standards Compliance

@advanced_1110_p
This database tries to be as much standard compliant as possible. For the SQL language, ANSI/ISO is the main standard. There are several versions that refer to the release date: SQL-92, SQL:1999, and SQL:2003. Unfortunately, the standard documentation is not freely available. Another problem is that important features are not standardized. Whenever this is the case, this database tries to be compatible to other databases.

@advanced_1111_h2
Run as Windows Service

@advanced_1112_p
Using a native wrapper / adapter, Java applications can be run as a Windows Service. There are various tools available to do that. The Java Service Wrapper from Tanuki Software, Inc. ( <a href="http://wrapper.tanukisoftware.org">http://wrapper.tanukisoftware.org</a> ) is included in the installation. Batch files are provided to install, start, stop and uninstall the H2 Database Engine Service. This service contains the TCP Server and the H2 Console web application. The batch files are located in the directory H2/service.

@advanced_1113_h3
Install the Service

@advanced_1114_p
The service needs to be registered as a Windows Service first. To do that, double click on 1_install_service.bat. If successful, a command prompt window will pop up and disappear immediately. If not, a message will appear.

@advanced_1115_h3
Start the Service

@advanced_1116_p
You can start the H2 Database Engine Service using the service manager of Windows, or by double clicking on 2_start_service.bat. Please note that the batch file does not print an error message if the service is not installed.

@advanced_1117_h3
Connect to the H2 Console

@advanced_1118_p
After installing and starting the service, you can connect to the H2 Console application using a browser. Double clicking on 3_start_browser.bat to do that. The default port (8082) is hard coded in the batch file.

@advanced_1119_h3
Stop the Service

@advanced_1120_p
To stop the service, double click on 4_stop_service.bat. Please note that the batch file does not print an error message if the service is not installed or started.

@advanced_1121_h3
Uninstall the Service

@advanced_1122_p
To uninstall the service, double click on 5_uninstall_service.bat. If successful, a command prompt window will pop up and disappear immediately. If not, a message will appear.

@advanced_1123_h2
ODBC Driver

@advanced_1124_p
This database does not come with its own ODBC driver at this time, but it supports the PostgreSQL network protocol. Therefore, the PostgreSQL ODBC driver can be used. Support for the PostgreSQL network protocol is quite new and should be viewed as experimental. It should not be used for production applications.

@advanced_1125_p
To use the PostgreSQL ODBC driver on 64 bit versions of Windows, first run <code>c:/windows/syswow64/odbcad32.exe</code> . At this point you set up your DSN just like you would on any other system. See also: <a href="http://archives.postgresql.org/pgsql-odbc/2005-09/msg00125.php">Re: ODBC Driver on Windows 64 bit</a>

@advanced_1126_h3
ODBC Installation

@advanced_1127_p
First, the ODBC driver must be installed. Any recent PostgreSQL ODBC driver should work, however version 8.2 (psqlodbc-08_02*) or newer is recommended. The Windows version of the PostgreSQL ODBC driver is available at <a href="http://www.postgresql.org/ftp/odbc/versions/msi">http://www.postgresql.org/ftp/odbc/versions/msi</a> .

@advanced_1128_h3
Starting the Server

@advanced_1129_p
After installing the ODBC driver, start the H2 Server using the command line:

@advanced_1130_p
The PG Server (PG for PostgreSQL protocol) is started as well. By default, databases are stored in the current working directory where the server is started. Use -baseDir to save databases in another directory, for example the user home directory:

@advanced_1131_p
The PG server can be started and stopped from within a Java application as follows:

@advanced_1132_p
By default, only connections from localhost are allowed. To allow remote connections, use <code>-pgAllowOthers</code> when starting the server.

@advanced_1133_h3
ODBC Configuration

@advanced_1134_p
After installing the driver, a new Data Source must be added. In Windows, run <code>odbcad32.exe</code> to open the Data Source Administrator. Then click on 'Add...' and select the PostgreSQL Unicode driver. Then click 'Finish'. You will be able to change the connection properties:

@advanced_1135_th
Property

@advanced_1136_th
Example

@advanced_1137_th
Remarks

@advanced_1138_td
Data Source

@advanced_1139_td
H2 Test

@advanced_1140_td
The name of the ODBC Data Source

@advanced_1141_td
Database

@advanced_1142_td
test

@advanced_1143_td
The database name. Only simple names are supported at this time;

@advanced_1144_td
relative or absolute path are not supported in the database name.

@advanced_1145_td
By default, the database is stored in the current working directory

@advanced_1146_td
where the Server is started except when the -baseDir setting is used.

@advanced_1147_td
The name must be at least 3 characters.

@advanced_1148_td
Server

@advanced_1149_td
localhost

@advanced_1150_td
The server name or IP address.

@advanced_1151_td
By default, only remote connections are allowed

@advanced_1152_td
User Name

@advanced_1153_td
sa

@advanced_1154_td
The database user name.

@advanced_1155_td
SSL Mode

@advanced_1156_td
disabled

@advanced_1157_td
At this time, SSL is not supported.

@advanced_1158_td
Port

@advanced_1159_td
5435

@advanced_1160_td
The port where the PG Server is listening.

@advanced_1161_td
Password

@advanced_1162_td
sa

@advanced_1163_td
The database password.

@advanced_1164_p
To improve performance, please enable 'server side prepare' under Options / Datasource / Page 2 / Server side prepare.

@advanced_1165_p
Afterwards, you may use this data source.

@advanced_1166_h3
PG Protocol Support Limitations

@advanced_1167_p
At this time, only a subset of the PostgreSQL network protocol is implemented. Also, there may be compatibility problems on the SQL level, with the catalog, or with text encoding. Problems are fixed as they are found. Currently, statements can not be canceled when using the PG protocol.

@advanced_1168_p
PostgreSQL ODBC Driver Setup requires a database password; that means it is not possible to connect to H2 databases without password. This is a limitation of the ODBC driver.

@advanced_1169_h3
Security Considerations

@advanced_1170_p
Currently, the PG Server does not support challenge response or encrypt passwords. This may be a problem if an attacker can listen to the data transferred between the ODBC driver and the server, because the password is readable to the attacker. Also, it is currently not possible to use encrypted SSL connections. Therefore the ODBC driver should not be used where security is important.

@advanced_1171_h2
Using H2 in Microsoft .NET

@advanced_1172_p
The database can be used from Microsoft .NET even without using Java, by using IKVM.NET. You can access a H2 database on .NET using the JDBC API, or using the ADO.NET interface.

@advanced_1173_h3
Using the ADO.NET API on .NET

@advanced_1174_p
An implementation of the ADO.NET interface is available in the open source project <a href="http://code.google.com/p/h2sharp">H2Sharp</a> .

@advanced_1175_h3
Using the JDBC API on .NET

@advanced_1176_li
Install the .NET Framework from <a href="http://www.microsoft.com">Microsoft</a> .  Mono has not yet been tested.

@advanced_1177_li
Install <a href="http://www.ikvm.net">IKVM.NET</a> .

@advanced_1178_li
Copy the h2*.jar file to ikvm/bin

@advanced_1179_li
Run the H2 Console using: <code>ikvm -jar h2*.jar</code>

@advanced_1180_li
Convert the H2 Console to an .exe file using: <code>ikvmc -target:winexe h2*.jar</code> .  You may ignore the warnings.

@advanced_1181_li
Create a .dll file using (change the version accordingly): <code>ikvmc.exe -target:library -version:1.0.69.0 h2*.jar</code>

@advanced_1182_p
If you want your C# application use H2, you need to add the h2.dll and the IKVM.OpenJDK.ClassLibrary.dll to your C# solution. Here some sample code:

@advanced_1183_h2
ACID

@advanced_1184_p
In the database world, ACID stands for:

@advanced_1185_li
Atomicity: Transactions must be atomic, meaning either all tasks are performed or none.

@advanced_1186_li
Consistency: All operations must comply with the defined constraints.

@advanced_1187_li
Isolation: Transactions must be isolated from each other.

@advanced_1188_li
Durability: Committed transaction will not be lost.

@advanced_1189_h3
Atomicity

@advanced_1190_p
Transactions in this database are always atomic.

@advanced_1191_h3
Consistency

@advanced_1192_p
By default, this database is always in a consistent state. Referential integrity rules are enforced except when explicitly disabled.

@advanced_1193_h3
Isolation

@advanced_1194_p
For H2, as with most other database systems, the default isolation level is 'read committed'. This provides better performance, but also means that transactions are not completely isolated. H2 supports the transaction isolation levels 'serializable', 'read committed', and 'read uncommitted'.

@advanced_1195_h3
Durability

@advanced_1196_p
This database does not guarantee that all committed transactions survive a power failure. Tests show that all databases sometimes lose transactions on power failure (for details, see below). Where losing transactions is not acceptable, a laptop or UPS (uninterruptible power supply) should be used. If durability is required for all possible cases of hardware failure, clustering should be used, such as the H2 clustering mode.

@advanced_1197_h2
Durability Problems

@advanced_1198_p
Complete durability means all committed transaction survive a power failure. Some databases claim they can guarantee durability, but such claims are wrong. A durability test was run against H2, HSQLDB, PostgreSQL, and Derby. All of those databases sometimes lose committed transactions. The test is included in the H2 download, see org.h2.test.poweroff.Test.

@advanced_1199_h3
Ways to (Not) Achieve Durability

@advanced_1200_p
Making sure that committed transactions are not lost is more complicated than it seems first. To guarantee complete durability, a database must ensure that the log record is on the hard drive before the commit call returns. To do that, databases use different methods. One is to use the 'synchronous write' file access mode. In Java, RandomAccessFile supports the modes "rws" and "rwd":

@advanced_1201_li
rwd: Every update to the file's content is written synchronously to the underlying storage device.

@advanced_1202_li
rws: In addition to rwd, every update to the metadata is written synchronously.

@advanced_1203_p
A test (org.h2.test.poweroff.TestWrite) with one of those modes achieves around 50 thousand write operations per second. Even when the operating system write buffer is disabled, the write rate is around 50 thousand operations per second. This feature does not force changes to disk because it does not flush all buffers. The test updates the same byte in the file again and again. If the hard drive was able to write at this rate, then the disk would need to make at least 50 thousand revolutions per second, or 3 million RPM (revolutions per minute). There are no such hard drives. The hard drive used for the test is about 7200 RPM, or about 120 revolutions per second. There is an overhead, so the maximum write rate must be lower than that.

@advanced_1204_p
Calling fsync flushes the buffers. There are two ways to do that in Java:

@advanced_1205_li
FileDescriptor.sync(). The documentation says that this forces all system buffers to synchronize with the underlying device. Sync is supposed to return after all in-memory modified copies of buffers associated with this FileDescriptor have been written to the physical medium.

@advanced_1206_li
FileChannel.force() (since JDK 1.4). This method is supposed to force any updates to this channel's file to be written to the storage device that contains it.

@advanced_1207_p
By default, MySQL calls fsync for each commit. When using one of those methods, only around 60 write operations per second can be achieved, which is consistent with the RPM rate of the hard drive used. Unfortunately, even when calling FileDescriptor.sync() or FileChannel.force(), data is not always persisted to the hard drive, because most hard drives do not obey fsync(): see <a href="http://hardware.slashdot.org/article.pl?sid=05/05/13/0529252">Your Hard Drive Lies to You</a> . In Mac OS X, fsync does not flush hard drive buffers. See <a href="http://lists.apple.com/archives/darwin-dev/2005/Feb/msg00072.html">Bad fsync?</a> . So the situation is confusing, and tests prove there is a problem.

@advanced_1208_p
Trying to flush hard drive buffers is hard, and if you do the performance is very bad. First you need to make sure that the hard drive actually flushes all buffers. Tests show that this can not be done in a reliable way. Then the maximum number of transactions is around 60 per second. Because of those reasons, the default behavior of H2 is to delay writing committed transactions.

@advanced_1209_p
In H2, after a power failure, a bit more than one second of committed transactions may be lost. To change the behavior, use SET WRITE_DELAY and CHECKPOINT SYNC. Most other databases support commit delay as well. In the performance comparison, commit delay was used for all databases that support it.

@advanced_1210_h3
Running the Durability Test

@advanced_1211_p
To test the durability / non-durability of this and other databases, you can use the test application in the package org.h2.test.poweroff. Two computers with network connection are required to run this test. One computer just listens, while the test application is run (and power is cut) on the other computer. The computer with the listener application opens a TCP/IP port and listens for an incoming connection. The second computer first connects to the listener, and then created the databases and starts inserting records. The connection is set to 'autocommit', which means after each inserted record a commit is performed automatically. Afterwards, the test computer notifies the listener that this record was inserted successfully. The listener computer displays the last inserted record number every 10 seconds. Now, switch off the power manually, then restart the computer, and run the application again. You will find out that in most cases, none of the databases contains all the records that the listener computer knows about. For details, please consult the source code of the listener and test application.

@advanced_1212_h2
Using the Recover Tool

@advanced_1213_p
The recover tool can be used to extract the contents of a data file, even if the database is corrupted. It also extracts the content of the log file or large objects (CLOB or BLOB). To run the tool, type on the command line:

@advanced_1214_p
For each database in the current directory, a text file will be created. This file contains raw insert statements (for the data) and data definition (DDL) statements to recreate the schema of the database. This file can be executed using the RunScript tool or a <code>RUNSCRIPT FROM</code> SQL statement. The script includes at least one CREATE USER statement. If you run the script against a database that was created with the same user, or if there are conflicting users, running the script will fail. Consider running the script against a database that was created with a user name that is not in the script.

@advanced_1215_h2
File Locking Protocols

@advanced_1216_p
Whenever a database is opened, a lock file is created to signal other processes that the database is in use. If the database is closed, or if the process that opened the database terminates, this lock file is deleted.

@advanced_1217_p
In special cases (if the process did not terminate normally, for example because there was a power failure), the lock file is not deleted by the process that created it. That means the existence of the lock file is not a safe protocol for file locking. However, this software uses a challenge-response protocol to protect the database files. There are two methods (algorithms) implemented to provide both security (that is, the same database files cannot be opened by two processes at the same time) and simplicity (that is, the lock file does not need to be deleted manually by the user). The two methods are 'file method' and 'socket methods'.

@advanced_1218_h3
File Locking Method 'File'

@advanced_1219_p
The default method for database file locking is the 'File Method'. The algorithm is:

@advanced_1220_li
When the lock file does not exist, it is created (using the atomic operation File.createNewFile). Then, the process waits a little bit (20ms) and checks the file again. If the file was changed during this time, the operation is aborted. This protects against a race condition when a process deletes the lock file just after one create it, and a third process creates the file again. It does not occur if there are only two writers.

@advanced_1221_li
If the file can be created, a random number is inserted together with the locking method ('file'). Afterwards, a watchdog thread is started that checks regularly (every second once by default) if the file was deleted or modified by another (challenger) thread / process. Whenever that occurs, the file is overwritten with the old data. The watchdog thread runs with high priority so that a change to the lock file does not get through undetected even if the system is very busy. However, the watchdog thread does use very little resources (CPU time), because it waits most of the time. Also, the watchdog only reads from the hard disk and does not write to it.

@advanced_1222_li
If the lock file exists, and it was modified in the 20 ms, the process waits for some time (up to 10 times). If it was still changed, an exception is thrown (database is locked). This is done to eliminate race conditions with many concurrent writers. Afterwards, the file is overwritten with a new version (challenge). After that, the thread waits for 2 seconds. If there is a watchdog thread protecting the file, he will overwrite the change and this process will fail to lock the database. However, if there is no watchdog thread, the lock file will still be as written by this thread. In this case, the file is deleted and atomically created again. The watchdog thread is started in this case and the file is locked.

@advanced_1223_p
This algorithm is tested with over 100 concurrent threads. In some cases, when there are many concurrent threads trying to lock the database, they block each other (meaning the file cannot be locked by any of them) for some time. However, the file never gets locked by two threads at the same time. However using that many concurrent threads / processes is not the common use case. Generally, an application should throw an error to the user if it cannot open a database, and not try again in a (fast) loop.

@advanced_1224_h3
File Locking Method 'Socket'

@advanced_1225_p
There is a second locking mechanism implemented, but disabled by default. To use it, append <code>;FILE_LOCK=SOCKET</code> to the database URL. The algorithm is:

@advanced_1226_li
If the lock file does not exist, it is created. Then a server socket is opened on a defined port, and kept open. The port and IP address of the process that opened the database is written into the lock file.

@advanced_1227_li
If the lock file exists, and the lock method is 'file', then the software switches to the 'file' method.

@advanced_1228_li
If the lock file exists, and the lock method is 'socket', then the process checks if the port is in use. If the original process is still running, the port is in use and this process throws an exception (database is in use). If the original process died (for example due to a power failure, or abnormal termination of the virtual machine), then the port was released. The new process deletes the lock file and starts again.

@advanced_1229_p
This method does not require a watchdog thread actively polling (reading) the same file every second. The problem with this method is, if the file is stored on a network share, two processes (running on different computers) could still open the same database files, if they do not have a direct TCP/IP connection.

@advanced_1230_h2
Protection against SQL Injection

@advanced_1231_h3
What is SQL Injection

@advanced_1232_p
This database engine provides a solution for the security vulnerability known as 'SQL Injection'. Here is a short description of what SQL injection means. Some applications build SQL statements with embedded user input such as:

@advanced_1233_p
If this mechanism is used anywhere in the application, and user input is not correctly filtered or encoded, it is possible for a user to inject SQL functionality or statements by using specially built input such as (in this example) this password: ' OR ''='. In this case the statement becomes:

@advanced_1234_p
Which is always true no matter what the password stored in the database is. For more information about SQL Injection, see Glossary and Links.

@advanced_1235_h3
Disabling Literals

@advanced_1236_p
SQL Injection is not possible if user input is not directly embedded in SQL statements. A simple solution for the problem above is to use a PreparedStatement:

@advanced_1237_p
This database provides a way to enforce usage of parameters when passing user input to the database. This is done by disabling embedded literals in SQL statements. To do this, execute the statement:

@advanced_1238_p
Afterwards, SQL statements with text and number literals are not allowed any more. That means, SQL statement of the form WHERE NAME='abc' or WHERE CustomerId=10 will fail. It is still possible to use PreparedStatements and parameters as described above. Also, it is still possible to generate SQL statements dynamically, and use the Statement API, as long as the SQL statements do not include literals. There is also a second mode where number literals are allowed: SET ALLOW_LITERALS NUMBERS. To allow all literals, execute SET ALLOW_LITERALS ALL (this is the default setting). Literals can only be enabled or disabled by an administrator.

@advanced_1239_h3
Using Constants

@advanced_1240_p
Disabling literals also means disabling hard-coded 'constant' literals. This database supports defining constants using the CREATE CONSTANT command. Constants can be defined only when literals are enabled, but used even when literals are disabled. To avoid name clashes with column names, constants can be defined in other schemas:

@advanced_1241_p
Even when literals are enabled, it is better to use constants instead of hard-coded number or text literals in queries or views. With constants, typos are found at compile time, the source code is easier to understand and change.

@advanced_1242_h3
Using the ZERO() Function

@advanced_1243_p
It is not required to create a constant for the number 0 as there is already a built-in function ZERO():

@advanced_1244_h2
Restricting Class Loading and Usage

@advanced_1245_p
By default there is no restriction on loading classes and executing Java code for admins. That means an admin may call system functions such as System.setProperty by executing:

@advanced_1246_p
To restrict users (including admins) from loading classes and executing code, the list of allowed classes can be set in the system property h2.allowedClasses in the form of a comma separated list of classes or patterns (items ending with '*'). By default all classes are allowed. Example:

@advanced_1247_p
This mechanism is used for all user classes, including database event listeners, trigger classes, user-defined functions, user-defined aggregate functions, and JDBC driver classes (with the exception of the H2 driver) when using the H2 Console.

@advanced_1248_h2
Security Protocols

@advanced_1249_p
The following paragraphs document the security protocols used in this database. These descriptions are very technical and only intended for security experts that already know the underlying security primitives.

@advanced_1250_h3
User Password Encryption

@advanced_1251_p
When a user tries to connect to a database, the combination of user name, @, and password are hashed using SHA-256, and this hash value is transmitted to the database. This step does not protect against an attacker that re-uses the value if he is able to listen to the (unencrypted) transmission between the client and the server. But, the passwords are never transmitted as plain text, even when using an unencrypted connection between client and server. That means if a user reuses the same password for different things, this password is still protected up to some point. See also 'RFC 2617 - HTTP Authentication: Basic and Digest Access Authentication' for more information.

@advanced_1252_p
When a new database or user is created, a new cryptographically secure random salt value is generated. The size of the salt is 64 bits. Using the random salt reduces the risk of an attacker pre-calculating hash values for many different (commonly used) passwords.

@advanced_1253_p
The combination of user-password hash value (see above) and salt is hashed using SHA-256. The resulting value is stored in the database. When a user tries to connect to the database, the database combines user-password hash value with the stored salt value and calculates the hash value. Other products use multiple iterations (hash the hash value again and again), but this is not done in this product to reduce the risk of denial of service attacks (where the attacker tries to connect with bogus passwords, and the server spends a lot of time calculating the hash value for each password). The reasoning is: if the attacker has access to the hashed passwords, he also has access to the data in plain text, and therefore does not need the password any more. If the data is protected by storing it on another computer and only accessible remotely, then the iteration count is not required at all.

@advanced_1254_h3
File Encryption

@advanced_1255_p
The database files can be encrypted using two different algorithms: AES-128 and XTEA (using 32 rounds). The reasons for supporting XTEA is performance (XTEA is about twice as fast as AES) and to have an alternative algorithm if AES is suddenly broken.

@advanced_1256_p
When a user tries to connect to an encrypted database, the combination of the word 'file', @, and the file password is hashed using SHA-256. This hash value is transmitted to the server.

@advanced_1257_p
When a new database file is created, a new cryptographically secure random salt value is generated. The size of the salt is 64 bits. The combination of the file password hash and the salt value is hashed 1024 times using SHA-256. The reason for the iteration is to make it harder for an attacker to calculate hash values for common passwords.

@advanced_1258_p
The resulting hash value is used as the key for the block cipher algorithm (AES-128 or XTEA with 32 rounds). Then, an initialization vector (IV) key is calculated by hashing the key again using SHA-256. This is to make sure the IV is unknown to the attacker. The reason for using a secret IV is to protect against watermark attacks.

@advanced_1259_p
Before saving a block of data (each block is 8 bytes long), the following operations are executed: First, the IV is calculated by encrypting the block number with the IV key (using the same block cipher algorithm). This IV is combined with the plain text using XOR. The resulting data is encrypted using the AES-128 or XTEA algorithm.

@advanced_1260_p
When decrypting, the operation is done in reverse. First, the block is decrypted using the key, and then the IV is calculated combined with the decrypted text using XOR.

@advanced_1261_p
Therefore, the block cipher mode of operation is CBC (cipher-block chaining), but each chain is only one block long. The advantage over the ECB (electronic codebook) mode is that patterns in the data are not revealed, and the advantage over multi block CBC is that flipped cipher text bits are not propagated to flipped plaintext bits in the next block.

@advanced_1262_p
Database encryption is meant for securing the database while it is not in use (stolen laptop and so on). It is not meant for cases where the attacker has access to files while the database is in use. When he has write access, he can for example replace pieces of files with pieces of older versions and manipulate data like this.

@advanced_1263_p
File encryption slows down the performance of the database engine. Compared to unencrypted mode, database operations take about 2.2 times longer when using XTEA, and 2.5 times longer using AES (embedded mode).

@advanced_1264_h3
Wrong Password / User Name Delay

@advanced_1265_p
To protect against remote brute force password attacks, the delay after each unsuccessful login gets double as long. Use the system properties h2.delayWrongPasswordMin and h2.delayWrongPasswordMax to change the minimum (the default is 250 milliseconds) or maximum delay (the default is 4000 milliseconds, or 4 seconds). The delay only applies for those using the wrong password. Normally there is no delay for a user that knows the correct password, with one exception: after using the wrong password, there is a delay of up to (randomly distributed) the same delay as for a wrong password. This is to protect against parallel brute force attacks, so that an attacker needs to wait for the whole delay. Delays are synchronized. This is also required to protect against parallel attacks.

@advanced_1266_p
There is only one exception message for both wrong user and for wrong password, to make it harder to get the list of user names. It is not possible from the stack trace to see if the user name was wrong or the password.

@advanced_1267_h3
HTTPS Connections

@advanced_1268_p
The web server supports HTTP and HTTPS connections using SSLServerSocket. There is a default self-certified certificate to support an easy starting point, but custom certificates are supported as well.

@advanced_1269_h2
SSL/TLS Connections

@advanced_1270_p
Remote SSL/TLS connections are supported using the Java Secure Socket Extension (SSLServerSocket / SSLSocket). By default, anonymous SSL is enabled. The default cipher suite is <code>SSL_DH_anon_WITH_RC4_128_MD5</code> .

@advanced_1271_p
To use your own keystore, set the system properties <code>javax.net.ssl.keyStore</code> and <code>javax.net.ssl.keyStorePassword</code> before starting the H2 server and client. See also <a href="http://java.sun.com/javase/6/docs/technotes/guides/security/jsse/JSSERefGuide.html#CustomizingStores">Customizing the Default Key and Trust Stores, Store Types, and Store Passwords</a> for more information.

@advanced_1272_p
To disable anonymous SSL, set the system property <code>h2.enableAnonymousSSL</code> to false.

@advanced_1273_h2
Universally Unique Identifiers (UUID)

@advanced_1274_p
This database supports the UUIDs. Also supported is a function to create new UUIDs using a cryptographically strong pseudo random number generator. With random UUIDs, the chance of two having the same value can be calculated using the probability theory. See also 'Birthday Paradox'. Standardized randomly generated UUIDs have 122 random bits. 4 bits are used for the version (Randomly generated UUID), and 2 bits for the variant (Leach-Salz). This database supports generating such UUIDs using the built-in function RANDOM_UUID(). Here is a small program to estimate the probability of having two identical UUIDs after generating a number of values:

@advanced_1275_p
Some values are:

@advanced_1276_p
To help non-mathematicians understand what those numbers mean, here a comparison: One's annual risk of being hit by a meteorite is estimated to be one chance in 17 billion, that means the probability is about 0.000'000'000'06.

@advanced_1277_h2
Settings Read from System Properties

@advanced_1278_p
Some settings of the database can be set on the command line using -DpropertyName=value. It is usually not required to change those settings manually. The settings are case sensitive. Example:

@advanced_1279_p
The current value of the settings can be read in the table INFORMATION_SCHEMA.SETTINGS.

@advanced_1280_p
For a complete list of settings, see <a href="../javadoc/org/h2/constant/SysProperties.html">SysProperties</a> .

@advanced_1281_h2
Setting the Server Bind Address

@advanced_1282_p
Usually server sockets accept connections on any/all local addresses. This may be a problem on multi-homed hosts. To bind only to one address, use the system property h2.bindAddress. This setting is used for both regular server sockets and for SSL server sockets. IPv4 and IPv6 address formats are supported.

@advanced_1283_h2
Limitations

@advanced_1284_p
This database has the following known limitations:

@advanced_1285_li
The maximum file size is currently 256 GB for the data, and 256 GB for the index. This number is excluding BLOB and CLOB data: Every CLOB or BLOB can be up to 256 GB as well.

@advanced_1286_li
The maximum file size for FAT or FAT32 file systems is 4 GB. That means when using FAT or FAT32, the limit is 4 GB for the data. This is the limitation of the file system. The database does provide a workaround for this problem, it is to use the file name prefix 'split:'. In that case files are split into files of 1 GB by default. An example database URL is: <code>jdbc:h2:split:~/test</code> .

@advanced_1287_li
There is a limit on the complexity of SQL statements. Statements of the following form will result in a stack overflow exception:

@advanced_1288_li
There is no limit for the following entities, except the memory and storage capacity:  maximum identifier length, maximum number of tables, maximum number of columns,  maximum number of indexes, maximum number of parameters,  maximum number of triggers, and maximum number of other database objects.

@advanced_1289_li
For limitations on data types, see the documentation of the respective Java data type  or the data type documentation of this database.

@advanced_1290_h2
Glossary and Links

@advanced_1291_th
Term

@advanced_1292_th
Description

@advanced_1293_td
AES-128

@advanced_1294_td
A block encryption algorithm. See also: <a
            href="http://en.wikipedia.org/wiki/Advanced_Encryption_Standard">Wikipedia:   AES</a>

@advanced_1295_td
Birthday Paradox

@advanced_1296_td
Describes the higher than expected probability that two   persons in a room have the same birthday. Also valid for randomly   generated UUIDs. See also: <a
            href="http://en.wikipedia.org/wiki/Birthday_paradox">Wikipedia:   Birthday Paradox</a>

@advanced_1297_td
Digest

@advanced_1298_td
Protocol to protect a password (but not to protect data).   See also: <a href="http://www.faqs.org/rfcs/rfc2617.html">RFC   2617: HTTP Digest Access Authentication</a>

@advanced_1299_td
GCJ

@advanced_1300_td
Compiler for Java. <a href="http://gcc.gnu.org/java">GNU   Compiler for the Java</a> and <a
            href="http://www.dobysoft.com/products/nativej">NativeJ   (commercial)</a>

@advanced_1301_td
HTTPS

@advanced_1302_td
A protocol to provide security to HTTP connections. See   also: <a href="http://www.ietf.org/rfc/rfc2818.txt">RFC 2818:   HTTP Over TLS</a>

@advanced_1303_td
Modes of Operation

@advanced_1304_a
Wikipedia:   Block cipher modes of operation

@advanced_1305_td
Salt

@advanced_1306_td
Random number to increase the security of passwords. See   also: <a href="http://en.wikipedia.org/wiki/Key_derivation_function">Wikipedia:   Key derivation function</a>

@advanced_1307_td
SHA-256

@advanced_1308_td
A cryptographic one-way hash function. See also: <a
            href="http://en.wikipedia.org/wiki/SHA_family">Wikipedia: SHA   hash functions</a>

@advanced_1309_td
SQL Injection

@advanced_1310_td
A security vulnerability where an application embeds SQL   statements or expressions in user input. See also: <a
            href="http://en.wikipedia.org/wiki/SQL_injection">Wikipedia:   SQL Injection</a>

@advanced_1311_td
Watermark Attack

@advanced_1312_td
Security problem of certain encryption programs where the   existence of certain data can be proven without decrypting. For more   information, search in the internet for 'watermark attack   cryptoloop'

@advanced_1313_td
SSL/TLS

@advanced_1314_td
Secure Sockets Layer / Transport Layer Security. See also: <a href="http://java.sun.com/products/jsse/">Java Secure Socket   Extension (JSSE)</a>

@advanced_1315_td
XTEA

@advanced_1316_td
A block encryption algorithm. See also: <a
            href="http://en.wikipedia.org/wiki/XTEA">Wikipedia: XTEA</a>

@build_1000_h1
Build

@build_1001_a
Portability

@build_1002_a
Environment

@build_1003_a
Building the Software

@build_1004_a
Build Targets

@build_1005_a
Using Maven 2

@build_1006_a
Translating

@build_1007_a
Providing Patches

@build_1008_a
Automated Build

@build_1009_h2
Portability

@build_1010_p
This database is written in Java and therefore works on many platforms. It can also be compiled to a native executable using GCJ.

@build_1011_h2
Environment

@build_1012_p
A Java Runtime Environment (JRE) version 1.4 or higher is required to run this database.

@build_1013_p
To build the database executables, the following software stack was used. Newer version or compatible software works too.

@build_1014_li
Mac OS X and Windows XP

@build_1015_a
Sun JDK Version 1.4, 1.5, and 1.6

@build_1016_a
Eclipse Version 3.4

@build_1017_li
Eclipse Plugins: <a href="http://subclipse.tigris.org">Subclipse 1.4.6</a> , <a href="http://eclipse-cs.sourceforge.net">Eclipse Checkstyle Plug-in 4.4.2</a> , <a href="http://www.eclemma.org">EclEmma Java Code Coverage 1.3.0</a>

@build_1018_a
Emma Java Code Coverage

@build_1019_a
Mozilla Firefox 3.0

@build_1020_a
OpenOffice 3.0

@build_1021_a
NSIS 2.38

@build_1022_li
(Nullsoft Scriptable Install System)

@build_1023_a
Maven 2.0.9

@build_1024_h2
Building the Software

@build_1025_p
You need to install a JDK, for example the Sun JDK version 1.4, 1.5 or 1.6. On the command line, go to the directory h2 and execute the following command:

@build_1026_p
For Linux and OS X, use <code>./build.sh</code> instead of <code>build</code> .

@build_1027_p
You will get a list of targets. If you want to build the jar file, execute (Windows):

@build_1028_h3
Switching the Source Code

@build_1029_p
By default the source code uses Java 1.5 features, however Java 1.4 and 1.5 are supported as well. To switch the source code to the install version of Java, run:

@build_1030_h2
Build Targets

@build_1031_p
The build system can generate smaller jar files as well. The following targets are currently supported:

@build_1032_li
jarClient: Create the h2client.jar. This only contains the JDBC client.

@build_1033_li
jarSmall: Create the file h2small.jar. This only contains the embedded database. Debug information is disabled.

@build_1034_li
jarJaqu: Create the file h2jaqu.jar. This only contains the JaQu (Java Query) implementation. All other jar files do not include JaQu.

@build_1035_li
javadocImpl: Create the Javadocs of the implementation.

@build_1036_p
To create the h2client.jar file, go to the directory h2 and execute the following command:

@build_1037_h2
Using Maven 2

@build_1038_h3
Using a Central Repository

@build_1039_p
You can include the database in your Maven 2 project as a dependency. Example:

@build_1040_p
New versions of this database are first uploaded to http://hsql.sourceforge.net/m2-repo/ and then automatically synchronized with the main maven repository; however after a new release it may take a few hours before they are available there.

@build_1041_h3
Using Snapshot Version

@build_1042_p
To build a 'snapshot' H2 .jar file and upload it the to the local Maven 2 repository, execute the following command:

@build_1043_p
Afterwards, you can include the database in your Maven 2 project as a dependency:

@build_1044_h2
Translating

@build_1045_p
The translation of this software is split into the following parts:

@build_1046_li
H2 Console: src/main/org/h2/server/web/res/_text_*.properties

@build_1047_li
Error messages: src/main/org/h2/res/_messages_*.properties

@build_1048_li
Web site: src/docsrc/text/_docs_*.utf8.txt

@build_1049_p
To translate the H2 Console, start it and select Preferences / Translate. The conversion between UTF-8 and Java encoding (using the \u syntax), as well as the HTML entities (&amp;#..;) is automated by running the tool PropertiesToUTF8. The web site translation is automated as well, using <code>build docs</code> .

@build_1050_h2
Providing Patches

@build_1051_p
If you like to provide patches, please consider the following guidelines to simplify merging them:

@build_1052_li
Only use Java 1.4 features (do not use Java 1.5 or 1.6) (see Environment).

@build_1053_li
Follow the coding style used in the project, and use Checkstyle (see above) to verify.  For example, do not use tabs (use spaces instead).  The checkstyle configuration is in <code>src/installer/checkstyle.xml</code> .

@build_1054_li
Please provide test cases and integrate them into the test suite.  For Java level tests, see <code>src/test/org/h2/test/TestAll.java</code> .  For SQL level tests, see <code>src/test/org/h2/test/test.in.txt</code> or <code>testSimple.in.txt</code> .

@build_1055_li
The test cases should cover at least 90% of the changed and new code; use a code coverage tool to verify that (see above).  or use the build target 'coverage'.

@build_1056_li
Verify that you did not break other features: Run the test cases by executing <code>build test</code> .

@build_1057_li
Provide end user documentation if required ( <code>src/docsrc/html/*</code> ).

@build_1058_li
Document grammar changes in <code>src/main/org/h2/res/help.csv</code>

@build_1059_li
Provide a change log entry ( <code>src/docsrc/html/changelog.html</code> ).

@build_1060_li
Verify the spelling using <code>build spellcheck</code> . If required  add the new words to <code>src/tools/org/h2/build/doc/dictionary.txt</code> .

@build_1061_li
Verify the formatting using <code>build docs</code> and <code>build javadoc</code> .

@build_1062_li
Submit patches as .patch files (compressed if big). To create a patch using Eclipse, use Team / Create Patch.

@build_1063_h2
Automated Build

@build_1064_p
This build process is automated and runs regularly. The build process includes running the tests and code coverage, using the command line <code>./build.sh clean jar coverage -Dh2.ftpPassword=... uploadBuild</code> . The last results are available here:

@build_1065_a
Test Output

@build_1066_a
Code Coverage Summary

@build_1067_a
Code Coverage Details (download, 1.3 MB)

@build_1068_a
Build Newsfeed

@build_1069_a
Latest Jar File (download, 1 MB)

@changelog_1000_h1
Change Log

@changelog_1001_h2
Next Version (unreleased)

@changelog_1002_li
-

@changelog_1003_h2
Version 1.1.113 (2009-05-21)

@changelog_1004_li
Shell tool: the built-in commands EXIT, HELP, ?, LIST, and so on didn't  work with a semicolon at the end.

@changelog_1005_li
JDK 1.5 is now required to build the jar file. However it is still possible to create  a jar file for Java 1.4. For details, see buildRelease.sh and buildRelease.bat.  As an alternative, compile using JDK 1.5 or 1.6 and use Retrotranslator to create a Java 1.4  version (http://retrotranslator.sourceforge.net/).

@changelog_1006_li
When deleting or updating many rows in a table, the space in the index  file was not re-used in the default mode (persistent database, b-tree index,  LOG=1). This caused the index file to grow over time. Workarounds were to  delete and re-created the index file, alter the table (add a remove a column),  or append ;LOG=2 to the database URL. To disable the change, set the system  property h2.reuseSpaceBtreeIndex to false.

@changelog_1007_li
Identifiers with a digit and then a dollar sign didn't work. Example: A1$B.

@changelog_1008_li
MS SQL Server compatibility: support for linked tables with  NVARCHAR, NCHAR, NCLOB, and LONGNVARCHAR.

@changelog_1009_li
Android: Workaround for a problem when using read-only databases in zip files  (skip seems to be implemented incorrectly on the Android system).

@changelog_1010_li
Calling execute() or prepareStatement() with null as the SQL statement  now throws an exception.

@changelog_1011_li
Benchmark: the number of executed statements was incorrect. The H2 database  was loaded at the beginning of the test to collect results, now it is loaded at the very end.  Thanks to Fred Toussi from HSQLDB for reporting those problems. However the changed  do not affect the relative performance.

@changelog_1012_li
H2 Console: command line settings are no longer stored in the properties file.  They are now only used for the current process, except if they are explicitly saved.

@changelog_1013_li
Cache: support for a second level soft-references cache.  To enable it, append ;CACHE_TYPE=SOFT_LRU (or SOFT_TQ) to the database URL, or  set the system property h2.cacheTypeDefault to "SOFT_LRU" / "SOFT_TQ".  Enabling the second level cache reduces performance for  small databases, but speeds up large databases. It makes sense to use it  if the available memory size is unknown. Thanks a lot to Jan Kotek!

@changelog_1014_h2
Version 1.1.112 (2009-05-01)

@changelog_1015_li
JdbcPreparedStatement.toString() could throw a NullPointerException.

@changelog_1016_li
EclipseLink: Added H2Platform.supportsIdentity().

@changelog_1017_li
Connection pool: the default login timeout is now 5 minutes.

@changelog_1018_li
After truncating tables, opening large databases could become slow  because indexes were always re-built unnecessarily when opening.

@changelog_1019_li
More bugs in the server-less multi-connection mode have been fixed:  Sometimes parameters of prepared statements were lost when a reconnecting.  Concurrent read operations were slow.  To improve performance, executeQuery(..) must be used for queries  (execute(..) switches to the write mode, which is slow).

@changelog_1020_li
GROUP BY queries with a self-join (join to the same table) that were grouped by  columns with indexes returned the wrong result in some cases.

@changelog_1021_li
Improved error message when the .lock.db file modification time is in the future.

@changelog_1022_li
The MERGE statement now returns 0 as the generated key if the row was updated.

@changelog_1023_li
Running code coverage is now automated.

@changelog_1024_li
A file system implementation can now be registered using FileSystem.register.

@changelog_1025_li
The database file system is no longer included in the jar file, it moved to the test section.

@changelog_1026_h2
Version 1.1.111 (2009-04-10)

@changelog_1027_li
In-memory databases can now run inside the Google App Engine.

@changelog_1028_li
Queries that are ordered by an indexed column returned no rows in certain cases  (if all rows were deleted from the table previously, and there is a low number of rows  in the table, and when not using other conditions, and when using the default b tree index).

@changelog_1029_li
The wrong exception was thrown when using unquoted text for  the SQL statements COMMENT, ALTER USER, and SET PASSWORD.

@changelog_1030_li
The built-in connection pool did not roll back transactions and  enable autocommit enabled after closing a connection.

@changelog_1031_li
Sometimes a StackOverflow occurred when checking for deadlock. See also  http://code.google.com/p/h2database/issues/detail?id=61

@changelog_1032_li
The Shell tool no longer truncates results with only one column, and displays  a message if data was truncated.

@changelog_1033_h2
Version 1.1.110 (2009-04-03)

@changelog_1034_li
Support for not persistent in-memory tables in regular (persistent) databases  using CREATE MEMORY TABLE(..) NOT PERSISTENT. Thanks a lot to Sergi Vladykin for the patch!

@changelog_1035_li
The H2 Console trimmed the password (removed leading and trailing spaces).  This is no longer the case, to support encrypted H2 database with an empty user password.

@changelog_1036_li
The data type of a SUBSTRING method was wrong.

@changelog_1037_li
ResultSet.findColumn and get methods with column label parameters  now also check for matching column names (like most databases except MySQL).

@changelog_1038_li
H2 Console: the browser system property now supports a list of arguments.  Example: java -Dh2.browser="open,-a,Safari,%url" ...

@changelog_1039_li
Improved Javadoc navigation (similar to Scaladoc).

@changelog_1040_li
H2 Console: auto-complete of identifiers did not work correctly  for H2 databases in MySQL mode.

@changelog_1041_li
DISTINCT and GROUP BY on a CLOB column was broken.

@changelog_1042_li
The FTP server moved to the tools section and is no longer included in the h2*.jar file.

@changelog_1043_li
Improved error message for unsupported features:  now the message says what exactly is not supported.

@changelog_1044_li
Improved OSGi support.

@changelog_1045_li
Some internal caches did not use the LRU mechanism. Fixed  (LOB file list, optimizer cost cache, trace system, view indexes, collection keys,  compressed in-memory file system).

@changelog_1046_li
The API of the tools changed a bit (each tool now returns an exit code).

@changelog_1047_li
Command line help of the tools now match the javadocs.  The build converts the javadocs to a resource that is read by the tool at runtime.  This should not have an effect on using the database, but it reduces duplicate  and out-of-sync documentation.

@changelog_1048_li
CREATE TABLE: improved compatibility (support for UNIQUE NOT NULL).

@changelog_1049_li
DatabaseMetaData.getSQLKeywords now returns the correct list.

@changelog_1050_li
Deterministic user defined functions did not work when the parameter was a column. Fixed.

@changelog_1051_li
JdbcConnectionPool.setLoginTimeout with 0 now uses the default timeout.

@changelog_1052_li
Creating a JdbcConnectionPool has been simplified a bit.

@changelog_1053_li
The built-in connection pool did not re-use connections.  Getting a connection using the built-in JdbcConnectionPool is now about 70 times faster  than opening connections using DriverManager.getConnection.

@changelog_1054_li
More bugs in the server-less multi-connection mode have been fixed:  If a process terminated while writing, other open connections were blocked.  If two processes were writing to the database, sometimes the database was corrupt after closing.

@changelog_1055_li
Linked tables to SQLite database can now be created.

@changelog_1056_li
Nested IN(IN(...)) didn't work.

@changelog_1057_li
NIO storage: the nio: prefix was using memory mapped files instead of FileChannel.

@changelog_1058_h2
Version 1.1.109 (2009-03-14)

@changelog_1059_li
The optimization for IN(...) is now only used if comparing a column with an index.

@changelog_1060_li
User defined functions can now be deterministic (see CREATE ALIAS documentation).

@changelog_1061_li
Multiple nested queries in the FROM clause with parameters did not always work.

@changelog_1062_li
When converting CLOB to BINARY, each character resulted in one byte.  Now, the text is parsed as a hex as when converting VARCHAR.

@changelog_1063_li
New experimental NIO storage mechanism with both FileChannel and  memory mapped files. To use it, use the file name prefix nio: or nioMapped:  as in jdbc:h2:nio:~/test. So far it looks like NIO storage is faster on Mac OS  but slower on some Windows systems. Thanks a lot to Jan Kotek for the patch!

@changelog_1064_li
The functions BITOR, BITAND, BITXOR, and MOD now accept  and return BIGINT instead of INT.

@changelog_1065_li
Could not use the same linked table multiple times in the same query.

@changelog_1066_li
Bugs in the server-less multi-connection mode have been fixed.

@changelog_1067_li
Column names could not be named "UNIQUE" (with the quotes).

@changelog_1068_li
New system function TRANSACTION_ID() to get the current transaction  identifier for a session.

@changelog_1069_h2
Version 1.1.108 (2009-02-28)

@changelog_1070_li
When the shutdown hook closed the database, the last log file  was deleted too early. This could cause uncommitted changes to be persisted.  In some cases, this could cause data corruption.

@changelog_1071_li
JdbcConnectionPool: it was possible to set a negative connection pool size.

@changelog_1072_li
Fulltext search did not support table names with a backslash.

@changelog_1073_li
The internal IntArray class did not work correctly when initialized with a zero length array.

@changelog_1074_li
The H2 Console web application (war file) did only support ASCII characters.  Now UTF-8 is supported.

@changelog_1075_li
DATEADD does no longer require that the argument is a timestamp.

@changelog_1076_li
The database file locking mechanism didn't work correctly on Mac OS.

@changelog_1077_li
Some built-in functions reported the wrong precision, scale, and display size.

@changelog_1078_li
MySQL compatibility for CREATE TABLE is improved (UNSIGNED, KEY).

@changelog_1079_li
Recovery did not work if there were more than 255 lobs stored as files.

@changelog_1080_li
New experimental mode to support multiple read-write connections without starting  a server. To enable this mode, append ;FILE_LOCK=SERIALIZED;OPEN_NEW=TRUE to the database URL.  Don't expect high performance when multiple concurrent writers.

@changelog_1081_li
In a web application, the database classes are not unloaded if a connection is open.  This may cause out of memory when re-deploying a web application.  The DbStarter is changed to close all connections to the configured database  (by executing SHUTDOWN).

@changelog_1082_li
The WebServlet did not close the database when un-deploying the web application.

@changelog_1083_li
The exception message of failed INSERT or MERGE statements now includes all values and the row number.

@changelog_1084_li
If opening a database failed with an out of memory exception, some files were not closed.

@changelog_1085_li
Optimizer: the expected runtime calculation was incorrect. The fixed calculation  should give slightly better query plans when using many joins.

@changelog_1086_li
Improved exception message when connecting to a just started server fails.

@changelog_1087_li
Connection.isValid is a bit faster.

@changelog_1088_li
H2 Console: The autocomplete feature has been improved a bit. It can now better  parse conditions.

@changelog_1089_li
When restarting a web application in Tomcat, an exception was thrown sometimes.  In most cases this was a NullPointerException. A workaround in H2 has been implemented.  The root cause of the problem is now documented in the FAQ:  Tomcat sets all static fields (final or non-final) to null when unloading a web application.  A workaround is to put the h2.jar in the lib directory, or set the system property  org.apache.catalina.loader.WebappClassLoader.ENABLE_CLEAR_REFERENCES  to false.

@changelog_1090_h2
Version 1.1.107 (2009-01-24)

@changelog_1091_li
Some DatabaseMetaData operations did not work for non-admin users for versions 1.1.x.

@changelog_1092_li
The MySQL compatibility extension fromUnixTime now used the English locale.

@changelog_1093_li
When using LOG=2 and repeatedly updating the last row rows of a table, the index file grew quickly.

@changelog_1094_li
In versions 1.1.105 and 1.1.106, encrypted script files of earlier versions could not be processed.  This is now again possible. The problem was that such script files were stored in a special format  (STORAGE=TEXT) but support for this format was removed in version 1.1.105.

@changelog_1095_li
Enabling the trace mechanism by creating a specially named file is no longer supported.

@changelog_1096_h2
Version 1.1.106 (2009-01-04)

@changelog_1097_li
Statement.setQueryTimeout did not work correctly for some statements.

@changelog_1098_li
CREATE DOMAIN: Built-in data types can now only be changed if no tables exist.

@changelog_1099_li
Linked tables: a workaround for Oracle DATE columns has been implemented.

@changelog_1100_li
DatabaseMetaData.getPrimaryKeys: The column PK_NAME now contains the  constraint name instead of the index name (compatibility for PostgreSQL and Derby).

@changelog_1101_li
Using IN(..) inside a IN(SELECT..) did not always work.

@changelog_1102_li
Views with IN(..) that used a view itself did not work.

@changelog_1103_li
Union queries with LIMIT or ORDER BY that are used in a view or subquery did not work.

@changelog_1104_li
The license change a bit: so far the license was modified to say  'Swiss law'. This is now changed back to the original 'US law'.  This was requested by a user, and I don't see a problem.

@changelog_1105_li
Constraints for local temporary tables now session scoped. So far they were global.  Thanks a lot to Eric Faulhaber for finding and fixing this problem!

@changelog_1106_li
When using the auto-server mode, and if the lock file was modified in the future,  the wrong exception was thrown ('Connection is broken' instead of 'Error opening database: Lock file modified in the future').

@changelog_1107_h2
Version 1.1.105 (2008-12-19)

@changelog_1108_li
The setting STORAGE=TEXT is no longer supported.

@changelog_1109_li
Deleting a database using the tool DeleteDbFiles deleted LOB files  of other databases in the same directory.

@changelog_1110_li
When used in a subquery, LIKE and IN(..) did not work correctly sometimes.

@changelog_1111_li
The fulltext search documentation has been improved.

@changelog_1112_li
ARRAY_GET returned the wrong data type (ARRAY). Now it returns VARCHAR.

@changelog_1113_li
Natural join: the joined columns are not repeated any more when using SELECT *.

@changelog_1114_li
User defined aggregate functions: the method getType expected internal data types  instead of SQL types.

@changelog_1115_li
User defined aggregate functions did not work if there was no group by expression.

@changelog_1116_li
MySQL compatibility: support for := assignment as in @sum:=@sum+x

@changelog_1117_li
INSERT INTO TEST(SELECT * FROM TEST) is now supported.

@changelog_1118_li
Each session threw an invisible exception when garbage collected.

@changelog_1119_li
Foreign key constraints that refer to a quoted column did not work.

@changelog_1120_li
New meta data column INFORMATION_SCHEMA.TABLES.LAST_MODIFICATION to get  the table modification counter.

@changelog_1121_li
Shell: line comments didn't work correctly.

@changelog_1122_li
H2 Console: Columns are now listed for up to 500 tables instead of 100.

@changelog_1123_li
H2 Console: Cmd+Enter executes the current statement, Alt+Space for autocomplete.

@changelog_1124_li
JaQu: the maximum length of a column can now be defined using maxLength.  For an example, see Product.java (maxLength(category, 255)).

@changelog_1125_li
R&\#305;dvan A&\#287;ar has completed the Turkish translation of the H2 Console. Thanks a lot!

@changelog_1126_h2
Version 1.1.104 (2008-11-28)

@changelog_1127_li
If a query that was used like a table contained group by and was ordered by an expression that  is not in the column list, an exception was thrown.

@changelog_1128_li
JaQu: tables are now auto-created when running a query.

@changelog_1129_li
The optimizer had problems with function tables (for example CSVREAD and FTL_SEARCH).  A new system property h2.estimatedFunctionTableRows (default 1000) defines how many rows  can be expected in the table.

@changelog_1130_li
The function SUM could overflow when using large values. It returns now a data type that is safe.

@changelog_1131_li
The function AVG could overflow when using large values. Fixed.

@changelog_1132_li
The emergency reserve file has been removed. It didn't provide an appropriate  solution for the problem. It is still possible for an application to detect and deal with  the low disk space problem (deleting temporary files for example)  using DatabaseEventListener.diskSpaceIsLow, but this method is now always called  with stillAvailable=0.

@changelog_1133_li
Build: JAVA_HOME is now automatically detected on Mac OS X.

@changelog_1134_li
Testing for local connections was very slow on some systems.

@changelog_1135_li
The cache memory usage calculation is more conservative.

@changelog_1136_li
Allocating space got slower and slower the larger the database.

@changelog_1137_li
ALTER TABLE ALTER COLUMN could throw the wrong exception in the last version  (Table not found).

@changelog_1138_li
Updatable result sets: the key columns can now be updated.

@changelog_1139_li
The H2DatabaseProvider for ActiveObjects is now included in the tools section.

@changelog_1140_li
The H2Platform for Oracle Toplink Essential has been improved a bit.

@changelog_1141_li
The Windows service to start H2 didn't work in version 1.1.

@changelog_1142_li
File systems with a maximum file size (for example FAT) are now supported using  the file prefix 'split:'. In this case the files are split in parts of 1 GB.  Example URL: jdbc:h2:split:~/db/test. If you want to split into parts of 1 MB, use  jdbc:h2:split:20:~/db/test (the part size is 1 &lt;&lt; x, the default is 30 meaning 1 GB).

@changelog_1143_li
The database now tries to detect if the classloader or virtual machine has  almost shut down by checking if static final variables are set to null.  This should help reduce exceptions when stopping the web application.

@changelog_1144_li
Compatibility for MS SQL Server DATEDIFF(YYYY, .., ..)

@changelog_1145_li
ResultSet.getObject for CLOB or BLOB will return a java.sql.Clob / java.sql.Blob object instead of  a java.io.Reader / java.io.InputStream as in version 1.0. This behavior can be changed using the system  property h2.returnLobObjects (true by default for version 1.1).

@changelog_1146_li
The interface CloseListener has a new method 'remove' that is called when the trigger is dropped.

@changelog_1147_li
Fulltext search: there was a memory leak when creating and dropping fulltext indexes in a loop.

@changelog_1148_h2
Version 1.1.103 (2008-11-07)

@changelog_1149_li
Could not order by a formula when the formula was in the group by list  but not in the select list.

@changelog_1150_li
Date values that match the daylight saving time end were not allowed in  times zones were the daylight saving time ends at midnight, for years larger than 2037.  Example: timezone Brasilia, date 2042-10-12. This is a problem of Java, however a  workaround is implemented in H2 that solves most problems (except the problems of  java.util.Date itself).

@changelog_1151_li
ALTER TABLE used a lot of memory when using multi-version concurrency.

@changelog_1152_li
Referential integrity for in-memory databases didn't work in some cases in version 1.1.102.

@changelog_1153_li
New column INFORMATION_SCHEMA.COLUMNS.SEQUENCE_NAME to get the name  of the sequence for auto-increment columns.

@changelog_1154_li
Aliases for built-in data types (such as MEDIUMBLOB which is an alias for BLOB)  can now be re-mapped to another data type using CREATE DOMAIN. However  main built-in data types (such as INTEGER) can not be re-mapped.

@changelog_1155_li
The Japanese translation has been completed by Masahiro Ikemoto.  Thanks a lot!

@changelog_1156_li
Improved PostgreSQL compatibility for NEXTVAL and CURRVAL.

@changelog_1157_li
Less heap memory is needed when multiple databases are open at the same time: The memory reserve  (used to rollback after out of memory) is now global and no longer allocated for each database separately.

@changelog_1158_li
New system property h2.browser to set the browser to use.

@changelog_1159_li
To start the browser, java.awt.Desktop.browse is now used if available.

@changelog_1160_h2
Version 1.1.102 (2008-10-24)

@changelog_1161_li
The French translation of the H2 Console has been improved by Olivier Parent.  Thanks a lot!

@changelog_1162_li
There was a memory leak when creating and dropping tables and  indexes in a loop (persistent database only).

@changelog_1163_li
SET LOG 2 was not effective if executed after opening the database.

@changelog_1164_li
Translating the H2 Console is now simpler.

@changelog_1165_li
Common exception (error code 23*) are no longer written to the .trace.db file by default.

@changelog_1166_li
In-memory databases don't write LOBs to files any longer.

@changelog_1167_li
Self referencing constraints didn't restrict deleting rows that reference  itself if there is another row that references it.

@changelog_1168_li
ResultSetMetaData.getColumnName now returns the alias name except for columns.

@changelog_1169_li
Temporary files are now deleted when the database is closed, even  if they were not garbage collected so far.

@changelog_1170_h2
Version 1.1.101 (2008-10-17)

@changelog_1171_li
Errors with code 42000 - 42999 are no longer written to the trace file by default.

@changelog_1172_li
Queries with more than 10 tables are now faster.

@changelog_1173_li
Opening a connection with AUTO_SERVER=TRUE is now fast  when the database is already open in another process (less than 0.01 seconds  instead of 2 seconds).

@changelog_1174_li
IF [NOT] EXISTS is supported for named constraints in  ALTER TABLE ... ADD/DROP CONSTRAINT.

@changelog_1175_li
The error messages have been translated to Spanish by Dario V. Fassi.  Thanks a lot!

@changelog_1176_li
Linked tables: the automatic connection sharing didn't work. Actually the  system property h2.shareLinkedConnections was working in the opposite direction:  it was disabled when set to true. Now it works as expected.

@changelog_1177_li
Opening large database is now faster.

@changelog_1178_li
New system property h2.socketConnectTimeout, the timeout in milliseconds  to connect to a server. The default is 2000 (2 seconds).

@changelog_1179_li
The wrong parameters were bound to subqueries with parameters, specially  when using IN(SELECT ...) and IN(...).

@changelog_1180_li
Unset parameters were not detected when the query was re-compiled.

@changelog_1181_li
New functions ISO_YEAR, ISO_WEEK, ISO_DAY_OF_WEEK.  Thanks a lot to Robert Rathsack for implementing those!

@changelog_1182_li
The date functions DAYOFYEAR, DAYOFMONTH, DAYOFWEEK are now called  DAY_OF_YEAR, DAY_OF_MONTH, DAY_OF_WEEK (the old names still work).

@changelog_1183_li
An out of memory error while deleting or updating many rows could  result in a strange exception.

@changelog_1184_li
Linked tables: compatibility with MS SQL Server has been improved.

@changelog_1185_li
Renaming tables that have foreign keys with cascade didn't work correctly.

@changelog_1186_li
The auto-reconnect feature didn't work when using the auto-server mode. Fixed.

@changelog_1187_li
Fulltext search: new method FT_DROP_INDEX.

@changelog_1188_li
The optimization to group using an index didn't work in some cases in version 1.1  (see also system property h2.optimizeGroupSorted).

@changelog_1189_li
OSGi meta data is included in the manifest file.  An OSGi BundleActivator is included: it loads the database driver when starting the bundle,  and unloads it when stopping the bundle.

@changelog_1190_li
The default value for MAX_MEMORY_UNDO is now 50000.

@changelog_1191_li
For alias columns, ResultSetMetaData.getTableName() and getColumnName() now   return the real table and column name in the default mode.

@changelog_1192_li
In SQL scripts created with SCRIPT TO, schemas are now only created if they don't exist yet.

@changelog_1193_li
After re-connecting to a database, the database event listener (if set) is informed about it.

@changelog_1194_li
Local temporary tables now support indexes. Thanks a lot to Matt Roy!

@changelog_1195_li
RUNSCRIPT no longer uses a temporary file.

@changelog_1196_li
New system table INFORMATION_SCHEMA.SESSION_STATE containing the  SQL statements that make up the session state. The list currently contains  variables (SET @..) and local temporary tables (without data).

@changelog_1197_li
After an automatic re-connect, part of the session state stays (the part  that is stored in the SESSION_STATE table).

@changelog_1198_li
The build didn't work if the directory temp didn't exist before.

@changelog_1199_li
New system property h2.maxReconnect (default 3) to limit the number of re-connects  for the same SQL statement (this is usually only important for SHUTDOWN).

@changelog_1200_li
WHERE .. IN (SELECT ...) could throw a NullPointerException.

@changelog_1201_li
Improved Glassfish / Toplink support in H2Platform  thanks to Marcio Borges from Brazil. Thanks a lot!

@changelog_1202_h2
Version 1.1.100 (2008-10-04)

@changelog_1203_li
In version 1.1, the following system properties are now enabled by default:  h2.lobFilesInDirectories, h2.optimizeGroupSorted, h2.optimizeInJoin, h2.shareLinkedConnections

@changelog_1204_li
The H2 Console tool now works with the JDBC-ODBC bridge.

@changelog_1205_li
The H2 Console tool now supports command line options to start things separately.

@changelog_1206_li
Large objects did not work for in-memory databases in server mode in Linux.

@changelog_1207_li
Connections from a local address other than 'localhost' were not allowed if remote  connections were disabled. This was always a problem, but only got visible in the last release  because the server no longer connects to 'localhost' if networked.

@changelog_1208_li
The h2console.war can now be built using the Java build.

@changelog_1209_li
By default, databases are shared in the same process. For read-only databases  this causes unnecessary synchronization, but safes memory. If you want that each connection  opens its own database, append ;OPEN_NEW=TRUE to the database URL.

@changelog_1210_li
New auto-reconnect feature will cause the JDBC driver to reconnect to  the database if the connection is lost. To enable, append ;AUTO_RECONNECT=TRUE to the database URL.  This is specially helpful when using AUTO_SERVER. AUTO_SERVER automatically uses auto-reconnect.

@changelog_1211_li
CreateCluster: the property 'serverlist' is now called 'serverList'.

@changelog_1212_li
The ConvertTraceFile tool could not parse some files because the trace  mechanism did not encode prepared statement parameters.

@changelog_1213_li
Databases names can now be one character long  (the minimum size used to be 2 characters).

@changelog_1214_h2
Version 1.0.79 (2008-09-26)

@changelog_1215_li
Linked tables that point to the same database can now share the connection  within the same database. Access to the same connection is serialized. To enable this feature,  set the system property h2.shareLinkedConnections to true.

@changelog_1216_li
Multiple processes can now access the same database without having to explicitly  start the server. To do that, append ;AUTO_SERVER=TRUE to the database URL.  In this case, the server is started automatically if the connection is in embedded mode,  and the server mode is used if a server is running. If the process that opened the first  connection is closed, the other client need to reconnect (there is no automatic re-connect so far).  Remote connections are allowed, but only to this database.

@changelog_1217_li
The server tool now displays the correct IP address if networked.

@changelog_1218_li
Can now start a TCP server with port 0 (automatically select a port).

@changelog_1219_li
Result sets with just a unique index can now be updated (previously a primary key was required).

@changelog_1220_li
LINKED TABLE: the schema name can now be set. When multiple tables exist in different schema,  and the schema name is not set, an exception is thrown.

@changelog_1221_li
LINKED TABLE: worked around a bug in Oracle with the CHAR data type.

@changelog_1222_li
Faster hash code calculation for large binary arrays.

@changelog_1223_li
Faster storage re-use algorithm thanks to Greg Dhuse from cleversafe.com.

@changelog_1224_li
The database supports the SHOW command for better MySQL and PostgreSQL compatibility.

@changelog_1225_li
The H2 Console now abbreviates large texts in results.

@changelog_1226_li
Multiple UNION queries could not be used in derived tables.

@changelog_1227_li
Linked tables can now be read-only.

@changelog_1228_li
Temporary linked tables are now supported.

@changelog_1229_li
It was possible to create tables in read-only databases.

@changelog_1230_li
SET SCHEMA_SEARCH_PATH is now documented.

@changelog_1231_li
SET SCHEMA did not work for views.

@changelog_1232_li
Row level locking for MVCC is now enabled. The exception  'Concurrent update in table ...' is still thrown, but only after the lock timeout.

@changelog_1233_li
The maximum log file size setting was ignored for large databases.

@changelog_1234_li
Multi-Version Concurrency (MVCC) may no longer be used when using  the multi-threaded kernel feature (MULTI_THREADED). An exception is thrown  when trying to connect with both settings. Additional synchronization  is required before those features can be used together.

@changelog_1235_li
The data type JAVA_OBJECT could not be used in updatable result sets.

@changelog_1236_li
The system property h2.optimizeInJoin did not work correctly.

@changelog_1237_li
Conditions such as ID=? AND ID>? were slow.

@changelog_1238_h2
Version 1.0.78 (2008-08-28)

@changelog_1239_li
The documentation no longer uses a frameset (except the Javadocs).

@changelog_1240_li
When using DB_CLOSE_DELAY, sometimes a NullPointerException is thrown when  the database is opened almost at the same time as it is closed automatically.  Thanks a lot to Dmitry Pekar for finding this!

@changelog_1241_li
Java methods with variable number of parameters can now be used (for Java 1.5 or newer).

@changelog_1242_li
The Japanese translation has been improved by Masahiro Ikemoto. Thanks a lot!

@changelog_1243_li
The H2 Console replaced an empty user name with a single space.

@changelog_1244_li
The build target 'build jarSmall' now includes the embedded database.

@changelog_1245_li
JdbcDataSource now keeps the password in a char array where possible.

@changelog_1246_li
ResultSet.absolute did not always work with large result sets.

@changelog_1247_li
Column aliases can now be used in GROUP BY and HAVING.

@changelog_1248_li
Jason Brittain has contributed MySQL date functions. Thanks a lot!  They are not in the h2.jar file currently, but in src/tools/org/h2/mode/FunctionsMySQL.java.  To install, add this class to the classpath and call FunctionsMySQL.register(conn) in the Java code.

@changelog_1249_h2
Version 1.0.77 (2008-08-16)

@changelog_1250_li
JaQu is now using prepared statements and supports Date, Time, Timestamp.

@changelog_1251_li
When using remote in-memory databases, large LOB objects did not work.

@changelog_1252_li
Timestamp columns such as TIMESTAMP(6) were not compatible to other database.

@changelog_1253_li
Opening a large database was slow if there was a problem opening the previous time.

@changelog_1254_li
NOT IN(SELECT ...) was incorrect if the subquery returns no rows.

@changelog_1255_li
CREATE TABLE AS SELECT did not work correctly in the multi-version concurrency mode.

@changelog_1256_li
Support a comma before closing a list, as in: create table test(id int,)

@changelog_1257_li
MySQL compatibility: linked tables had lower case column names on some systems.

@changelog_1258_li
DB2 compatibility: the DB2 fetch-first-clause is supported.

@changelog_1259_li
Oracle compatibility: old style outer join syntax using (+) did work correctly sometimes.

@changelog_1260_li
ResultSet.setFetchSize is now supported.

@changelog_1261_li
It has been reported that when using Install4j on some Linux systems and enabling the 'pack200' option,  the h2.jar becomes corrupted by the install process, causing application failure.  A workaround is to add an empty file h2.jar.nopack next to the h2.jar file.  The reason for this problem is not known.

@changelog_1262_h2
Version 1.0.76 (2008-07-27)

@changelog_1263_li
The comment of a domain (user defined data type) is now used as the  default column comment when creating a column with this domain.

@changelog_1264_li
Invalid database names are now detected and a better error message is thrown.

@changelog_1265_li
ResultSetMetaData.getColumnClassName now returns the correct  class name for BLOB and CLOB.

@changelog_1266_li
Fixed the Oracle mode: Oracle allows multiple rows only where  all columns of the unique index are NULL.

@changelog_1267_li
There is a problem with Hibernate when using Boolean columns.  A patch for Hibernate has been submitted at  http://opensource.atlassian.com/projects/hibernate/browse/HHH-3401

@changelog_1268_li
ORDER BY on tableName.columnName didn't work correctly if the column  name was also used as an alias.

@changelog_1269_li
H2 Console: The progress display when opening a database has been improved.

@changelog_1270_li
The error message when the server doesn't start has been improved.

@changelog_1271_li
Key values can now be changed in updatable result sets.

@changelog_1272_li
Changes in updatable result sets are now visible even when resetting the result set.

@changelog_1273_li
Temporary files were sometimes deleted too late when executing large insert, update,  or delete operations.

@changelog_1274_li
The database file was growing after deleting many rows, and after large update operations.

@changelog_1275_h2
Version 1.0.75 (2008-07-14)

@changelog_1276_li
Multi version concurrency (MVCC): when a row was updated or deleted, but this change was rolled back,  the row was not visible by other sessions if no index was used to access it. Fixed.

@changelog_1277_li
Views with multiple joined tables (where one was an outer join) couldn't be used in some cases. Fixed.

@changelog_1278_li
The CSVREAD method did not process NULL correctly when using a whitespace field separator.

@changelog_1279_li
Fixed the Oracle mode: Oracle allows multiple rows with NULL in a unique index.

@changelog_1280_li
Running out of memory could result in incomplete transactions or corrupted databases. Fixed.

@changelog_1281_li
When using order by in a query that uses the same table multiple times, the order could  be incorrect. Fixed.

@changelog_1282_li
Referential constraint checking improvement: now the constraint is only checked  if the key column values change.

@changelog_1283_li
Some database metadata calls returned the wrong data type for DATA_TYPE columns.

@changelog_1284_li
The Lucene fulltext index was empty when opening a database with fulltext  index enabled, and re-indexing it didn't work. Fixed.

@changelog_1285_li
The character '$' could not be used in identifier names (table name,  column names and so on). Fixed.

@changelog_1286_li
The new method org.h2.tools.Server.startWebServer(conn) starts the H2 Console  to inspect a database while debugging.

@changelog_1287_li
Stopping a WebServer didn't always work. Fixed.

@changelog_1288_h2
Version 1.0.74 (2008-06-21)

@changelog_1289_li
Work on row level locking has been started (but there is nothing usable yet).

@changelog_1290_li
JaQu (Java Query), a tool similar to LINQ (Language Integrated Query; from Microsoft)  is now included under src/tools/org/h2/jaqu. A small sample application is included under  src/test/org/h2/test/jaqu.

@changelog_1291_li
The source code is now switched to Java 1.6 by default. To switch back to Java 1.4, run 'build compile'.  The h2.jar file is still Java 1.4.

@changelog_1292_li
The ChangePassword tool is now called ChangeFileEncryption.

@changelog_1293_li
It is no longer allowed to create columns with the data type NULL.  Also, it is no longer allowed to convert a column to the data type NULL.  This was possible before but caused data loss.

@changelog_1294_li
When using computed columns or default values with a different data type than the column data type,  a class cast exception could occur. Fixed.

@changelog_1295_li
Opening databases larger than 1 GB was sometimes very slow if a lot of data was deleted previously. Fixed.

@changelog_1296_li
RUNSCRIPT could throw a NullPointerException if the script name was an expression.

@changelog_1297_li
Improved compatibility. New compatibility modes for Oracle and Derby.  New compatibility flag uniqueIndexNullDistinct to only allow one row with 'NULL' in a unique  index. This flag is enabled for Derby, Oracle, MSSQLServer, and HSQLDB.

@changelog_1298_li
Linked tables: To view the statements that are executed against the target table, set the trace level to 3.

@changelog_1299_li
RunScript tool: new options to show and check the results of queries.

@changelog_1300_li
Deadlocks are now detected. One transaction is rolled back automatically.

@changelog_1301_li
The Lucene fulltext index was always re-created when opening a  database with fulltext index enabled.

@changelog_1302_li
Support for overloaded Java methods. A user defined function can  now be bound to multiple Java methods, if the Java methods have the same  name but a different number of parameters. Thanks to Gary Tong for  providing a patch!

@changelog_1303_h2
Version 1.0.73 (2008-05-31)

@changelog_1304_li
ParameterMetaData now returns the right data type for most   conditions, as in WHERE ID=?.

@changelog_1305_li
The table SYSTEM_RANGE now supports expressions and parameters.

@changelog_1306_li
New column INFORMATION_SCHEMA.CONSTRAINTS.UNIQUE_INDEX_NAME   that contains the name of the unique index used to enforce this   constraint, if there is such an index.

@changelog_1307_li
SET QUERY_TIMEOUT and Statement.setQueryTimeout no longer commits   a transaction. The same applies to SET @VARIABLE, SET LOCK_TIMEOUT,   SET TRACE_LEVEL_*, SET THROTTLE, and SET PATH.

@changelog_1308_li
The SCRIPT command does now emit IF NOT EXISTS for CREATE ROLE.

@changelog_1309_li
MySQL compatibility: auto_increment column are no longer automatically   converted to primary key columns.

@changelog_1310_li
PostgreSQL compatibility: support for BOOL_OR and BOOL_AND   aggregate functions.

@changelog_1311_li
Negative scale values for DECIMAL or NUMBER columns are now supported   in regular tables and in linked tables.

@changelog_1312_li
A role or right can now be granted or revoked multiple times without   getting an exception.

@changelog_1313_li
Infinite numbers in SQL scripts are listed as POWER(0, -1)), negative   infinite as (-POWER(0, -1)), and NaN (not a number) as SQRT(-1).

@changelog_1314_li
The special double and float values 'NaN' (not a number) did not work   correctly when sorting or comparing.

@changelog_1315_li
The fulltext search did not support CLOB data types.

@changelog_1316_li
If the drive with the database files was disconnected or unmounted   while writing, sometimes a stack overflow exception was thrown   instead of a IO exception.

@changelog_1317_li
The H2 Console could not be shut down from within the tool if the   browser supports keepAlive (most browsers do).

@changelog_1318_li
If the password was passed as a char array, it was kept in an internal buffer   longer than required. Theoretically the password could have been stolen   if the main memory was swapped to disk before the garbage collection was run.

@changelog_1319_h2
Version 1.0.72 (2008-05-10)

@changelog_1320_li
Some databases could not be opened when appending   ;RECOVER=1 to the database URL.

@changelog_1321_li
The Japanese translation of the error messages and the H2 Console   has been completed by Masahiro Ikemoto (Arizona Design Inc.)

@changelog_1322_li
Updates made to updatable rows are now visible within the same result set.   DatabaseMetaData.ownUpdatesAreVisible now returns true.

@changelog_1323_li
ParameterMetaData now returns the correct data   for INSERT and UPDATE statements.

@changelog_1324_li
H2 Shell: DESCRIBE now supports an schema name.

@changelog_1325_li
A subset of the PostgreSQL 'dollar quoting' feature is now supported.

@changelog_1326_li
SLF4J is now supported by using adding TRACE_LEVEL_FILE=4   to the database URL.

@changelog_1327_li
The recovery tool did not work if the table name contained spaces   or if there was a comment on the table.

@changelog_1328_li
Triggers are no longer executed when changing the table   structure (ALTER TABLE).

@changelog_1329_li
When setting BLOB or CLOB values larger than 65 KB using   a remote connection, temporary files were kept on the client   longer than required (until the connection was closed or the   object is garbage collected). Now they are removed as soon   as the PreparedStatement is closed, or when the value is   overwritten.

@changelog_1330_li
Statements can now be canceled remotely   (when using remote connections).

@changelog_1331_li
The Shell tool now uses java.io.Console to read the password   when using JDK 1.6

@changelog_1332_li
When using read-only databases and setting LOG=2, an exception   was written to the trace file when closing the database. Fixed.

@changelog_1333_h2
Version 1.0.71 (2008-04-25)

@changelog_1334_li
H2 is now dual-licensed under the Eclipse Public License (EPL) and the  old 'H2 License' (which is basically MPL).

@changelog_1335_li
Sometimes an exception 'File ID mismatch' or 'try to add a record twice'  occurred after large records (8 KB or larger) are updated or deleted.  See also http://code.google.com/p/h2database/issues/detail?id=22

@changelog_1336_li
H2 Console: The tools can now be translated  (it didn't work in the last release).

@changelog_1337_li
New traditional Chinese translation. Thanks a lot to Derek Chao!

@changelog_1338_li
Indexes were not used when enabling the optimization for  IN(SELECT...) (system property h2.optimizeInJoin).

@changelog_1339_h2
Version 1.0.70 (2008-04-20)

@changelog_1340_li
The plan is to dual-license H2. The additional license is EPL (Eclipse Public License).  The current license (MPL, Mozilla Public License) will stay.  Current users are not affected because they can keep MPL.  EPL is very similar to MPL, the only bigger difference is related to patents  (EPL is a bit more business friendly in this regard).  See also http://opensource.org/licenses/eclipse-1.0.php,  http://www.eclipse.org/legal/eplfaq.php (FAQ),  http://blogs.zdnet.com/Burnette/?p=131

@changelog_1341_li
Multi version concurrency (MVCC): when a row was updated,  and the updated column was not indexed, this update was visible sometimes  for other sessions even if it was not committed.

@changelog_1342_li
Calling SHUTDOWN on one connection and starting a query on  another connection concurrently could result in a Java level deadlock.

@changelog_1343_li
New system property h2.enableAnonymousSSL (default: true) to enable  anonymous SSL connections.

@changelog_1344_li
The precision if SUBSTR is now calculated if possible.

@changelog_1345_li
The autocomplete in the H2 Console has been improved a bit.

@changelog_1346_li
The tools in the H2 Console are now translatable.

@changelog_1347_li
The servlet and lucene jar files are now automatically downloaded when building.

@changelog_1348_li
The code switch tool has been replaced by a simpler tool called  SwitchSource that just uses find and replace.

@changelog_1349_li
Started to write a Ant replacement ('JAnt') that uses pure Java  build definitions. Advantages: ability to debug the build, extensible,  flexible, no XML, a bit faster. Future plan: support creating custom h2  distributions (for embedded use). Maybe create a new project 'Jant'  or 'Javen' if other people are interested.

@changelog_1350_li
The jar file is now about 10% smaller because the variable debugging info  is no longer included. The source file and line number debugging info  is still included. If required, the jar file size of the full version can  be further reduced to about 720 KB using 'build jarSmall' or even  more by removing unneeded components.

@changelog_1351_li
Added shell scripts run.sh and build.sh. chmod +x is required,  but otherwise it should work. Feedback or improvements are welcome!

@changelog_1352_li
Databases in zip files: large queries are now supported. Temp files are created in  the temp directory if required. The documentation how to create  the zip file has been corrected.

@changelog_1353_li
Invalid inline views threw confusing SQL exceptions.

@changelog_1354_li
The Japanese translation of the error messages and the  H2 Console has been improved. Thanks a lot to Masahiro IKEMOTO.

@changelog_1355_li
Optimization for MIN() and MAX() when using MVCC.

@changelog_1356_li
To protect against remote brute force password attacks,  the delay after each unsuccessful login now gets double as long.  New system properties h2.delayWrongPasswordMin  and h2.delayWrongPasswordMax.

@changelog_1357_li
After setting the query timeout and then resetting it, the next query  would still timeout. Fixed.

@changelog_1358_li
Adding a IDENTITY column to a table with data threw a lock timeout.

@changelog_1359_li
OutOfMemoryError could occur when using EXISTS or IN(SELECT ..).

@changelog_1360_li
The built-in connection pool is not called JdbcConnectionPool.  The API and documentation has been changed.

@changelog_1361_li
The ConvertTraceFile tool now generates SQL statement statistics  at the end of the SQL script file (similar to the profiling data  generated when using java -Xrunhprof).

@changelog_1362_li
Nested joins are now supported (A JOIN B JOIN C ON .. ON ..)

@download_1000_h1
Downloads

@download_1001_h3
Version 1.1.113 (2009-05-21)

@download_1002_a
Windows Installer

@download_1003_a
Platform-Independent Zip

@download_1004_h3
Version 1.1.112 (2009-05-01, Last Stable)

@download_1005_a
Windows Installer

@download_1006_a
Platform-Independent Zip

@download_1007_h3
Download Mirror and Older Versions

@download_1008_a
Platform-Independent Zip

@download_1009_h3
Jar File

@download_1010_a
Maven.org

@download_1011_a
Sourceforge.net

@download_1012_a
Latest Automated Build (not released)

@download_1013_h3
Subversion Source Repository

@download_1014_a
Google Code

@download_1015_p
For details about changes, see the <a href="changelog.html">Change Log</a> .

@faq_1000_h1
Frequently Asked Questions

@faq_1001_a
Are there Known Bugs? When is the Next Release?

@faq_1002_a
Is this Database Engine Open Source?

@faq_1003_a
My Query is Slow

@faq_1004_a
How to Create a New Database?

@faq_1005_a
How to Connect to a Database?

@faq_1006_a
Where are the Database Files Stored?

@faq_1007_a
What is the Size Limit (Maximum Size) of a Database?

@faq_1008_a
Is it Reliable?

@faq_1009_a
Why is Opening my Database Slow?

@faq_1010_a
Is the GCJ Version Stable? Faster?

@faq_1011_a
How to Translate this Project?

@faq_1012_h3
Are there Known Bugs? When is the Next Release?

@faq_1013_p
Usually, bugs get fixes as they are found. There is a release every few weeks. Here is the list of known and confirmed issues:

@faq_1014_li
Tomcat and Glassfish 3 set most static fields (final or non-final) to null when  unloading a web application. This can cause a NullPointerException in H2 versions  1.1.107 and older, and may still not work in newer versions. Please report it if you  run into this issue. In Tomcat >= 6.0 this behavior can be disabled by setting the  system property org.apache.catalina.loader.WebappClassLoader.ENABLE_CLEAR_REFERENCES  to false, however Tomcat may then run out of memory. A known workaround is to  put the h2.jar file in a shared <code>lib</code> directory (common/lib).

@faq_1015_li
Some problems have been found with right outer join. Internally, it is converted  to left outer join, which does not always produce the same results as other databases  when used in combination with other joins.

@faq_1016_li
When using Install4j before 4.1.4 on Linux and enabling 'pack200',  the h2*.jar becomes corrupted by the install process, causing application failure.  A workaround is to add an empty file h2*.jar.nopack next to the h2*.jar file.  This problem is solved in Install4j 4.1.4.

@faq_1017_h3
Is this Database Engine Open Source?

@faq_1018_p
Yes. It is free to use and distribute, and the source code is included. See also under license.

@faq_1019_h3
My Query is Slow

@faq_1020_p
Slow SELECT (or DELETE, UPDATE, MERGE) statement can have multiple reasons. Follow this checklist:

@faq_1021_li
Run ANALYZE (see documentation for details).

@faq_1022_li
Run the query with EXPLAIN and check if indexes are used (see documentation for details).

@faq_1023_li
If required, create additional indexes and try again using ANALYZE and EXPLAIN.

@faq_1024_li
If it doesn't help please report the problem.

@faq_1025_h3
How to Create a New Database?

@faq_1026_p
By default, a new database is automatically created if it does not yet exist.

@faq_1027_h3
How to Connect to a Database?

@faq_1028_p
The database driver is <code>org.h2.Driver</code> , and the database URL starts with <code>jdbc:h2:</code> . To connect to a database using JDBC, use the following code:

@faq_1029_h3
Where are the Database Files Stored?

@faq_1030_p
When using database URLs like jdbc:h2:~/test, the database is stored in the user directory. For Windows, this is usually "C:\Documents and Settings\&lt;userName&gt;". If the base directory is not set (as in jdbc:h2:test), the database files are stored in the directory where the application is started (the current working directory). When using the H2 Console application from the start menu, this is "&lt;Installation Directory&gt;/bin". The base directory can be set in the database URL. A fixed or relative path can be used. When using the URL jdbc:h2:file:data/sample, the database is stored in the directory "data" (relative to the current working directory). The directory is created automatically if it does not yet exist. It is also possible to use the fully qualified directory name (and for Windows, drive name). Example: jdbc:h2:file:C:/data/test

@faq_1031_h3
What is the Size Limit (Maximum Size) of a Database?

@faq_1032_p
The theoretical limit is currently 256 GB for the data. This number is excluding BLOB and CLOB data: every CLOB or BLOB can be up to 256 GB as well. The size limit of the index data is 256 GB as well.

@faq_1033_p
The maximum number of rows per table is 2'147'483'648.

@faq_1034_p
The maximum file size for FAT or FAT32 file systems is usually 4 GB. The database does provide a workaround for this problem, it is to use the file name prefix 'split:'. See also Advanced / Limitations.

@faq_1035_p
The larger the database, the more main memory is required. Currently the minimum main memory required for a 12 GB database is around 240 MB.

@faq_1036_h3
Is it Reliable?

@faq_1037_p
That is not easy to say. It is still a quite new product. A lot of tests have been written, and the code coverage of these tests is very high. Randomized stress tests are run regularly. But there are probably still bug that have not yet been found (as with most software). Some features are known to be dangerous, they are only supported for situations where performance is more important than reliability. Those dangerous features are:

@faq_1038_li
Disabling the transaction log mechanism using SET LOG 0.

@faq_1039_li
Using the transaction isolation level READ_UNCOMMITTED (LOCK_MODE 0) while at the same time using multiple  connections.

@faq_1040_li
Disabling database file protection using FILE_LOCK=NO in the database URL.

@faq_1041_li
Disabling referential integrity using SET REFERENTIAL_INTEGRITY FALSE.

@faq_1042_p
In addition to that, running out of memory should be avoided. In older versions, OutOfMemory errors while using the database could corrupt a databases.

@faq_1043_p
Areas that are not fully tested:

@faq_1044_li
Platforms other than Windows XP, Linux, Mac OS X, or JVMs other than Sun 1.4 - 1.6

@faq_1045_li
The features AUTO_SERVER and AUTO_RECONNECT

@faq_1046_li
The MVCC (multi version concurrency) mode

@faq_1047_li
Cluster mode, 2-phase commit, savepoints

@faq_1048_li
24/7 operation

@faq_1049_li
Some operations on databases larger than 500 MB may be slower than expected

@faq_1050_li
The optimizer may not always select the best plan

@faq_1051_p
Areas considered Experimental:

@faq_1052_li
The PostgreSQL server

@faq_1053_li
Compatibility modes for other databases (only some features are implemented)

@faq_1054_h3
Why is Opening my Database Slow?

@faq_1055_p
If it takes a long time to open a database, in most cases it was not closed the last time. This is specially a problem for larger databases. To close a database, close all connections to it before the application ends, or execute the command SHUTDOWN. The database is also closed when the virtual machine exits normally by using a shutdown hook. However killing a Java process or calling Runtime.halt will prevent this. The reason why opening is slow in this situations is that indexes are re-created. If you can not guarantee the database is closed, consider using SET LOG 2 (see SQL Grammar).

@faq_1056_p
To find out what the problem is, open the database in embedded mode using the H2 Console. This will print progress information. If you have many 'Creating index' lines it is an indication that the database was not closed the last time.

@faq_1057_p
Other possible reasons are: the database is very big (many GB), or contains linked tables that are slow to open.

@faq_1058_h3
Is the GCJ Version Stable? Faster?

@faq_1059_p
The GCJ version is not as stable as the Java version. When running the regression test with the GCJ version, sometimes the application just stops at what seems to be a random point without error message. Currently, the GCJ version is also slower than when using the Sun VM. However, the startup of the GCJ version is faster than when using a VM.

@faq_1060_h3
How to Translate this Project?

@faq_1061_p
For more information, see <a href="build.html#translating">Build/Translating</a> .

@features_1000_h1
Features

@features_1001_a
Feature List

@features_1002_a
Limitations

@features_1003_a
Comparison to Other Database Engines

@features_1004_a
H2 in Use

@features_1005_a
Connection Modes

@features_1006_a
Database URL Overview

@features_1007_a
Connecting to an Embedded (Local) Database

@features_1008_a
Memory-Only Databases

@features_1009_a
Database Files Encryption

@features_1010_a
Database File Locking

@features_1011_a
Opening a Database Only if it Already Exists

@features_1012_a
Closing a Database

@features_1013_a
Ignore Unknown Settings

@features_1014_a
Changing Other Settings when Opening a Connection

@features_1015_a
Log Index Changes

@features_1016_a
Custom File Access Mode

@features_1017_a
Multiple Connections

@features_1018_a
Database File Layout

@features_1019_a
Logging and Recovery

@features_1020_a
Compatibility

@features_1021_a
Auto-Reconnect

@features_1022_a
Automatic Mixed Mode

@features_1023_a
Using the Trace Options

@features_1024_a
Using Other Logging APIs

@features_1025_a
Read Only Databases

@features_1026_a
Read Only Databases in Zip or Jar File

@features_1027_a
Graceful Handling of Low Disk Space Situations

@features_1028_a
Computed Columns / Function Based Index

@features_1029_a
Multi-Dimensional Indexes

@features_1030_a
Using Passwords

@features_1031_a
User-Defined Functions and Stored Procedures

@features_1032_a
Triggers

@features_1033_a
Compacting a Database

@features_1034_a
Cache Settings

@features_1035_h2
Feature List

@features_1036_h3
Main Features

@features_1037_li
Very fast database engine

@features_1038_li
Open source

@features_1039_li
Written in Java

@features_1040_li
Supports standard SQL, JDBC API

@features_1041_li
Embedded and Server mode, Clustering support

@features_1042_li
Strong security features

@features_1043_li
The PostgreSQL ODBC driver can be used

@features_1044_li
Multi version concurrency

@features_1045_h3
Additional Features

@features_1046_li
Disk based or in-memory databases and tables, read-only database support, temporary tables

@features_1047_li
Transaction support (read committed and serializable transaction isolation), 2-phase-commit

@features_1048_li
Multiple connections, table level locking

@features_1049_li
Cost based optimizer, using a genetic algorithm for complex queries, zero-administration

@features_1050_li
Scrollable and updatable result set support, large result set, external result sorting, functions can return a result set

@features_1051_li
Encrypted database (AES or XTEA), SHA-256 password encryption, encryption functions, SSL

@features_1052_h3
SQL Support

@features_1053_li
Support for multiple schemas, information schema

@features_1054_li
Referential integrity / foreign key constraints with cascade, check constraints

@features_1055_li
Inner and outer joins, subqueries, read only views and inline views

@features_1056_li
Triggers and Java functions / stored procedures

@features_1057_li
Many built-in functions, including XML and lossless data compression

@features_1058_li
Wide range of data types including large objects (BLOB/CLOB) and arrays

@features_1059_li
Sequence and autoincrement columns, computed columns (can be used for function based indexes)

@features_1060_li
ORDER BY, GROUP BY, HAVING, UNION, LIMIT, TOP

@features_1061_li
Collation support, users, roles

@features_1062_li
Compatibility modes for IBM DB2, Apache Derby, HSQLDB, MS SQL Server, MySQL, Oracle, and PostgreSQL.

@features_1063_h3
Security Features

@features_1064_li
Includes a solution for the SQL injection problem

@features_1065_li
User password authentication uses SHA-256 and salt

@features_1066_li
For server mode connections, user passwords are never transmitted in plain text over the network (even when using insecure connections; this only applies to the TCP server and not to the H2 Console however; it also doesn't apply if you set the password in the database URL)

@features_1067_li
All database files (including script files that can be used to backup data) can be encrypted using AES-256 and XTEA encryption algorithms

@features_1068_li
The remote JDBC driver supports TCP/IP connections over SSL/TLS

@features_1069_li
The built-in web server supports connections over SSL/TLS

@features_1070_li
Passwords can be sent to the database using char arrays instead of Strings

@features_1071_h3
Other Features and Tools

@features_1072_li
Small footprint (smaller than 1 MB), low memory requirements

@features_1073_li
Multiple index types (b-tree, tree, hash)

@features_1074_li
Support for multi-dimensional indexes

@features_1075_li
CSV (comma separated values) file support

@features_1076_li
Support for linked tables, and a built-in virtual 'range' table

@features_1077_li
EXPLAIN PLAN support, sophisticated trace options

@features_1078_li
Database closing can be delayed or disabled to improve the performance

@features_1079_li
Web-based Console application (translated to many languages) with autocomplete

@features_1080_li
The database can generate SQL script files

@features_1081_li
Contains a recovery tool that can dump the contents of the database

@features_1082_li
Support for variables (for example to calculate running totals)

@features_1083_li
Automatic re-compilation of prepared statements

@features_1084_li
Uses a small number of database files

@features_1085_li
Uses a checksum for each record and log entry for data integrity

@features_1086_li
Well tested (high code coverage, randomized stress tests)

@features_1087_h2
Limitations

@features_1088_p
For the list of limitations, please have a look at the road map page at: <a href="http://www.h2database.com/html/roadmap.html">http://www.h2database.com/html/roadmap.html</a>

@features_1089_h2
Comparison to Other Database Engines

@features_1090_th
Feature

@features_1091_th
H2

@features_1092_a
Derby

@features_1093_a
HSQLDB

@features_1094_a
MySQL

@features_1095_a
PostgreSQL

@features_1096_td
Pure Java

@features_1097_td
Yes

@features_1098_td
Yes

@features_1099_td
Yes

@features_1100_td
No

@features_1101_td
No

@features_1102_td
Embedded Mode (Java)

@features_1103_td
Yes

@features_1104_td
Yes

@features_1105_td
Yes

@features_1106_td
No

@features_1107_td
No

@features_1108_td
Performance (Embedded)

@features_1109_td
Fast

@features_1110_td
Slow

@features_1111_td
Fast

@features_1112_td
N/A

@features_1113_td
N/A

@features_1114_td
In-Memory Mode

@features_1115_td
Yes

@features_1116_td
No

@features_1117_td
Yes

@features_1118_td
No

@features_1119_td
No

@features_1120_td
Transaction Isolation

@features_1121_td
Yes

@features_1122_td
Yes

@features_1123_td
No

@features_1124_td
Yes

@features_1125_td
Yes

@features_1126_td
Cost Based Optimizer

@features_1127_td
Yes

@features_1128_td
Yes

@features_1129_td
No

@features_1130_td
Yes

@features_1131_td
Yes

@features_1132_td
Explain Plan

@features_1133_td
Yes

@features_1134_td
No

@features_1135_td
Yes

@features_1136_td
Yes

@features_1137_td
Yes

@features_1138_td
Clustering

@features_1139_td
Yes

@features_1140_td
No

@features_1141_td
No

@features_1142_td
Yes

@features_1143_td
Yes

@features_1144_td
Encrypted Database

@features_1145_td
Yes

@features_1146_td
Yes

@features_1147_td
No

@features_1148_td
No

@features_1149_td
No

@features_1150_td
Linked Tables

@features_1151_td
Yes

@features_1152_td
No

@features_1153_td
Partially *1

@features_1154_td
Partially *2

@features_1155_td
No

@features_1156_td
ODBC Driver

@features_1157_td
Yes

@features_1158_td
No

@features_1159_td
No

@features_1160_td
Yes

@features_1161_td
Yes

@features_1162_td
Fulltext Search

@features_1163_td
Yes

@features_1164_td
No

@features_1165_td
No

@features_1166_td
Yes

@features_1167_td
Yes

@features_1168_td
User-Defined Datatypes

@features_1169_td
Yes

@features_1170_td
No

@features_1171_td
No

@features_1172_td
Yes

@features_1173_td
Yes

@features_1174_td
Files per Database

@features_1175_td
Few

@features_1176_td
Many

@features_1177_td
Few

@features_1178_td
Many

@features_1179_td
Many

@features_1180_td
Table Level Locking

@features_1181_td
Yes

@features_1182_td
Yes

@features_1183_td
No

@features_1184_td
Yes

@features_1185_td
Yes

@features_1186_td
Row Level Locking

@features_1187_td
Yes *9

@features_1188_td
Yes

@features_1189_td
No

@features_1190_td
Yes

@features_1191_td
Yes

@features_1192_td
Multi Version Concurrency

@features_1193_td
Yes

@features_1194_td
No

@features_1195_td
No

@features_1196_td
No

@features_1197_td
Yes

@features_1198_td
Role Based Security

@features_1199_td
Yes

@features_1200_td
Yes *3

@features_1201_td
Yes

@features_1202_td
Yes

@features_1203_td
Yes

@features_1204_td
Updatable Result Sets

@features_1205_td
Yes

@features_1206_td
Yes *7

@features_1207_td
No

@features_1208_td
Yes

@features_1209_td
Yes

@features_1210_td
Sequences

@features_1211_td
Yes

@features_1212_td
No

@features_1213_td
Yes

@features_1214_td
No

@features_1215_td
Yes

@features_1216_td
Limit and Offset

@features_1217_td
Yes

@features_1218_td
No

@features_1219_td
Yes

@features_1220_td
Yes

@features_1221_td
Yes

@features_1222_td
Temporary Tables

@features_1223_td
Yes

@features_1224_td
Yes *4

@features_1225_td
Yes

@features_1226_td
Yes

@features_1227_td
Yes

@features_1228_td
Information Schema

@features_1229_td
Yes

@features_1230_td
No *8

@features_1231_td
No *8

@features_1232_td
Yes

@features_1233_td
Yes

@features_1234_td
Computed Columns

@features_1235_td
Yes

@features_1236_td
No

@features_1237_td
No

@features_1238_td
No

@features_1239_td
Yes *6

@features_1240_td
Case Insensitive Columns

@features_1241_td
Yes

@features_1242_td
No

@features_1243_td
Yes

@features_1244_td
Yes

@features_1245_td
Yes *6

@features_1246_td
Custom Aggregate Functions

@features_1247_td
Yes

@features_1248_td
No

@features_1249_td
No

@features_1250_td
Yes

@features_1251_td
Yes

@features_1252_td
Footprint (jar/dll size)

@features_1253_td
~1 MB *5

@features_1254_td
~2 MB

@features_1255_td
~600 KB

@features_1256_td
~4 MB

@features_1257_td
~6 MB

@features_1258_p
*1 HSQLDB supports text tables.

@features_1259_p
*2 MySQL supports linked MySQL tables under the name 'federated tables'.

@features_1260_p
*3 Derby support for roles based security and password checking as an option.

@features_1261_p
*4 Derby only supports global temporary tables.

@features_1262_p
*5 The default H2 jar file contains debug information, jar files for other databases do not.

@features_1263_p
*6 PostgreSQL supports functional indexes.

@features_1264_p
*7 Derby only supports updatable result sets if the query is not sorted.

@features_1265_p
*8 Derby and HSQLDB don't support standard compliant information schema tables.

@features_1266_p
*9 H2 supports row level locks when using multi version concurrency.

@features_1267_h3
Derby and HSQLDB

@features_1268_p
After an unexpected process termination (for example power failure), H2 can recover safely and automatically without any user interaction. For Derby and HSQLDB, some manual steps are required ('Another instance of Derby may have already booted the database' / 'The database is already in use by another process').

@features_1269_h3
DaffodilDb and One$Db

@features_1270_p
It looks like the development of this database has stopped. The last release was February 2006.

@features_1271_h3
McKoi

@features_1272_p
It looks like the development of this database has stopped. The last release was August 2004

@features_1273_h2
H2 in Use

@features_1274_p
For a list of applications that work with or use H2, see: <a href="links.html">Links</a> .

@features_1275_h2
Connection Modes

@features_1276_p
The following connection modes are supported:

@features_1277_li
Embedded mode (local connections using JDBC)

@features_1278_li
Server mode (remote connections using JDBC or ODBC over TCP/IP)

@features_1279_li
Mixed mode (local and remote connections at the same time)

@features_1280_h3
Embedded Mode

@features_1281_p
In embedded mode, an application opens a database from within the same JVM using JDBC. This is the fastest and easiest connection mode. The disadvantage is that a database may only be open in one virtual machine (and class loader) at any time. As in all modes, both persistent and in-memory databases are supported. There is no limit on the number of database open concurrently, or on the number of open connections.

@features_1282_h3
Server Mode

@features_1283_p
When using the server mode (sometimes called remote mode or client/server mode), an application opens a database remotely using the JDBC or ODBC API. A server needs to be started within the same or another virtual machine, or on another computer. Many applications can connect to the same database at the same time. The server mode is slower than the embedded mode, because all data is transferred over TCP/IP. As in all modes, both persistent and in-memory databases are supported. There is no limit on the number of database open concurrently, or on the number of open connections.

@features_1284_h3
Mixed Mode

@features_1285_p
The mixed mode is a combination of the embedded and the server mode. The first application that connects to a database does that in embedded mode, but also starts a server so that other applications (running in different processes or virtual machines) can concurrently access the same data. The local connections are as fast as if the database is used in just the embedded mode, while the remote connections are a bit slower.

@features_1286_p
The server can be started and stopped from within the application (using the server API), or automatically (automatic mixed mode). When using the <a href="#auto_mixed_mode">automatic mixed mode</a> , all clients that want to connect to the database (no matter if it's an local or remote connection) can do so using the exact same database URL.

@features_1287_h2
Database URL Overview

@features_1288_p
This database supports multiple connection modes and connection settings. This is achieved using different database URLs. Settings in the URLs are not case sensitive.

@features_1289_th
Topic

@features_1290_th
URL Format and Examples

@features_1291_a
Embedded (local) connection

@features_1292_td
jdbc:h2:[file:][&lt;path&gt;]&lt;databaseName&gt;

@features_1293_td
jdbc:h2:~/test

@features_1294_td
jdbc:h2:file:/data/sample

@features_1295_td
jdbc:h2:file:C:/data/sample (Windows only)

@features_1296_a
In-memory (private)

@features_1297_td
jdbc:h2:mem:

@features_1298_a
In-memory (named)

@features_1299_td
jdbc:h2:mem:&lt;databaseName&gt;

@features_1300_td
jdbc:h2:mem:test_mem

@features_1301_a
Server mode (remote connections)

@features_1302_a
using TCP/IP

@features_1303_td
jdbc:h2:tcp://&lt;server&gt;[:&lt;port&gt;]/[&lt;path&gt;]&lt;databaseName&gt;

@features_1304_td
jdbc:h2:tcp://localhost/~/test

@features_1305_td
jdbc:h2:tcp://dbserv:8084/~/sample

@features_1306_a
Server mode (remote connections)

@features_1307_a
using SSL/TLS

@features_1308_td
jdbc:h2:ssl://&lt;server&gt;[:&lt;port&gt;]/&lt;databaseName&gt;

@features_1309_td
jdbc:h2:ssl://secureserv:8085/~/sample;

@features_1310_a
Using encrypted files

@features_1311_td
jdbc:h2:&lt;url&gt;;CIPHER=[AES|XTEA]

@features_1312_td
jdbc:h2:ssl://secureserv/~/testdb;CIPHER=AES

@features_1313_td
jdbc:h2:file:~/secure;CIPHER=XTEA

@features_1314_a
File locking methods

@features_1315_td
jdbc:h2:&lt;url&gt;;FILE_LOCK={NO|FILE|SOCKET}

@features_1316_td
jdbc:h2:file:~/quickAndDirty;FILE_LOCK=NO

@features_1317_td
jdbc:h2:file:~/private;CIPHER=XTEA;FILE_LOCK=SOCKET

@features_1318_a
Only open if it already exists

@features_1319_td
jdbc:h2:&lt;url&gt;;IFEXISTS=TRUE

@features_1320_td
jdbc:h2:file:~/sample;IFEXISTS=TRUE

@features_1321_a
Don't close the database when the VM exits

@features_1322_td
jdbc:h2:&lt;url&gt;;DB_CLOSE_ON_EXIT=FALSE

@features_1323_a
User name and/or password

@features_1324_td
jdbc:h2:&lt;url&gt;[;USER=&lt;username&gt;][;PASSWORD=&lt;value&gt;]

@features_1325_td
jdbc:h2:file:~/sample;USER=sa;PASSWORD=123

@features_1326_a
Log index changes

@features_1327_td
jdbc:h2:&lt;url&gt;;LOG=2

@features_1328_td
jdbc:h2:file:~/sample;LOG=2

@features_1329_a
Debug trace settings

@features_1330_td
jdbc:h2:&lt;url&gt;;TRACE_LEVEL_FILE=&lt;level 0..3&gt;

@features_1331_td
jdbc:h2:file:~/sample;TRACE_LEVEL_FILE=3

@features_1332_a
Ignore unknown settings

@features_1333_td
jdbc:h2:&lt;url&gt;;IGNORE_UNKNOWN_SETTINGS=TRUE

@features_1334_a
Custom file access mode

@features_1335_td
jdbc:h2:&lt;url&gt;;ACCESS_MODE_LOG=rws;ACCESS_MODE_DATA=rws

@features_1336_a
Database in a zip file

@features_1337_td
jdbc:h2:zip:&lt;zipFileName&gt;!/&lt;databaseName&gt;

@features_1338_td
jdbc:h2:zip:~/db.zip!/test

@features_1339_a
Compatibility mode

@features_1340_td
jdbc:h2:&lt;url&gt;;MODE=&lt;databaseType&gt;

@features_1341_td
jdbc:h2:~/test;MODE=MYSQL

@features_1342_a
Auto-reconnect

@features_1343_td
jdbc:h2:&lt;url&gt;;AUTO_RECONNECT=TRUE

@features_1344_td
jdbc:h2:tcp://localhost/~/test;AUTO_RECONNECT=TRUE

@features_1345_a
Automatic mixed mode

@features_1346_td
jdbc:h2:&lt;url&gt;;AUTO_SERVER=TRUE

@features_1347_td
jdbc:h2:~/test;AUTO_SERVER=TRUE

@features_1348_a
Changing other settings

@features_1349_td
jdbc:h2:&lt;url&gt;;&lt;setting&gt;=&lt;value&gt;[;&lt;setting&gt;=&lt;value&gt;...]

@features_1350_td
jdbc:h2:file:~/sample;TRACE_LEVEL_SYSTEM_OUT=3

@features_1351_h2
Connecting to an Embedded (Local) Database

@features_1352_p
The database URL for connecting to a local database is <code>jdbc:h2:[file:][&lt;path&gt;]&lt;databaseName&gt;</code> . The prefix <code>file:</code> is optional. If no or only a relative path is used, then the current working directory is used as a starting point. The case sensitivity of the path and database name depend on the operating system, however it is recommended to use lowercase letters only. The database name must be at least three characters long (a limitation of File.createTempFile). To point to the user home directory, use ~/, as in: jdbc:h2:~/test.

@features_1353_h2
Memory-Only Databases

@features_1354_p
For certain use cases (for example: rapid prototyping, testing, high performance operations, read-only databases), it may not be required to persist data, or persist changes to the data. This database supports the memory-only mode, where the data is not persisted.

@features_1355_p
In some cases, only one connection to a memory-only database is required. This means the database to be opened is private. In this case, the database URL is <code>jdbc:h2:mem:</code> Opening two connections within the same virtual machine means opening two different (private) databases.

@features_1356_p
Sometimes multiple connections to the same memory-only database are required. In this case, the database URL must include a name. Example: <code>jdbc:h2:mem:db1</code> . Accessing the same database in this way only works within the same virtual machine and class loader environment.

@features_1357_p
It is also possible to access a memory-only database remotely (or from multiple processes in the same machine) using TCP/IP or SSL/TLS. An example database URL is: <code>jdbc:h2:tcp://localhost/mem:db1</code> .

@features_1358_p
By default, closing the last connection to a database closes the database. For an in-memory database, this means the content is lost. To keep the database open, add ;DB_CLOSE_DELAY=-1 to the database URL. To keep the content of an in-memory database as long as the virtual machine is alive, use <code>jdbc:h2:mem:test;DB_CLOSE_DELAY=-1</code> .

@features_1359_h2
Database Files Encryption

@features_1360_p
The database files can be encrypted. Two encryption algorithms are supported: AES and XTEA. To use file encryption, you need to specify the encryption algorithm (the 'cipher') and the file password (in addition to the user password) when connecting to the database.

@features_1361_h3
Creating a New Database with File Encryption

@features_1362_p
By default, a new database is automatically created if it does not exist yet. To create an encrypted database, connect to it as it would already exist.

@features_1363_h3
Connecting to an Encrypted Database

@features_1364_p
The encryption algorithm is set in the database URL, and the file password is specified in the password field, before the user password. A single space separates the file password and the user password; the file password itself may not contain spaces. File passwords and user passwords are case sensitive. Here is an example to connect to a password-encrypted database:

@features_1365_h3
Encrypting or Decrypting a Database

@features_1366_p
To encrypt an existing database, use the ChangeFileEncryption tool. This tool can also decrypt an encrypted database, or change the file encryption key. The tool is available from within the H2 Console in the Tools section, or you can run it from the command line. The following command line will encrypt the database 'test' in the user home directory with the file password 'filepwd' and the encryption algorithm AES:

@features_1367_h2
Database File Locking

@features_1368_p
Whenever a database is opened, a lock file is created to signal other processes that the database is in use. If database is closed, or if the process that opened the database terminates, this lock file is deleted.

@features_1369_p
The following file locking methods are implemented:

@features_1370_li
The default method is 'file' and uses a watchdog thread to protect the database file. The watchdog reads the lock file each second.

@features_1371_li
The second method is 'socket' and opens a server socket. The socket method does not require reading the lock file every second. The socket method should only be used if the database files are only accessed by one (and always the same) computer.

@features_1372_li
It is also possible to open the database without file locking; in this case it is up to the application to protect the database files.

@features_1373_p
To open the database with a different file locking method, use the parameter 'FILE_LOCK'. The following code opens the database with the 'socket' locking method:

@features_1374_p
The following code forces the database to not create a lock file at all. Please note that this is unsafe as another process is able to open the same database, possibly leading to data corruption:

@features_1375_p
For more information about the algorithms, see <a href="advanced.html#file_locking_protocols">Advanced / File Locking Protocols</a> .

@features_1376_h2
Opening a Database Only if it Already Exists

@features_1377_p
By default, when an application calls <code>DriverManager.getConnection(url, ...)</code> and the database specified in the URL does not yet exist, a new (empty) database is created. In some situations, it is better to restrict creating new databases, and only allow to open existing databases. To do this, add <code>;ifexists=true</code> to the database URL. In this case, if the database does not already exist, an exception is thrown when trying to connect. The connection only succeeds when the database already exists. The complete URL may look like this:

@features_1378_h2
Closing a Database

@features_1379_h3
Delayed Database Closing

@features_1380_p
Usually, a database is closed when the last connection to it is closed. In some situations this slows down the application, for example when it is not possible to keep at least one connection open. The automatic closing of a database can be delayed or disabled with the SQL statement SET DB_CLOSE_DELAY &lt;seconds&gt;. The parameter &lt;seconds&gt; specifies the number of seconds to keep a database open after the last connection to it was closed. The following statement will keep a database open for 10 seconds after the last connection was closed:

@features_1381_p
The value -1 means the database is not closed automatically. The value 0 is the default and means the database is closed when the last connection is closed. This setting is persistent and can be set by an administrator only. It is possible to set the value in the database URL: <code>jdbc:h2:~/test;DB_CLOSE_DELAY=10</code> .

@features_1382_h3
Don't Close a Database when the VM Exits

@features_1383_p
By default, a database is closed when the last connection is closed. However, if it is never closed, the database is closed when the virtual machine exits normally, using a shutdown hook. In some situations, the database should not be closed in this case, for example because the database is still used at virtual machine shutdown (to store the shutdown process in the database for example). For those cases, the automatic closing of the database can be disabled in the database URL. The first connection (the one that is opening the database) needs to set the option in the database URL (it is not possible to change the setting afterwards). The database URL to disable database closing on exit is:

@features_1384_h2
Log Index Changes

@features_1385_p
Usually, changes to the index file are not logged for performance. If the index file is corrupt or missing when opening a database, it is re-created from the data. The index file can get corrupt when the database is not shut down correctly, because of power failure or abnormal program termination. In some situations, for example when using very large databases (over a few hundred MB), re-creating the index file takes very long. In these situations it may be better to log changes to the index file, so that recovery from a corrupted index file is fast. To enable log index changes, add LOG=2 to the URL, as in <code>jdbc:h2:~/test;LOG=2</code> . This setting should be specified when connecting. The update performance of the database will be reduced when using this option.

@features_1386_h2
Ignore Unknown Settings

@features_1387_p
Some applications (for example OpenOffice.org Base) pass some additional parameters when connecting to the database. Why those parameters are passed is unknown. The parameters PREFERDOSLIKELINEENDS and IGNOREDRIVERPRIVILEGES are such examples; they are simply ignored to improve the compatibility with OpenOffice.org. If an application passes other parameters when connecting to the database, usually the database throws an exception saying the parameter is not supported. It is possible to ignored such parameters by adding ;IGNORE_UNKNOWN_SETTINGS=TRUE to the database URL.

@features_1388_h2
Changing Other Settings when Opening a Connection

@features_1389_p
In addition to the settings already described, other database settings can be passed in the database URL. Adding <code>;setting=value</code> at the end of a database URL is the same as executing the statement <code>SET setting value</code> just after connecting. For a list of supported settings, see <a href="grammar.html">SQL Grammar</a> .

@features_1390_h2
Custom File Access Mode

@features_1391_p
Usually, the database opens log, data and index files with the access mode 'rw', meaning read-write (except for read only databases, where the mode 'r' is used). To open a database in read-only mode if the files are not read-only, use ACCESS_MODE_DATA=r. Also supported are 'rws' and 'rwd'. The access mode used for log files is set via ACCESS_MODE_LOG; for data and index files use ACCESS_MODE_DATA. These settings must be specified in the database URL:

@features_1392_p
For more information see <a href="advanced.html#durability_problems">Durability Problems</a> . On many operating systems the access mode 'rws' does not guarantee that the data is written to the disk.

@features_1393_h2
Multiple Connections

@features_1394_h3
Opening Multiple Databases at the Same Time

@features_1395_p
An application can open multiple databases at the same time, including multiple connections to the same database. The number of open database is only limited by the memory available.

@features_1396_h3
Multiple Connections to the Same Database: Client/Server

@features_1397_p
If you want to access the same database at the same time from different processes or computers, you need to use the client / server mode. In this case, one process acts as the server, and the other processes (that could reside on other computers as well) connect to the server via TCP/IP (or SSL/TLS over TCP/IP for improved security).

@features_1398_h3
Multithreading Support

@features_1399_p
This database is multithreading-safe. That means, if an application is multi-threaded, it does not need to worry about synchronizing access to the database. Internally, most requests to the same database are synchronized. That means an application can use multiple threads that access the same database at the same time, however if one thread executes a long running query, the other threads need to wait.

@features_1400_h3
Locking, Lock-Timeout, Deadlocks

@features_1401_p
The database uses table level locks to give each connection a consistent state of the data. There are two kinds of locks: read locks (shared locks) and write locks (exclusive locks). All locks are released when the transaction commits or rolls back. When using the default transaction isolation level 'read committed', read locks are already released after each statement.

@features_1402_p
If a connection wants to reads from a table, and there is no write lock on the table, then a read lock is added to the table. If there is a write lock, then this connection waits for the other connection to release the lock. If a connection cannot get a lock for a specified time, then a lock timeout exception is thrown.

@features_1403_p
Usually, SELECT statements will generate read locks. This includes subqueries. Statements that modify data use write locks. It is also possible to lock a table exclusively without modifying data, using the statement SELECT ... FOR UPDATE. The statements COMMIT and ROLLBACK releases all open locks. The commands SAVEPOINT and ROLLBACK TO SAVEPOINT don't affect locks. The locks are also released when the autocommit mode changes, and for connections with autocommit set to true (this is the default), locks are released after each statement. The following statements generate locks:

@features_1404_th
Type of Lock

@features_1405_th
SQL Statement

@features_1406_td
Read

@features_1407_td
SELECT * FROM TEST;

@features_1408_td
CALL SELECT MAX(ID) FROM TEST;

@features_1409_td
SCRIPT;

@features_1410_td
Write

@features_1411_td
SELECT * FROM TEST WHERE 1=0 FOR UPDATE;

@features_1412_td
Write

@features_1413_td
INSERT INTO TEST VALUES(1, 'Hello');

@features_1414_td
INSERT INTO TEST SELECT * FROM TEST;

@features_1415_td
UPDATE TEST SET NAME='Hi';

@features_1416_td
DELETE FROM TEST;

@features_1417_td
Write

@features_1418_td
ALTER TABLE TEST ...;

@features_1419_td
CREATE INDEX ... ON TEST ...;

@features_1420_td
DROP INDEX ...;

@features_1421_p
The number of seconds until a lock timeout exception is thrown can be set separately for each connection using the SQL command SET LOCK_TIMEOUT &lt;milliseconds&gt;. The initial lock timeout (that is the timeout used for new connections) can be set using the SQL command SET DEFAULT_LOCK_TIMEOUT &lt;milliseconds&gt;. The default lock timeout is persistent.

@features_1422_h2
Database File Layout

@features_1423_p
There are a number of files created for persistent databases. Unlike some other databases, not every table and/or index is stored in its own file. Instead, usually only the following files are created: A data file, an index file, a log file, and a database lock file (exists only while the database is in use). In addition to that, a file is created for each large object (CLOB/BLOB) larger than a certain size, and temporary files for large result sets. If the database trace option is enabled, trace files are created. The following files can be created by the database:

@features_1424_th
File Name

@features_1425_th
Description

@features_1426_th
Number of Files

@features_1427_td
test.data.db

@features_1428_td
Data file.

@features_1429_td
Contains the data for all tables.

@features_1430_td
Format: &lt;database&gt;.data.db

@features_1431_td
1 per database

@features_1432_td
test.index.db

@features_1433_td
Index file.

@features_1434_td
Contains the data for all (b tree) indexes.

@features_1435_td
Format: &lt;database&gt;.index.db

@features_1436_td
1 per database

@features_1437_td
test.0.log.db

@features_1438_td
Transaction log file.

@features_1439_td
The transaction log is used for recovery.

@features_1440_td
Format: &lt;database&gt;.&lt;id&gt;.log.db

@features_1441_td
0 or more per database

@features_1442_td
test.lock.db

@features_1443_td
Database lock file.

@features_1444_td
Exists only while the database is open.

@features_1445_td
Format: &lt;database&gt;.lock.db

@features_1446_td
1 per database

@features_1447_td
test.trace.db

@features_1448_td
Trace file.

@features_1449_td
Contains trace information.

@features_1450_td
Format: &lt;database&gt;.trace.db

@features_1451_td
If the file is too big, it is renamed to &lt;database&gt;.trace.db.old

@features_1452_td
1 per database

@features_1453_td
test.lobs.db/1.t15.lob.db

@features_1454_td
Large object.

@features_1455_td
Contains the data for BLOB or CLOB values.

@features_1456_td
Format: &lt;id&gt;.t&lt;tableId&gt;.lob.db

@features_1457_td
1 per value

@features_1458_td
test.123.temp.db

@features_1459_td
Temporary file.

@features_1460_td
Contains a temporary blob or a large result set.

@features_1461_td
Format: &lt;database&gt;.&lt;id&gt;.temp.db

@features_1462_td
1 per object

@features_1463_h3
Moving and Renaming Database Files

@features_1464_p
Database name and location are not stored inside the database files.

@features_1465_p
While a database is closed, the files can be moved to another directory, and they can be renamed as well (as long as all files start with the same name).

@features_1466_p
As there is no platform specific data in the files, they can be moved to other operating systems without problems.

@features_1467_h3
Backup

@features_1468_p
When the database is closed, it is possible to backup the database files. Please note that index files do not need to be backed up, because they contain redundant data, and will be recreated automatically if they don't exist.

@features_1469_p
To backup data while the database is running, the SQL command SCRIPT can be used.

@features_1470_h2
Logging and Recovery

@features_1471_p
Whenever data is modified in the database and those changes are committed, the changes are logged to disk (except for in-memory objects). The changes to the data file itself are usually written later on, to optimize disk access. If there is a power failure, the data and index files are not up-to-date. But because the changes are in the log file, the next time the database is opened, the changes that are in the log file are re-applied automatically.

@features_1472_p
Please note that index file updates are not logged by default. If the database is opened and recovery is required, the index file is rebuilt from scratch.

@features_1473_p
There is usually only one log file per database. This file grows until the database is closed successfully, and is then deleted. Or, if the file gets too big, the database switches to another log file (with a higher id). It is possible to force the log switching by using the CHECKPOINT command.

@features_1474_p
If the database file is corrupted, because the checksum of a record does not match (for example, if the file was edited with another application), the database can be opened in recovery mode. In this case, errors in the database are logged but not thrown. The database should be backed up to a script and re-built as soon as possible. To open the database in the recovery mode, use a database URL must contain RECOVER=1, as in jdbc:h2:~/test;RECOVER=1. Indexes are rebuilt in this case, and the summary (object allocation table) is not read in this case, so opening the database takes longer.

@features_1475_h2
Compatibility

@features_1476_p
All database engines behave a little bit different. Where possible, H2 supports the ANSI SQL standard, and tries to be compatible to other databases. There are still a few differences however:

@features_1477_p
In MySQL text columns are case insensitive by default, while in H2 they are case sensitive. However H2 supports case insensitive columns as well. To create the tables with case insensitive texts, append IGNORECASE=TRUE to the database URL (example: <code>jdbc:h2:~/test;IGNORECASE=TRUE</code> ).

@features_1478_h3
Compatibility Modes

@features_1479_p
For certain features, this database can emulate the behavior of specific databases. Not all features or differences of those databases are implemented. Here is the list of currently supported modes and the differences to the regular mode:

@features_1480_h3
DB2 Compatibility Mode

@features_1481_p
To use the IBM DB2 mode, use the database URL <code>jdbc:h2:~/test;MODE=DB2</code> or the SQL statement <code>SET MODE DB2</code> .

@features_1482_li
For aliased columns, ResultSetMetaData.getColumnName() returns the alias name  and getTableName() returns null.

@features_1483_li
Support for the syntax [OFFSET .. ROW] [FETCH ... ONLY]  as an alternative for LIMIT .. OFFSET.

@features_1484_h3
Derby Compatibility Mode

@features_1485_p
To use the Apache Derby mode, use the database URL <code>jdbc:h2:~/test;MODE=Derby</code> or the SQL statement <code>SET MODE Derby</code> .

@features_1486_li
For aliased columns, ResultSetMetaData.getColumnName() returns the alias name  and getTableName() returns null.

@features_1487_li
For unique indexes, NULL is distinct. That means only one row with NULL  in one of the columns is allowed.

@features_1488_h3
HSQLDB Compatibility Mode

@features_1489_p
To use the HSQLDB mode, use the database URL <code>jdbc:h2:~/test;MODE=HSQLDB</code> or the SQL statement <code>SET MODE HSQLDB</code> .

@features_1490_li
For aliased columns, ResultSetMetaData.getColumnName() returns the alias name  and getTableName() returns null.

@features_1491_li
When converting the scale of decimal data, the number is only converted if the new scale is  smaller than the current scale. Usually, the scale is converted and 0s are added if required.

@features_1492_li
Concatenation with NULL results in NULL. Usually, NULL is treated as an empty  string if only one of the operands is NULL, and NULL is only returned if both operands are NULL.

@features_1493_li
For unique indexes, NULL is distinct. That means only one row with NULL  in one of the columns is allowed.

@features_1494_h3
MS SQL Server Compatibility Mode

@features_1495_p
To use the MS SQL Server mode, use the database URL <code>jdbc:h2:~/test;MODE=MSSQLServer</code> or the SQL statement <code>SET MODE MSSQLServer</code> .

@features_1496_li
For aliased columns, ResultSetMetaData.getColumnName() returns the alias name  and getTableName() returns null.

@features_1497_li
Identifiers may be quoted using square brackets as in [Test].

@features_1498_li
For unique indexes, NULL is distinct. That means only one row with NULL  in one of the columns is allowed.

@features_1499_h3
MySQL Compatibility Mode

@features_1500_p
To use the MySQL mode, use the database URL <code>jdbc:h2:~/test;MODE=MySQL</code> or the SQL statement <code>SET MODE MySQL</code> .

@features_1501_li
When inserting data, if a column is defined to be NOT NULL and NULL is inserted,  then a 0 (or empty string, or the current timestamp for timestamp columns) value is used.  Usually, this operation is not allowed and an exception is thrown.

@features_1502_li
Creating indexes in the CREATE TABLE statement is allowed.

@features_1503_li
Meta data calls return identifiers in lower case.

@features_1504_li
When converting a floating point number to an integer, the fractional  digits are not truncated, but the value is rounded.

@features_1505_h3
Oracle Compatibility Mode

@features_1506_p
To use the Oracle mode, use the database URL <code>jdbc:h2:~/test;MODE=Oracle</code> or the SQL statement <code>SET MODE Oracle</code> .

@features_1507_li
For aliased columns, ResultSetMetaData.getColumnName() returns the alias name  and getTableName() returns null.

@features_1508_li
When using unique indexes, multiple rows with NULL in all columns  are allowed, however it is not allowed to have multiple rows with the  same values otherwise.

@features_1509_h3
PostgreSQL Compatibility Mode

@features_1510_p
To use the PostgreSQL mode, use the database URL <code>jdbc:h2:~/test;MODE=PostgreSQL</code> or the SQL statement <code>SET MODE PostgreSQL</code> .

@features_1511_li
For aliased columns, ResultSetMetaData.getColumnName() returns the alias name  and getTableName() returns null.

@features_1512_li
Concatenation with NULL results in NULL. Usually, NULL is treated as an empty  string if only one of the operands is NULL, and NULL is only returned if both operands are NULL.

@features_1513_li
When converting a floating point number to an integer, the fractional  digits are not be truncated, but the value is rounded.

@features_1514_li
The system columns 'CTID' and 'OID' are supported.

@features_1515_h2
Auto-Reconnect

@features_1516_p
The auto-reconnect feature causes the JDBC driver to reconnect to the database if the connection is lost. The automatic re-connect only occurs when auto-commit is enabled; if auto-commit is disabled, an exception is thrown.

@features_1517_p
Re-connecting will open a new session. After an automatic re-connect, variables and local temporary tables definitions (excluding data) are re-created. The contents of the system table INFORMATION_SCHEMA.SESSION_STATE contains all client side state that is re-created.

@features_1518_h2
Automatic Mixed Mode

@features_1519_p
Multiple processes can access the same database without having to start the server manually. To do that, append <code>;AUTO_SERVER=TRUE</code> to the database URL. You can use the same database URL no matter if the database is already open or not.

@features_1520_p
When using this mode, the first connection to the database is made in embedded mode, and additionally a server is started internally. If the database is already open in another process, the server mode is used automatically.

@features_1521_p
The application that opens the first connection to the database uses the embedded mode, which is faster than the server mode. Therefore the main application should open the database first if possible. The first connection automatically starts a server on a random port. This server allows remote connections, however only to this database (to ensure that, the client reads .lock.db file and sends the the random key that is stored there to the server). When the first connection is closed, the server stops. If other (remote) connections are still open, one of them will then start a server (auto-reconnect is enabled automatically).

@features_1522_p
This mode has three disadvantages: All processes need to have access to the database files. Then, if the first connection is closed (the connection that started the server), open transactions of other connections will be rolled back. Also, explicit client/server connections (using jdbc:h2:tcp:// or ssl://) are not supported.

@features_1523_p
Here is an example how to use this mode. Application 1 and 2 are not necessarily started on the same computer, but they need to have access to the database files. Application 1 and 2 are typically two different processes (however they could run within the same process).

@features_1524_h2
Using the Trace Options

@features_1525_p
To find problems in an application, it is sometimes good to see what database operations where executed. This database offers the following trace features:

@features_1526_li
Trace to System.out and/or a file

@features_1527_li
Support for trace levels OFF, ERROR, INFO, and DEBUG

@features_1528_li
The maximum size of the trace file can be set

@features_1529_li
It is possible to generate Java source code from the trace file

@features_1530_li
Trace can be enabled at runtime by manually creating a file

@features_1531_h3
Trace Options

@features_1532_p
The simplest way to enable the trace option is setting it in the database URL. There are two settings, one for System.out (TRACE_LEVEL_SYSTEM_OUT) tracing, and one for file tracing (TRACE_LEVEL_FILE). The trace levels are 0 for OFF, 1 for ERROR (the default), 2 for INFO and 3 for DEBUG. A database URL with both levels set to DEBUG is:

@features_1533_p
The trace level can be changed at runtime by executing the SQL command <code>SET TRACE_LEVEL_SYSTEM_OUT level</code> (for System.out tracing) or <code>SET TRACE_LEVEL_FILE level</code> (for file tracing). Example:

@features_1534_h3
Setting the Maximum Size of the Trace File

@features_1535_p
When using a high trace level, the trace file can get very big quickly. The default size limit is 16 MB, if the trace file exceeds this limit, it is renamed to .old and a new file is created. If another .old file exists, it is deleted. The size limit can be changed using the SQL statement <code>SET TRACE_MAX_FILE_SIZE maximumFileSizeInMB</code> . Example:

@features_1536_h3
Java Code Generation

@features_1537_p
When setting the trace level to INFO or DEBUG, Java source code is generated as well. This allows to reproduce problems more easily. The trace file looks like this:

@features_1538_p
To filter the Java source code, use the ConvertTraceFile tool as follows:

@features_1539_p
The generated file <code>Test.java</code> will contain the Java source code. The generated source code may be too large to compile (the size of a Java method is limited). If this is the case, the source code needs to be split in multiple methods. The password is not listed in the trace file and therefore not included in the source code.

@features_1540_h2
Using Other Logging APIs

@features_1541_p
By default, this database uses its own native 'trace' facility. This facility is called 'trace' and not 'log' within this database to avoid confusion with the transaction log. Trace messages can be written to both file and System.out. In most cases, this is sufficient, however sometimes it is better to use the same facility as the application, for example Log4j. To do that, this database support SLF4J.

@features_1542_a
SLF4J

@features_1543_p
is a simple facade for various logging APIs and allows to plug in the desired implementation at deployment time. SLF4J supports implementations such as Logback, Log4j, Jakarta Commons Logging (JCL), JDK 1.4 logging, x4juli, and Simple Log.

@features_1544_p
To enable SLF4J, set the file trace level to 4 in the database URL:

@features_1545_p
Changing the log mechanism is not possible after the database is open, that means executing the SQL statement SET TRACE_LEVEL_FILE 4 when the database is already open will not have the desired effect. To use SLF4J, all required jar files need to be in the classpath. If it does not work, check the file &lt;database&gt;.trace.db for error messages.

@features_1546_h2
Read Only Databases

@features_1547_p
If the database files are read-only, then the database is read-only as well. It is not possible to create new tables, add or modify data in this database. Only SELECT and CALL statements are allowed. To create a read-only database, close the database so that the log file gets smaller. Do not delete the log file. Then, make the database files read-only using the operating system. When you open the database now, it is read-only. There are two ways an application can find out whether database is read-only: By calling Connection.isReadOnly() or by executing the SQL statement CALL READONLY().

@features_1548_h2
Read Only Databases in Zip or Jar File

@features_1549_p
To create a read-only database in a zip file, first create a regular persistent database, and then create a backup. If you are using a database named 'test', an easy way to do that is using the Backup tool or the BACKUP SQL statement:

@features_1550_p
The database must not have pending changes, that means you need to close all connections to the database, open one single connection, and then execute the statement. Afterwards, you can log out, and directly open the database in the zip file using the following database URL:

@features_1551_p
Databases in zip files are read-only. The performance for some queries will be slower than when using a regular database, because random access in zip files is not supported (only streaming). How much this affects the performance depends on the queries and the data. The database is not read in memory; therefore large databases are supported as well. The same indexes are used as when using a regular database.

@features_1552_h2
Graceful Handling of Low Disk Space Situations

@features_1553_p
If the database needs more disk space, it calls the database event listener if one is installed. The application may then delete temporary files, or display a message and wait until the user has resolved the problem. To install a listener, run the SQL statement SET DATABASE_EVENT_LISTENER or use a database URL of the form jdbc:h2:~/test;DATABASE_EVENT_LISTENER='com.acme.DbListener' (the quotes around the class name are required). See also the DatabaseEventListener API.

@features_1554_h3
Opening a Corrupted Database

@features_1555_p
If a database cannot be opened because the boot info (the SQL script that is run at startup) is corrupted, then the database can be opened by specifying a database event listener. The exceptions are logged, but opening the database will continue.

@features_1556_h2
Computed Columns / Function Based Index

@features_1557_p
Function indexes are not directly supported by this database, but they can be emulated by using computed columns. For example, if an index on the upper-case version of a column is required, create a computed column with the upper-case version of the original column, and create an index for this column:

@features_1558_p
When inserting data, it is not required (and not allowed) to specify a value for the upper-case version of the column, because the value is generated. But you can use the column when querying the table:

@features_1559_h2
Multi-Dimensional Indexes

@features_1560_p
A tool is provided to execute efficient multi-dimension (spatial) range queries. This database does not support a specialized spatial index (R-Tree or similar). Instead, the B-Tree index is used. For each record, the multi-dimensional key is converted (mapped) to a single dimensional (scalar) value. This value specifies the location on a space-filling curve.

@features_1561_p
Currently, Z-order (also called N-order or Morton-order) is used; Hilbert curve could also be used, but the implementation is more complex. The algorithm to convert the multi-dimensional value is called bit-interleaving. The scalar value is indexed using a B-Tree index (usually using a computed column).

@features_1562_p
The method can result in a drastic performance improvement over just using an index on the first column. Depending on the data and number of dimensions, the improvement is usually higher than factor 5. The tool generates a SQL query from a specified multi-dimensional range. The method used is not database dependent, and the tool can easily be ported to other databases. For an example how to use the tool, please have a look at the sample code provided in TestMultiDimension.java.

@features_1563_h2
Using Passwords

@features_1564_h3
Using Secure Passwords

@features_1565_p
Remember that weak passwords can be broken no matter of the encryption and security protocol. Don't use passwords that can be found in a dictionary. Also appending numbers does not make them secure. A way to create good passwords that can be remembered is, take the first letters of a sentence, use upper and lower case characters, and creatively include special characters. Example:

@features_1566_p
i'sE2rtPiUKtT (it's easy to remember this password if you know the trick)

@features_1567_h3
Passwords: Using Char Arrays instead of Strings

@features_1568_p
Java Strings are immutable objects and cannot be safely 'destroyed' by the application. After creating a String, it will remain in the main memory of the computer at least until it is garbage collected. The garbage collection cannot be controlled by the application, and even if it is garbage collected the data may still remain in memory. It might also be possible that the part of memory containing the password is swapped to disk (because not enough main memory is available).

@features_1569_p
An attacker might have access to the swap file of the operating system. It is therefore a good idea to use char arrays instead of Strings to store passwords. Char arrays can be cleared (filled with zeros) after use, and therefore the password will not be stored in the swap file.

@features_1570_p
This database supports using char arrays instead of String to pass user and file passwords. The following code can be used to do that:

@features_1571_p
This example requires Java 1.6. When using Swing, use javax.swing.JPasswordField.

@features_1572_h3
Passing the User Name and/or Password in the URL

@features_1573_p
Instead of passing the user name as a separate parameter as in <code>Connection conn = DriverManager.  getConnection("jdbc:h2:~/test", "sa", "123");</code> the user name (and/or password) can be supplied in the URL itself: <code>Connection conn = DriverManager.  getConnection("jdbc:h2:~/test;USER=sa;PASSWORD=123");</code> The settings in the URL override the settings passed as a separate parameter.

@features_1574_h2
User-Defined Functions and Stored Procedures

@features_1575_p
In addition to the built-in functions, this database supports user-defined Java functions. In this database, Java functions can be used as stored procedures as well. A function must be declared (registered) before it can be used. Only static Java methods are supported; both the class and the method must be public. Example Java method:

@features_1576_p
The Java function must be registered in the database by calling CREATE ALIAS:

@features_1577_p
For a complete sample application, see src/test/org/h2/samples/Function.java.

@features_1578_h3
Function Data Type Mapping

@features_1579_p
Functions that accept non-nullable parameters such as 'int' will not be called if one of those parameters is NULL. Instead, the result of the function is NULL. If the function should be called if a parameter is NULL, you need to use 'java.lang.Integer' instead of 'int'.

@features_1580_h3
Functions that require a Connection

@features_1581_p
If the first parameter of a Java function is a java.sql.Connection, then the connection to database is provided. This connection does not need to be closed before returning. When calling the method from within the SQL statement, this connection parameter does not need to be (can not be) specified.

@features_1582_h3
Functions throwing an Exception

@features_1583_p
If a function throws an Exception, then the current statement is rolled back and the exception is thrown to the application.

@features_1584_h3
Functions returning a Result Set

@features_1585_p
Functions may returns a result set. Such a function can be called with the CALL statement:

@features_1586_h3
Using SimpleResultSet

@features_1587_p
A function can create a result set using the SimpleResultSet tool:

@features_1588_h3
Using a Function as a Table

@features_1589_p
A function that returns a result set can be used like a table. However, in this case the function is called at least twice: First while parsing the statement to collect the column names (with parameters set to null where not known at compile time). And then, while executing the statement to get the data (maybe multiple times if this is a join). If the function is called just to get the column list, the URL of the connection passed to the function is <code>jdbc:columnlist:connection</code> . Otherwise, the URL of the connection is <code>jdbc:default:connection</code> .

@features_1590_h2
Triggers

@features_1591_p
This database supports Java triggers that are called before or after a row is updated, inserted or deleted. Triggers can be used for complex consistency checks, or to update related data in the database. It is also possible to use triggers to simulate materialized views. For a complete sample application, see src/test/org/h2/samples/TriggerSample.java. A Java trigger must implement the interface org.h2.api.Trigger:

@features_1592_p
The connection can be used to query or update data in other tables. The trigger then needs to be defined in the database:

@features_1593_p
The trigger can be used to veto a change, by throwing a SQLException.

@features_1594_h2
Compacting a Database

@features_1595_p
Empty space in the database file is re-used automatically. To re-build the indexes, the simplest way is to delete the .index.db file while the database is closed. However in some situations (for example after deleting a lot of data in a database), one sometimes wants to shrink the size of the database (compact a database). Here is a sample function to do this:

@features_1596_p
See also the sample application org.h2.samples.Compact. The commands SCRIPT / RUNSCRIPT can be used as well to create a backup of a database and re-build the database from the script.

@features_1597_h2
Cache Settings

@features_1598_p
The database keeps most frequently used data and index pages in the main memory. The amount of memory used for caching can be changed using the setting CACHE_SIZE. This setting can be set in the database connection URL (jdbc:h2:~/test;CACHE_SIZE=131072), or it can be changed at runtime using SET CACHE_SIZE size.

@features_1599_p
This database supports two cache page replacement algorithms: LRU (the default) and TQ. For LRU, the pages that were least frequently used are removed from the cache if it becomes full. The TQ (Two Queue, also called 2Q) algorithm is a bit more complicated: basically two queues are used. It is more resistant to table scans, however the overhead is a bit higher compared to the LRU. To use the cache algorithm TQ, use a database URL of the form jdbc:h2:~/test;CACHE_TYPE=TQ. The cache algorithm cannot be changed once the database is open.

@features_1600_p
Also supported is a second level soft reference cache. Rows in this cache are only garbage collected on low memory. By default the second level cache is disabled. To enable it, use the prefix SOFT_. Example: jdbc:h2:~/test;CACHE_TYPE=SOFT_LRU .

@features_1601_p
To get information about page reads and writes, and the current caching algorithm in use, call SELECT * FROM INFORMATION_SCHEMA.SETTINGS. The number of pages read / written is listed for the data and index file.

@fragments_1000_b
Search:

@fragments_1001_td
Highlight keyword(s)

@fragments_1002_a
Home

@fragments_1003_a
Quickstart

@fragments_1004_a
Installation

@fragments_1005_a
Tutorial

@fragments_1006_a
Features

@fragments_1007_a
Performance

@fragments_1008_a
Advanced Topics

@fragments_1009_a
JaQu

@fragments_1010_a
Download

@fragments_1011_b
Reference

@fragments_1012_a
SQL Grammar

@fragments_1013_a
Functions

@fragments_1014_a
Data Types

@fragments_1015_a
Javadoc

@fragments_1016_a
Docs as PDF (1 MB)

@fragments_1017_a
Error Analyzer

@fragments_1018_b
Appendix

@fragments_1019_a
Build

@fragments_1020_a
History &amp; Roadmap

@fragments_1021_a
Links

@fragments_1022_a
FAQ

@fragments_1023_a
License

@fragments_1024_td
&nbsp;

@frame_1000_h1
H2 Database Engine

@frame_1001_p
Welcome to H2, the free SQL database. The main feature of H2 are:

@frame_1002_li
It is free to use for everybody, source code is included

@frame_1003_li
Written in Java, but also available as native executable

@frame_1004_li
JDBC and (partial) ODBC API

@frame_1005_li
Embedded and client/server modes

@frame_1006_li
Clustering is supported

@frame_1007_li
A web client is included

@frame_1008_h2
No Javascript

@frame_1009_p
If you are not automatically redirected to the main page, then Javascript is currently disabled or your browser does not support Javascript. Some features (for example the integrated search) require Javascript.

@frame_1010_p
Please enable Javascript, or go ahead without it: <a href="main.html" style="font-size: 16px; font-weight: bold">H2 Database Engine</a>

@history_1000_h1
History and Roadmap

@history_1001_a
Change Log

@history_1002_a
Roadmap

@history_1003_a
History of this Database Engine

@history_1004_a
Why Java

@history_1005_a
Supporters

@history_1006_h2
Change Log

@history_1007_p
The up-to-date change log is available at <a href="http://www.h2database.com/html/changelog.html">http://www.h2database.com/html/changelog.html</a>

@history_1008_h2
Roadmap

@history_1009_p
The current roadmap is available at <a href="http://www.h2database.com/html/roadmap.html">http://www.h2database.com/html/roadmap.html</a>

@history_1010_h2
History of this Database Engine

@history_1011_p
The development of H2 was started in May 2004, but it was first published on December 14th 2005. The main author of H2, Thomas Mueller, is also the original developer of Hypersonic SQL. In 2001, he joined PointBase Inc. where he created PointBase Micro. At that point, he had to discontinue Hypersonic SQL, but then the HSQLDB Group was formed to continued to work on the Hypersonic SQL codebase. The name H2 stands for Hypersonic 2; however H2 does not share any code with Hypersonic SQL or HSQLDB. H2 is built from scratch.

@history_1012_h2
Why Java

@history_1013_p
A few reasons using a Java database are:

@history_1014_li
Very simple to integrate in Java applications

@history_1015_li
Support for many different platforms

@history_1016_li
More secure than native applications (no buffer overflows)

@history_1017_li
User defined functions (or triggers) run very fast

@history_1018_li
Unicode support

@history_1019_p
Some people think that Java is still too slow for low level operations, but this is not the case (not any more). In general, the code can be written a lot faster than using C or C++. Like that, it is possible to concentrate on improving the algorithms (that make the application faster) rather than porting the code and dealing with low level stuff (such as memory management or dealing with threads). Garbage collection is now probably faster than manual memory management.

@history_1020_p
A lot of features are already built in (for example Unicode, network libraries). It is very easy to write secure code because buffer overflows can not occur. Some features such as the reflection mechanism can be used for randomized testing.

@history_1021_p
Java is also future proof: A lot of companies support Java, and it is now open source.

@history_1022_p
This software does not rely on many Java libraries or other software, to increase the portability and ease of use, and for performance reasons. For example, the encryption algorithms and many library functions are implemented in the database instead of using the existing libraries. Libraries that are not available in open source Java implementations (such as Swing) are not used or only used for specific features.

@history_1023_h2
Supporters

@history_1024_p
Many thanks for those who helped by finding and reporting bugs, gave valuable feedback, spread the word and have translated this project. Also many thanks to the donors who contributed via PayPal:

@history_1025_a
SkyCash, Poland

@history_1026_li
Donald Bleyl, USA

@history_1027_li
lumber-mill.co.jp, Japan

@history_1028_li
Frank Berger, Germany

@history_1029_li
Ashwin Jayaprakash, USA

@history_1030_li
Florent Ramiere, France

@history_1031_li
Jun Iyama, Japan

@history_1032_li
Antonio Casqueiro, Portugal

@history_1033_li
Oliver Computing LLC, USA

@history_1034_li
Harpal Grover Consulting Inc., USA

@history_1035_li
Elisabetta Berlini, Italy

@history_1036_li
William Gilbert, USA

@history_1037_li
Antonio Dieguez, Chile

@history_1038_a
Ontology Works, USA

@history_1039_li
Pete Haidinyak, USA

@history_1040_li
William Osmond, USA

@history_1041_li
Joachim Ansorg, Germany

@history_1042_li
Oliver Soerensen, Germany

@installation_1000_h1
Installation

@installation_1001_a
Requirements

@installation_1002_a
Supported Platforms

@installation_1003_a
Installing the Software

@installation_1004_a
Directory Structure

@installation_1005_h2
Requirements

@installation_1006_p
To run the database, the following minimum software stack is known to work:

@installation_1007_li
Windows XP, Mac OS X, or Linux

@installation_1008_li
Recommended Windows file system: NTFS (FAT32 supports files up to 4 GB)

@installation_1009_li
Sun JDK 1.4 or newer

@installation_1010_li
Mozilla Firefox 1.5 or newer

@installation_1011_h2
Supported Platforms

@installation_1012_p
As this database is written in Java, it can run on many different platforms. It is tested with Java 1.4, 1.5, and 1.6 but can also be compiled to native code using GCJ. The source code does not use features of Java 1.5. Currently, the database is developed and tested on Windows XP and Mac OS X using the Sun JDK 1.5, but it also works in many other operating systems and using other Java runtime environments.

@installation_1013_h2
Installing the Software

@installation_1014_p
To install the software, run the installer or unzip it to a directory of your choice.

@installation_1015_h2
Directory Structure

@installation_1016_p
After installing, you should get the following directory structure:

@installation_1017_th
Directory

@installation_1018_th
Contents

@installation_1019_td
bin

@installation_1020_td
JAR and batch files

@installation_1021_td
docs

@installation_1022_td
Documentation

@installation_1023_td
docs/html

@installation_1024_td
HTML pages

@installation_1025_td
docs/javadoc

@installation_1026_td
Javadoc files

@installation_1027_td
ext

@installation_1028_td
External dependencies (downloaded when building)

@installation_1029_td
service

@installation_1030_td
Tools to run the database as a Windows Service

@installation_1031_td
src

@installation_1032_td
Source files

@jaqu_1000_h1
JaQu

@jaqu_1001_h2
What is JaQu

@jaqu_1002_p
JaQu stands for Java Query and allows to access databases using pure Java. JaQu provides a fluent interface (or internal DSL) for building SQL statements. JaQu replaces SQL, JDBC, and persistence frameworks such as Hibernate. JaQu is something like LINQ for Java (LINQ stands for "language integrated query" and is a Microsoft .NET technology). The following JaQu code:

@jaqu_1003_p
stands for the SQL statement:

@jaqu_1004_h2
Advantages and Differences to Other Data Access Tools

@jaqu_1005_p
Unlike SQL, JaQu can be easily integrated in Java applications. Because JaQu is pure Java, auto-complete in the IDE and Javadoc and are supported. Type checking is performed by the compiler. JaQu fully protects against SQL injection.

@jaqu_1006_p
JaQu is much smaller than persistence frameworks such as Hibernate. Unlike iBatis and Hibernate, no XML or annotation based configuration is required; instead the configuration (if required at all) is done in pure Java, in the application itself.

@jaqu_1007_p
JaQu does not require or contain any data caching mechanism. Like JDBC and iBatis, JaQu provides full control over when and what SQL statements are executed.

@jaqu_1008_h3
Restrictions

@jaqu_1009_p
Primitive types (eg. boolean, int, long, double) are not supported. Use Boolean, Integer, Long, and Double instead.

@jaqu_1010_h3
Why in Java?

@jaqu_1011_p
Most people use Java in their application. Mixing Java and another language (for example Scala or Groovy) in the same application is complicated: You would need to split the application and database code.

@jaqu_1012_h2
Current State

@jaqu_1013_p
JaQu is not yet stable, and not part of the h2 jar file. However the source code is included in H2, under:

@jaqu_1014_li
src/test/org/h2/test/jaqu/* (samples and tests)

@jaqu_1015_li
src/tools/org/h2/jaqu/* (framework)

@jaqu_1016_h2
Building the JaQu library

@jaqu_1017_p
To create the JaQu jar file, run: <code>build jarJaqu</code> . This will create the file <code>bin/h2jaqu.jar</code> .

@jaqu_1018_h2
Requirements

@jaqu_1019_p
JaQu requires Java 1.5. Annotations are not need. Currently, JaQu is only tested with the H2 database engine, however in theory it should work with any database that supports the JDBC API.

@jaqu_1020_h2
Example Code

@jaqu_1021_h2
Configuration

@jaqu_1022_p
JaQu does not require any configuration when using the default mapping. To define table indices, or if you want to map a class to a table with a different name, or a field to a column with another name, create a function called 'define' in the data class. Example:

@jaqu_1023_p
The method 'define()' contains the mapping definition. It is called once when the class is used for the first time. Like annotations, the mapping is defined in the class itself. Unlike when using annotations, the compiler can check the syntax even for multi-column objects (multi-column indexes, multi-column primary keys and so on). Because the definition is written in regular Java, the configuration can depend on the environment. This is not possible using annotations. Unlike XML mapping configuration, the configuration is integrated in the class itself.

@jaqu_1024_h2
Ideas

@jaqu_1025_p
This project has just been started, and nothing is fixed yet. Some ideas for what to implement are:

@jaqu_1026_li
Support queries on collections (instead of using a database).

@jaqu_1027_li
Provide API level compatibility with JPA (so that JaQu can be used as an extension of JPA).

@jaqu_1028_li
Internally use a JPA implementation (for example Hibernate) instead of SQL directly.

@jaqu_1029_li
Use PreparedStatements and cache them.

@jaqu_1030_h2
Related Projects

@jaqu_1031_a
Dreamsource ORM

@jaqu_1032_a
Empire-db

@jaqu_1033_a
JEQUEL: Java Embedded QUEry Language

@jaqu_1034_a
Joist

@jaqu_1035_a
JoSQL

@jaqu_1036_a
LIQUidFORM

@jaqu_1037_a
Quaere (Alias implementation)

@jaqu_1038_a
Quaere

@jaqu_1039_a
Querydsl

@jaqu_1040_a
Squill

@license_1000_h1
License

@license_1001_h2
Summary and License FAQ

@license_1002_p
H2 is dual licensed and available under a modified version of the MPL 1.1 ( <a href="http://www.mozilla.org/MPL">Mozilla Public License</a> ) or under the (unmodified) EPL 1.0 ( <a href="http://opensource.org/licenses/eclipse-1.0.php">Eclipse Public License</a> ). The changes to the MPL are

@license_1003_em
underlined</em> . There is a License FAQ for both the MPL and the EPL, most of that is applicable to the H2 License as well.

@license_1004_li
You can use H2 for free. You can integrate it into your application (including commercial applications),  and you can distribute it.

@license_1005_li
Files containing only your code are not covered by this license (it is 'commercial friendly').

@license_1006_li
Modifications to the H2 source code must be published.

@license_1007_li
You don't need to provide the source code of H2 if you did not modify anything.

@license_1008_p
However, nobody is allowed to rename H2, modify it a little, and sell it as a database engine without telling the customers it is in fact H2. This happened to HSQLDB: A company called 'bungisoft' copied HSQLDB, renamed it to 'RedBase', and tried to sell it, hiding the fact that it was in fact just HSQLDB. It seems 'bungisoft' does not exist any more, but you can use the Wayback Machine of http://www.archive.org and visit old web pages of http://www.bungisoft.com .

@license_1009_p
About porting the source code to another language (for example C# or C++): Converted source code (even if done manually) stays under the same copyright and license as the original code. The copyright of the ported source code does not (automatically) go to the person who ported the code.

@license_1010_h2
H2 License, Version 1.0

@license_1011_h3
1. Definitions

@license_1012_b
1.0.1. "Commercial Use"

@license_1013_p
means distribution or otherwise making the Covered Code available to a third party.

@license_1014_b
1.1. "Contributor"

@license_1015_p
means each entity that creates or contributes to the creation of Modifications.

@license_1016_b
1.2. "Contributor Version"

@license_1017_p
means the combination of the Original Code, prior Modifications used by a Contributor, and the Modifications made by that particular Contributor.

@license_1018_b
1.3. "Covered Code"

@license_1019_p
means the Original Code or Modifications or the combination of the Original Code and Modifications, in each case including portions thereof.

@license_1020_b
1.4. "Electronic Distribution Mechanism"

@license_1021_p
means a mechanism generally accepted in the software development community for the electronic transfer of data.

@license_1022_b
1.5. "Executable"

@license_1023_p
means Covered Code in any form other than Source Code.

@license_1024_b
1.6. "Initial Developer"

@license_1025_p
means the individual or entity identified as the Initial Developer in the Source Code notice required by <a href="#exhibit-a">Exhibit A</a> .

@license_1026_b
1.7. "Larger Work"

@license_1027_p
means a work which combines Covered Code or portions thereof with code not governed by the terms of this License.

@license_1028_b
1.8. "License"

@license_1029_p
means this document.

@license_1030_b
1.8.1. "Licensable"

@license_1031_p
means having the right to grant, to the maximum extent possible, whether at the time of the initial grant or subsequently acquired, any and all of the rights conveyed herein.

@license_1032_b
1.9. "Modifications"

@license_1033_p
means any addition to or deletion from the substance or structure of either the Original Code or any previous Modifications. When Covered Code is released as a series of files, a Modification is:

@license_1034_p
1.9.a. Any addition to or deletion from the contents of a file containing Original Code or previous Modifications.

@license_1035_p
1.9.b. Any new file that contains any part of the Original Code or previous Modifications.

@license_1036_b
1.10. "Original Code"

@license_1037_p
means Source Code of computer software code which is described in the Source Code notice required by <a href="#exhibit-a">Exhibit A</a> as Original Code, and which, at the time of its release under this License is not already Covered Code governed by this License.

@license_1038_b
1.10.1. "Patent Claims"

@license_1039_p
means any patent claim(s), now owned or hereafter acquired, including without limitation, method, process, and apparatus claims, in any patent Licensable by grantor.

@license_1040_b
1.11. "Source Code"

@license_1041_p
means the preferred form of the Covered Code for making modifications to it, including all modules it contains, plus any associated interface definition files, scripts used to control compilation and installation of an Executable, or source code differential comparisons against either the Original Code or another well known, available Covered Code of the Contributor's choice. The Source Code can be in a compressed or archival form, provided the appropriate decompression or de-archiving software is widely available for no charge.

@license_1042_b
1.12. "You" (or "Your")

@license_1043_p
means an individual or a legal entity exercising rights under, and complying with all of the terms of, this License or a future version of this License issued under <a href="#section-6.1">Section 6.1.</a> For legal entities, "You" includes any entity which controls, is controlled by, or is under common control with You. For purposes of this definition, "control" means (a) the power, direct or indirect, to cause the direction or management of such entity, whether by contract or otherwise, or (b) ownership of more than fifty percent (50%) of the outstanding shares or beneficial ownership of such entity.

@license_1044_h3
2. Source Code License

@license_1045_h4
2.1. The Initial Developer Grant

@license_1046_p
The Initial Developer hereby grants You a world-wide, royalty-free, non-exclusive license, subject to third party intellectual property claims:

@license_1047_p
2.1.a. under intellectual property rights (other than patent or trademark) Licensable by Initial Developer to use, reproduce, modify, display, perform, sublicense and distribute the Original Code (or portions thereof) with or without Modifications, and/or as part of a Larger Work; and

@license_1048_p
2.1.b. under Patents Claims infringed by the making, using or selling of Original Code, to make, have made, use, practice, sell, and offer for sale, and/or otherwise dispose of the Original Code (or portions thereof).

@license_1049_p
2.1.c. the licenses granted in this Section 2.1 ( <a href="#section-2.1-a">a</a> ) and ( <a href="#section-2.1-b">b</a> ) are effective on the date Initial Developer first distributes Original Code under the terms of this License.

@license_1050_p
2.1.d. Notwithstanding Section 2.1 ( <a href="#section-2.1-b">b</a> ) above, no patent license is granted: 1) for code that You delete from the Original Code; 2) separate from the Original Code; or 3) for infringements caused by: i) the modification of the Original Code or ii) the combination of the Original Code with other software or devices.

@license_1051_h4
2.2. Contributor Grant

@license_1052_p
Subject to third party intellectual property claims, each Contributor hereby grants You a world-wide, royalty-free, non-exclusive license

@license_1053_p
2.2.a. under intellectual property rights (other than patent or trademark) Licensable by Contributor, to use, reproduce, modify, display, perform, sublicense and distribute the Modifications created by such Contributor (or portions thereof) either on an unmodified basis, with other Modifications, as Covered Code and/or as part of a Larger Work; and

@license_1054_p
2.2.b. under Patent Claims infringed by the making, using, or selling of Modifications made by that Contributor either alone and/or in combination with its Contributor Version (or portions of such combination), to make, use, sell, offer for sale, have made, and/or otherwise dispose of: 1) Modifications made by that Contributor (or portions thereof); and 2) the combination of Modifications made by that Contributor with its Contributor Version (or portions of such combination).

@license_1055_p
2.2.c. the licenses granted in Sections 2.2 ( <a href="#section-2.2-a">a</a> ) and 2.2 ( <a href="#section-2.2-b">b</a> ) are effective on the date Contributor first makes Commercial Use of the Covered Code.

@license_1056_p
2.2.c. Notwithstanding Section 2.2 ( <a href="#section-2.2-b">b</a> ) above, no patent license is granted: 1) for any code that Contributor has deleted from the Contributor Version; 2) separate from the Contributor Version; 3) for infringements caused by: i) third party modifications of Contributor Version or ii) the combination of Modifications made by that Contributor with other software (except as part of the Contributor Version) or other devices; or 4) under Patent Claims infringed by Covered Code in the absence of Modifications made by that Contributor.

@license_1057_h3
3. Distribution Obligations

@license_1058_h4
3.1. Application of License

@license_1059_p
The Modifications which You create or to which You contribute are governed by the terms of this License, including without limitation Section <a href="#section-2.2">2.2</a> . The Source Code version of Covered Code may be distributed only under the terms of this License or a future version of this License released under Section <a href="#section-6.1">6.1</a> , and You must include a copy of this License with every copy of the Source Code You distribute. You may not offer or impose any terms on any Source Code version that alters or restricts the applicable version of this License or the recipients' rights hereunder. However, You may include an additional document offering the additional rights described in Section <a href="#section-3.5">3.5</a> .

@license_1060_h4
3.2. Availability of Source Code

@license_1061_p
Any Modification which You create or to which You contribute must be made available in Source Code form under the terms of this License either on the same media as an Executable version or via an accepted Electronic Distribution Mechanism to anyone to whom you made an Executable version available; and if made available via Electronic Distribution Mechanism, must remain available for at least twelve (12) months after the date it initially became available, or at least six (6) months after a subsequent version of that particular Modification has been made available to such recipients. You are responsible for ensuring that the Source Code version remains available even if the Electronic Distribution Mechanism is maintained by a third party.

@license_1062_h4
3.3. Description of Modifications

@license_1063_p
You must cause all Covered Code to which You contribute to contain a file documenting the changes You made to create that Covered Code and the date of any change. You must include a prominent statement that the Modification is derived, directly or indirectly, from Original Code provided by the Initial Developer and including the name of the Initial Developer in (a) the Source Code, and (b) in any notice in an Executable version or related documentation in which You describe the origin or ownership of the Covered Code.

@license_1064_h4
3.4. Intellectual Property Matters

@license_1065_b
3.4.a. Third Party Claims:

@license_1066_p
If Contributor has knowledge that a license under a third party's intellectual property rights is required to exercise the rights granted by such Contributor under Sections <a href="#section-2.1">2.1</a> or <a href="#section-2.2">2.2</a> , Contributor must include a text file with the Source Code distribution titled "LEGAL" which describes the claim and the party making the claim in sufficient detail that a recipient will know whom to contact. If Contributor obtains such knowledge after the Modification is made available as described in Section <a href="#section-3.2">3.2</a> , Contributor shall promptly modify the LEGAL file in all copies Contributor makes available thereafter and shall take other steps (such as notifying appropriate mailing lists or newsgroups) reasonably calculated to inform those who received the Covered Code that new knowledge has been obtained.

@license_1067_b
3.4.b. Contributor APIs:

@license_1068_p
If Contributor's Modifications include an application programming interface and Contributor has knowledge of patent licenses which are reasonably necessary to implement that API, Contributor must also include this information in the legal file.

@license_1069_b
3.4.c. Representations:

@license_1070_p
Contributor represents that, except as disclosed pursuant to Section 3.4 ( <a href="#section-3.4-a">a</a> ) above, Contributor believes that Contributor's Modifications are Contributor's original creation(s) and/or Contributor has sufficient rights to grant the rights conveyed by this License.

@license_1071_h4
3.5. Required Notices

@license_1072_p
You must duplicate the notice in <a href="#exhibit-a">Exhibit A</a> in each file of the Source Code. If it is not possible to put such notice in a particular Source Code file due to its structure, then You must include such notice in a location (such as a relevant directory) where a user would be likely to look for such a notice. If You created one or more Modification(s) You may add your name as a Contributor to the notice described in <a href="#exhibit-a">Exhibit A</a> . You must also duplicate this License in any documentation for the Source Code where You describe recipients' rights or ownership rights relating to Covered Code. You may choose to offer, and to charge a fee for, warranty, support, indemnity or liability obligations to one or more recipients of Covered Code. However, You may do so only on Your own behalf, and not on behalf of the Initial Developer or any Contributor. You must make it absolutely clear than any such warranty, support, indemnity or liability obligation is offered by You alone, and You hereby agree to indemnify the Initial Developer and every Contributor for any liability incurred by the Initial Developer or such Contributor as a result of warranty, support, indemnity or liability terms You offer.

@license_1073_h4
3.6. Distribution of Executable Versions

@license_1074_p
You may distribute Covered Code in Executable form only if the requirements of Sections <a href="#section-3.1">3.1</a> , <a href="#section-3.2">3.2</a> , <a href="#section-3.3">3.3</a> , <a href="#section-3.4">3.4</a> and <a href="#section-3.5">3.5</a> have been met for that Covered Code, and if You include a notice stating that the Source Code version of the Covered Code is available under the terms of this License, including a description of how and where You have fulfilled the obligations of Section <a href="#section-3.2">3.2</a> . The notice must be conspicuously included in any notice in an Executable version, related documentation or collateral in which You describe recipients' rights relating to the Covered Code. You may distribute the Executable version of Covered Code or ownership rights under a license of Your choice, which may contain terms different from this License, provided that You are in compliance with the terms of this License and that the license for the Executable version does not attempt to limit or alter the recipient's rights in the Source Code version from the rights set forth in this License. If You distribute the Executable version under a different license You must make it absolutely clear that any terms which differ from this License are offered by You alone, not by the Initial Developer or any Contributor. You hereby agree to indemnify the Initial Developer and every Contributor for any liability incurred by the Initial Developer or such Contributor as a result of any such terms You offer.

@license_1075_h4
3.7. Larger Works

@license_1076_p
You may create a Larger Work by combining Covered Code with other code not governed by the terms of this License and distribute the Larger Work as a single product. In such a case, You must make sure the requirements of this License are fulfilled for the Covered Code.

@license_1077_h3
4. Inability to Comply Due to Statute or Regulation.

@license_1078_p
If it is impossible for You to comply with any of the terms of this License with respect to some or all of the Covered Code due to statute, judicial order, or regulation then You must: (a) comply with the terms of this License to the maximum extent possible; and (b) describe the limitations and the code they affect. Such description must be included in the <b>legal</b> file described in Section <a href="#section-3.4">3.4</a> and must be included with all distributions of the Source Code. Except to the extent prohibited by statute or regulation, such description must be sufficiently detailed for a recipient of ordinary skill to be able to understand it.

@license_1079_h3
5. Application of this License.

@license_1080_p
This License applies to code to which the Initial Developer has attached the notice in <a href="#exhibit-a">Exhibit A</a> and to related Covered Code.

@license_1081_h3
6. Versions of the License.

@license_1082_h4
6.1. New Versions

@license_1083_p
The

@license_1084_em
H2 Group</em> may publish revised and/or new versions of the License from time to time. Each version will be given a distinguishing version number.

@license_1085_h4
6.2. Effect of New Versions

@license_1086_p
Once Covered Code has been published under a particular version of the License, You may always continue to use it under the terms of that version. You may also choose to use such Covered Code under the terms of any subsequent version of the License published by the

@license_1087_em
H2 Group</em> . No one other than the

@license_1088_em
H2 Group</em> has the right to modify the terms applicable to Covered Code created under this License.

@license_1089_h4
6.3. Derivative Works

@license_1090_p
If You create or use a modified version of this License (which you may only do in order to apply it to code which is not already Covered Code governed by this License), You must (a) rename Your license so that the phrases

@license_1091_em
"H2 Group", "H2"</em> or any confusingly similar phrase do not appear in your license (except to note that your license differs from this License) and (b) otherwise make it clear that Your version of the license contains terms which differ from the

@license_1092_em
H2 License</em> . (Filling in the name of the Initial Developer, Original Code or Contributor in the notice described in <a href="#exhibit-a">Exhibit A</a> shall not of themselves be deemed to be modifications of this License.)

@license_1093_h3
7. Disclaimer of Warranty

@license_1094_p
Covered code is provided under this license on an "as is" basis, without warranty of any kind, either expressed or implied, including, without limitation, warranties that the covered code is free of defects, merchantable, fit for a particular purpose or non-infringing. The entire risk as to the quality and performance of the covered code is with you. Should any covered code prove defective in any respect, you (not the initial developer or any other contributor) assume the cost of any necessary servicing, repair or correction. This disclaimer of warranty constitutes an essential part of this license. No use of any covered code is authorized hereunder except under this disclaimer.

@license_1095_h3
8. Termination

@license_1096_p
8.1. This License and the rights granted hereunder will terminate automatically if You fail to comply with terms herein and fail to cure such breach within 30 days of becoming aware of the breach. All sublicenses to the Covered Code which are properly granted shall survive any termination of this License. Provisions which, by their nature, must remain in effect beyond the termination of this License shall survive.

@license_1097_p
8.2. If You initiate litigation by asserting a patent infringement claim (excluding declaratory judgment actions) against Initial Developer or a Contributor (the Initial Developer or Contributor against whom You file such action is referred to as "Participant") alleging that:

@license_1098_p
8.2.a. such Participant's Contributor Version directly or indirectly infringes any patent, then any and all rights granted by such Participant to You under Sections <a href="#section-2.1">2.1</a> and/or <a href="#section-2.2">2.2</a> of this License shall, upon 60 days notice from Participant terminate prospectively, unless if within 60 days after receipt of notice You either: (i) agree in writing to pay Participant a mutually agreeable reasonable royalty for Your past and future use of Modifications made by such Participant, or (ii) withdraw Your litigation claim with respect to the Contributor Version against such Participant. If within 60 days of notice, a reasonable royalty and payment arrangement are not mutually agreed upon in writing by the parties or the litigation claim is not withdrawn, the rights granted by Participant to You under Sections <a href="#section-2.1">2.1</a> and/or <a href="#section-2.2">2.2</a> automatically terminate at the expiration of the 60 day notice period specified above.

@license_1099_p
8.2.b. any software, hardware, or device, other than such Participant's Contributor Version, directly or indirectly infringes any patent, then any rights granted to You by such Participant under Sections 2.1( <a href="#section-2.1-b">b</a> ) and 2.2( <a href="#section-2.2-b">b</a> ) are revoked effective as of the date You first made, used, sold, distributed, or had made, Modifications made by that Participant.

@license_1100_p
8.3. If You assert a patent infringement claim against Participant alleging that such Participant's Contributor Version directly or indirectly infringes any patent where such claim is resolved (such as by license or settlement) prior to the initiation of patent infringement litigation, then the reasonable value of the licenses granted by such Participant under Sections <a href="#section-2.1">2.1</a> or <a href="#section-2.2">2.2</a> shall be taken into account in determining the amount or value of any payment or license.

@license_1101_p
8.4. In the event of termination under Sections <a href="#section-8.1">8.1</a> or <a href="#section-8.2">8.2</a> above, all end user license agreements (excluding distributors and resellers) which have been validly granted by You or any distributor hereunder prior to termination shall survive termination.

@license_1102_h3
9. Limitation of Liability

@license_1103_p
Under no circumstances and under no legal theory, whether tort (including negligence), contract, or otherwise, shall you, the initial developer, any other contributor, or any distributor of covered code, or any supplier of any of such parties, be liable to any person for any indirect, special, incidental, or consequential damages of any character including, without limitation, damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses, even if such party shall have been informed of the possibility of such damages. This limitation of liability shall not apply to liability for death or personal injury resulting from such party's negligence to the extent applicable law prohibits such limitation. Some jurisdictions do not allow the exclusion or limitation of incidental or consequential damages, so this exclusion and limitation may not apply to you.

@license_1104_h3
10. United States Government End Users

@license_1105_p
The Covered Code is a "commercial item", as that term is defined in 48 C.F.R. 2.101 (October 1995), consisting of "commercial computer software" and "commercial computer software documentation", as such terms are used in 48 C.F.R. 12.212 (September 1995). Consistent with 48 C.F.R. 12.212 and 48 C.F.R. 227.7202-1 through 227.7202-4 (June 1995), all U.S. Government End Users acquire Covered Code with only those rights set forth herein.

@license_1106_h3
11. Miscellaneous

@license_1107_p
This License represents the complete agreement concerning subject matter hereof. If any provision of this License is held to be unenforceable, such provision shall be reformed only to the extent necessary to make it enforceable. This License shall be governed by California law provisions (except to the extent applicable law, if any, provides otherwise), excluding its conflict-of-law provisions. With respect to disputes in which at least one party is a citizen of, or an entity chartered or registered to do business in United States of America, any litigation relating to this License shall be subject to the jurisdiction of the Federal Courts of the Northern District of California, with venue lying in Santa Clara County, California, with the losing party responsible for costs, including without limitation, court costs and reasonable attorneys' fees and expenses. The application of the United Nations Convention on Contracts for the International Sale of Goods is expressly excluded. Any law or regulation which provides that the language of a contract shall be construed against the drafter shall not apply to this License.

@license_1108_h3
12. Responsibility for Claims

@license_1109_p
As between Initial Developer and the Contributors, each party is responsible for claims and damages arising, directly or indirectly, out of its utilization of rights under this License and You agree to work with Initial Developer and Contributors to distribute such responsibility on an equitable basis. Nothing herein is intended or shall be deemed to constitute any admission of liability.

@license_1110_h3
13. Multiple-Licensed Code

@license_1111_p
Initial Developer may designate portions of the Covered Code as "Multiple-Licensed". "Multiple-Licensed" means that the Initial Developer permits you to utilize portions of the Covered Code under Your choice of this or the alternative licenses, if any, specified by the Initial Developer in the file described in <a href="#exhibit-a">Exhibit A</a> .

@license_1112_h3
Exhibit A

@license_1113_h2
Eclipse Public License - Version 1.0

@license_1114_p
THE ACCOMPANYING PROGRAM IS PROVIDED UNDER THE TERMS OF THIS ECLIPSE PUBLIC LICENSE ("AGREEMENT"). ANY USE, REPRODUCTION OR DISTRIBUTION OF THE PROGRAM CONSTITUTES RECIPIENT'S ACCEPTANCE OF THIS AGREEMENT.

@license_1115_h3
1. DEFINITIONS

@license_1116_p
"Contribution" means:

@license_1117_p
a) in the case of the initial Contributor, the initial code and documentation distributed under this Agreement, and

@license_1118_p
b) in the case of each subsequent Contributor:

@license_1119_p
i) changes to the Program, and

@license_1120_p
ii) additions to the Program;

@license_1121_p
where such changes and/or additions to the Program originate from and are distributed by that particular Contributor. A Contribution 'originates' from a Contributor if it was added to the Program by such Contributor itself or anyone acting on such Contributor's behalf. Contributions do not include additions to the Program which: (i) are separate modules of software distributed in conjunction with the Program under their own license agreement, and (ii) are not derivative works of the Program.

@license_1122_p
"Contributor" means any person or entity that distributes the Program.

@license_1123_p
"Licensed Patents " mean patent claims licensable by a Contributor which are necessarily infringed by the use or sale of its Contribution alone or when combined with the Program.

@license_1124_p
"Program" means the Contributions distributed in accordance with this Agreement.

@license_1125_p
"Recipient" means anyone who receives the Program under this Agreement, including all Contributors.

@license_1126_h3
2. GRANT OF RIGHTS

@license_1127_p
a) Subject to the terms of this Agreement, each Contributor hereby grants Recipient a non-exclusive, worldwide, royalty-free copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, distribute and sublicense the Contribution of such Contributor, if any, and such derivative works, in source code and object code form.

@license_1128_p
b) Subject to the terms of this Agreement, each Contributor hereby grants Recipient a non-exclusive, worldwide, royalty-free patent license under Licensed Patents to make, use, sell, offer to sell, import and otherwise transfer the Contribution of such Contributor, if any, in source code and object code form. This patent license shall apply to the combination of the Contribution and the Program if, at the time the Contribution is added by the Contributor, such addition of the Contribution causes such combination to be covered by the Licensed Patents. The patent license shall not apply to any other combinations which include the Contribution. No hardware per se is licensed hereunder.

@license_1129_p
c) Recipient understands that although each Contributor grants the licenses to its Contributions set forth herein, no assurances are provided by any Contributor that the Program does not infringe the patent or other intellectual property rights of any other entity. Each Contributor disclaims any liability to Recipient for claims brought by any other entity based on infringement of intellectual property rights or otherwise. As a condition to exercising the rights and licenses granted hereunder, each Recipient hereby assumes sole responsibility to secure any other intellectual property rights needed, if any. For example, if a third party patent license is required to allow Recipient to distribute the Program, it is Recipient's responsibility to acquire that license before distributing the Program.

@license_1130_p
d) Each Contributor represents that to its knowledge it has sufficient copyright rights in its Contribution, if any, to grant the copyright license set forth in this Agreement.

@license_1131_h3
3. REQUIREMENTS

@license_1132_p
A Contributor may choose to distribute the Program in object code form under its own license agreement, provided that:

@license_1133_p
a) it complies with the terms and conditions of this Agreement; and

@license_1134_p
b) its license agreement:

@license_1135_p
i) effectively disclaims on behalf of all Contributors all warranties and conditions, express and implied, including warranties or conditions of title and non-infringement, and implied warranties or conditions of merchantability and fitness for a particular purpose;

@license_1136_p
ii) effectively excludes on behalf of all Contributors all liability for damages, including direct, indirect, special, incidental and consequential damages, such as lost profits;

@license_1137_p
iii) states that any provisions which differ from this Agreement are offered by that Contributor alone and not by any other party; and

@license_1138_p
iv) states that source code for the Program is available from such Contributor, and informs licensees how to obtain it in a reasonable manner on or through a medium customarily used for software exchange.

@license_1139_p
When the Program is made available in source code form:

@license_1140_p
a) it must be made available under this Agreement; and

@license_1141_p
b) a copy of this Agreement must be included with each copy of the Program.

@license_1142_p
Contributors may not remove or alter any copyright notices contained within the Program.

@license_1143_p
Each Contributor must identify itself as the originator of its Contribution, if any, in a manner that reasonably allows subsequent Recipients to identify the originator of the Contribution.

@license_1144_h3
4. COMMERCIAL DISTRIBUTION

@license_1145_p
Commercial distributors of software may accept certain responsibilities with respect to end users, business partners and the like. While this license is intended to facilitate the commercial use of the Program, the Contributor who includes the Program in a commercial product offering should do so in a manner which does not create potential liability for other Contributors. Therefore, if a Contributor includes the Program in a commercial product offering, such Contributor ("Commercial Contributor") hereby agrees to defend and indemnify every other Contributor ("Indemnified Contributor") against any losses, damages and costs (collectively "Losses") arising from claims, lawsuits and other legal actions brought by a third party against the Indemnified Contributor to the extent caused by the acts or omissions of such Commercial Contributor in connection with its distribution of the Program in a commercial product offering. The obligations in this section do not apply to any claims or Losses relating to any actual or alleged intellectual property infringement. In order to qualify, an Indemnified Contributor must: a) promptly notify the Commercial Contributor in writing of such claim, and b) allow the Commercial Contributor to control, and cooperate with the Commercial Contributor in, the defense and any related settlement negotiations. The Indemnified Contributor may participate in any such claim at its own expense.

@license_1146_p
For example, a Contributor might include the Program in a commercial product offering, Product X. That Contributor is then a Commercial Contributor. If that Commercial Contributor then makes performance claims, or offers warranties related to Product X, those performance claims and warranties are such Commercial Contributor's responsibility alone. Under this section, the Commercial Contributor would have to defend claims against the other Contributors related to those performance claims and warranties, and if a court requires any other Contributor to pay any damages as a result, the Commercial Contributor must pay those damages.

@license_1147_h3
5. NO WARRANTY

@license_1148_p
EXCEPT AS EXPRESSLY SET FORTH IN THIS AGREEMENT, THE PROGRAM IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED INCLUDING, WITHOUT LIMITATION, ANY WARRANTIES OR CONDITIONS OF TITLE, NON-INFRINGEMENT, MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Each Recipient is solely responsible for determining the appropriateness of using and distributing the Program and assumes all risks associated with its exercise of rights under this Agreement, including but not limited to the risks and costs of program errors, compliance with applicable laws, damage to or loss of data, programs or equipment, and unavailability or interruption of operations.

@license_1149_h3
6. DISCLAIMER OF LIABILITY

@license_1150_p
EXCEPT AS EXPRESSLY SET FORTH IN THIS AGREEMENT, NEITHER RECIPIENT NOR ANY CONTRIBUTORS SHALL HAVE ANY LIABILITY FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING WITHOUT LIMITATION LOST PROFITS), HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OR DISTRIBUTION OF THE PROGRAM OR THE EXERCISE OF ANY RIGHTS GRANTED HEREUNDER, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

@license_1151_h3
7. GENERAL

@license_1152_p
If any provision of this Agreement is invalid or unenforceable under applicable law, it shall not affect the validity or enforceability of the remainder of the terms of this Agreement, and without further action by the parties hereto, such provision shall be reformed to the minimum extent necessary to make such provision valid and enforceable.

@license_1153_p
If Recipient institutes patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that the Program itself (excluding combinations of the Program with other software or hardware) infringes such Recipient's patent(s), then such Recipient's rights granted under Section 2(b) shall terminate as of the date such litigation is filed.

@license_1154_p
All Recipient's rights under this Agreement shall terminate if it fails to comply with any of the material terms or conditions of this Agreement and does not cure such failure in a reasonable period of time after becoming aware of such noncompliance. If all Recipient's rights under this Agreement terminate, Recipient agrees to cease use and distribution of the Program as soon as reasonably practicable. However, Recipient's obligations under this Agreement and any licenses granted by Recipient relating to the Program shall continue and survive.

@license_1155_p
Everyone is permitted to copy and distribute copies of this Agreement, but in order to avoid inconsistency the Agreement is copyrighted and may only be modified in the following manner. The Agreement Steward reserves the right to publish new versions (including revisions) of this Agreement from time to time. No one other than the Agreement Steward has the right to modify this Agreement. The Eclipse Foundation is the initial Agreement Steward. The Eclipse Foundation may assign the responsibility to serve as the Agreement Steward to a suitable separate entity. Each new version of the Agreement will be given a distinguishing version number. The Program (including Contributions) may always be distributed subject to the version of the Agreement under which it was received. In addition, after a new version of the Agreement is published, Contributor may elect to distribute the Program (including its Contributions) under the new version. Except as expressly stated in Sections 2(a) and 2(b) above, Recipient receives no rights or licenses to the intellectual property of any Contributor under this Agreement, whether expressly, by implication, estoppel or otherwise. All rights in the Program not expressly granted under this Agreement are reserved.

@license_1156_p
This Agreement is governed by the laws of the State of New York and the intellectual property laws of the United States of America. No party to this Agreement will bring a legal action under this Agreement more than one year after the cause of action arose. Each party waives its rights to a jury trial in any resulting litigation.

@links_1000_h1
H2 In Use and Links

@links_1001_p
Those are just a few links to products using or supporting H2. If you want to add a link, please send it to the support email address or post it in the group.

@links_1002_h2
Books

@links_1003_a
Seam In Action

@links_1004_h2
Extensions

@links_1005_a
Grails H2 Database Plugin

@links_1006_a
h2osgi: OSGi for the H2 Database

@links_1007_a
H2Sharp: ADO.NET interface for the H2 database engine

@links_1008_a
H2 Spatial: spatial functions to H2 database

@links_1009_h2
Blogs

@links_1010_a
Porting Flexive to the H2 Database (2008-12-05)

@links_1011_a
H2 Database with GlassFish (2008-11-24)

@links_1012_a
Using H2 Database with Glassfish and Toplink (2008-08-07)

@links_1013_a
H2 Database - Performance Tracing (2008-04-30)

@links_1014_a
Testing your JDBC data access layer with DBUnit and H2 (2007-09-18)

@links_1015_a
Open Source Databases Comparison (2007-09-11)

@links_1016_a
The Codist: The Open Source Frameworks I Use (2007-07-23)

@links_1017_a
The Codist:  SQL Injections: How Not To Get Stuck (2007-05-08)

@links_1018_a
One Man Band: (Helma + H2) == "to easy" (2007-03-11)

@links_1019_a
David Coldrick's Weblog: New Version of H2 Database Released (2007-01-06)

@links_1020_a
The Codist: Write Your Own Database, Again (2006-11-13)

@links_1021_h2
Project Pages

@links_1022_a
Ohloh

@links_1023_a
Freshmeat Project Page

@links_1024_a
Wikipedia

@links_1025_a
Java Source Net

@links_1026_a
Linux Package Manager

@links_1027_h2
Database Frontends / Tools

@links_1028_a
DB Solo

@links_1029_p
SQL query tool.

@links_1030_a
DbVisualizer

@links_1031_p
Database tool.

@links_1032_a
Execute Query

@links_1033_p
Database utility written in Java.

@links_1034_a
[fleXive]

@links_1035_p
JavaEE 5 open source framework for the development of complex and evolving (web-)applications.

@links_1036_a
HenPlus

@links_1037_p
HenPlus is a SQL shell written in Java.

@links_1038_a
RazorSQL

@links_1039_p
An SQL query tool, database browser, SQL editor, and database administration tool.

@links_1040_a
SQL Developer

@links_1041_p
Universal Database Frontend.

@links_1042_a
SQL Workbench/J

@links_1043_p
Free DBMS-independent SQL tool.

@links_1044_a
SQuirreL SQL Client

@links_1045_p
Graphical tool to view the structure of a database, browse the data, issue SQL commands etc.

@links_1046_a
SQuirreL DB Copy Plugin

@links_1047_p
Tool to copy data from one database to another.

@links_1048_h2
Products and Projects

@links_1049_a
&AElig;jaks

@links_1050_p
A server-side scripting environment to build AJAX enabled web applications.

@links_1051_a
Axiom Stack

@links_1052_p
A web framework that let's you write dynamic web applications with Zen-like simplicity.

@links_1053_a
Apache Cayenne

@links_1054_p
Open source persistence framework providing object-relational mapping (ORM) and remoting services.

@links_1055_a
Apache Jackrabbit

@links_1056_p
Open source implementation of the Java Content Repository API (JCR).

@links_1057_a
Apache OpenJPA

@links_1058_p
Open source implementation of the Java Persistence API (JPA).

@links_1059_a
AppFuse

@links_1060_p
Helps building web applications.

@links_1061_a
BGBlitz

@links_1062_p
The Swiss army knife of Backgammon.

@links_1063_a
Blojsom

@links_1064_p
Java-based multi-blog, multi-user software package (Mac OS X Weblog Server).

@links_1065_a
Bonita

@links_1066_p
Open source workflow solution for handing long-running, user-oriented processes providing out of the box workflow and business process management features.

@links_1067_a
Bookmarks Portlet

@links_1068_p
JSR 168 compliant bookmarks management portlet application.

@links_1069_a
Claros inTouch

@links_1070_p
Ajax communication suite with mail, addresses, notes, IM, and rss reader.

@links_1071_a
CrashPlan PRO Server

@links_1072_p
Easy and cross platform backup solution for business and service providers.

@links_1073_a
DbUnit

@links_1074_p
A JUnit extension (also usable with Ant) targeted for database-driven projects.

@links_1075_a
Ebean ORM Persistence Layer

@links_1076_p
Open source Java Object Relational Mapping tool.

@links_1077_a
Epictetus

@links_1078_p
Free cross platform database tool.

@links_1079_a
Fabric3

@links_1080_p
Fabric3 is a project implementing a federated service network based on the Service Component Architecture specification (http://www.osoa.org).

@links_1081_a
FIT4Data

@links_1082_p
A testing framework for data management applications built on the Java implementation of FIT.

@links_1083_a
Flux

@links_1084_p
Java job scheduler, file transfer, workflow, and BPM.

@links_1085_a
GNU Gluco Control

@links_1086_p
Helps you to manage your diabetes.

@links_1087_a
Golden T Studios

@links_1088_p
Fun-to-play games with a simple interface.

@links_1089_a
Group Session

@links_1090_p
Open source web groupware.

@links_1091_a
HA-JDBC

@links_1092_p
High-Availability JDBC: A JDBC proxy that provides light-weight, transparent, fault tolerant clustering capability to any underlying JDBC driver.

@links_1093_a
Harbor

@links_1094_p
Pojo Application Server.

@links_1095_a
Hibernate

@links_1096_p
Relational persistence for idiomatic Java (O-R mapping tool).

@links_1097_a
Hibicius

@links_1098_p
Online Banking Client for the HBCI protocol.

@links_1099_a
ImageMapper

@links_1100_p
ImageMapper frees users from having to use file browsers to view their images. They get fast access to images and easy cataloguing of them via a user friendly interface.

@links_1101_a
JAMWiki

@links_1102_p
Java-based Wiki engine.

@links_1103_a
Jala

@links_1104_p
Open source collection of JavaScript modules.

@links_1105_a
Java Simon

@links_1106_p
Simple Monitoring API.

@links_1107_a
jBPM

@links_1108_p
A platform for executable process languages ranging from business process management (BPM) over workflow to service orchestration.

@links_1109_a
JGeocoder

@links_1110_p
Free Java geocoder. Geocoding is the process of estimating a latitude and longitude for a given location.

@links_1111_a
JGrass

@links_1112_p
Java Geographic Resources Analysis Support System. Free, multi platform, open source GIS based on the GIS framework of uDig.

@links_1113_a
Jena

@links_1114_p
Java framework for building Semantic Web applications.

@links_1115_a
JMatter

@links_1116_p
Framework for constructing workgroup business applications based on the Naked Objects Architectural Pattern.

@links_1117_a
JotBot

@links_1118_p
Records your day at user defined intervals.

@links_1119_a
JPOX

@links_1120_p
Java persistent objects.

@links_1121_a
Liftweb

@links_1122_p
A Scala-based, secure, developer friendly web framework.

@links_1123_a
LiquiBase

@links_1124_p
A tool to manage database changes and refactorings.

@links_1125_a
Luntbuild

@links_1126_p
Build automation and management tool.

@links_1127_a
localdb

@links_1128_p
A tool that locates the full file path of the folder containing the database files.

@links_1129_a
Magnolia

@links_1130_p
Microarray Data Management and Export System for PFGRC (Pathogen Functional Genomics Resource Center) Microarrays.

@links_1131_a
MiniConnectionPoolManager

@links_1132_p
A lightweight standalone JDBC connection pool manager.

@links_1133_a
Mr. Persister

@links_1134_p
Simple, small and fast object relational mapping.

@links_1135_a
Myna Application Server

@links_1136_p
Java web app that provides dynamic web content and Java libraries access from JavaScript.

@links_1137_a
MyTunesRss

@links_1138_p
MyTunesRSS lets you listen to your music wherever you are.

@links_1139_a
NCGC CurveFit

@links_1140_p
From: NIH Chemical Genomics Center, National Institutes of Health, USA. An open source application in the life sciences research field. This application handles chemical structures and biological responses of thousands of compounds with the potential to handle million+ compounds. It utilizes an embedded H2 database to enable flexible query/retrieval of all data including advanced chemical substructure and similarity searching. The application highlights an automated curve fitting and classification algorithm that outperforms commercial packages in the field. Commercial alternatives are typically small desktop software that handle a few dose response curves at a time. A couple of commercial packages that do handle several thousand curves are very expensive tools (&gt;60k USD) that require manual curation of analysis by the user; require a license to Oracle; lack advanced query/retrieval; and the ability to handle chemical structures.

@links_1141_a
Nuxeo

@links_1142_p
Standards-based, open source platform for building ECM applications.

@links_1143_a
nWire

@links_1144_p
Eclipse plug-in which expedites Java development. It's main purpose is to help developers find code quicker and easily understand how it relates to the rest of the application, thus, understand the application structure.

@links_1145_a
Ontology Works

@links_1146_p
This company provides semantic technologies including deductive information repositories (the Ontology Works Knowledge Servers), semantic information fusion and semantic federation of legacy databases, ontology-based domain modeling, and management of the distributed enterprise.

@links_1147_a
Ontoprise OntoBroker

@links_1148_p
SemanticWeb-Middleware. It supports all W3C Semantic Web recommendations: OWL, RDF, RDFS, SPARQL, and F-Logic.

@links_1149_a
Open Anzo

@links_1150_p
Semantic Application Server.

@links_1151_a
OpenGroove

@links_1152_p
OpenGroove is a groupware program that allows users to synchronize data.

@links_1153_a
OpenSocial Development Environment (OSDE)

@links_1154_p
Development tool for OpenSocial application.

@links_1155_a
Orion

@links_1156_p
J2EE Application Server.

@links_1157_a
P5H2

@links_1158_p
A library for the <a href="http://www.processing.org">Processing</a> programming language and environment.

@links_1159_a
Phase-6

@links_1160_p
A computer based learning software.

@links_1161_a
Pickle

@links_1162_p
Pickle is a Java library containing classes for persistence, concurrency, and logging.

@links_1163_a
Piman

@links_1164_p
Water treatment projects data management.

@links_1165_a
PolePosition

@links_1166_p
Open source database benchmark.

@links_1167_a
Poormans

@links_1168_p
Very basic CMS running as a SWT application and generating static html pages.

@links_1169_a
Railo

@links_1170_p
Railo is an alternative engine for the Cold Fusion Markup Language, that compiles code programmed in CFML into Java bytecode and executes it on a servlet engine.

@links_1171_a
Razuna

@links_1172_p
Open source Digital Asset Management System with integrated Web Content Management.

@links_1173_a
RIFE

@links_1174_p
A full-stack web application framework with tools and APIs to implement most common web features.

@links_1175_a
Rutema

@links_1176_p
Rutema is a test execution and management tool for heterogeneous development environments written in Ruby.

@links_1177_a
Sava

@links_1178_p
Open-source web-based content management system.

@links_1179_a
Scriptella

@links_1180_p
ETL (Extract-Transform-Load) and script execution tool.

@links_1181_a
Sesar

@links_1182_p
Dependency Injection Container with Aspect Oriented Programming.

@links_1183_a
SemmleCode

@links_1184_p
Eclipse plugin to help you improve software quality.

@links_1185_a
SeQuaLite

@links_1186_p
A free, light-weight, java data access framework.

@links_1187_a
ShapeLogic

@links_1188_p
Toolkit for declarative programming, image processing and computer vision.

@links_1189_a
Shellbook

@links_1190_p
Desktop publishing application.

@links_1191_a
Signsoft intelliBO

@links_1192_p
Persistence middleware supporting the JDO specification.

@links_1193_a
SimpleORM

@links_1194_p
Simple Java Object Relational Mapping.

@links_1195_a
SymmetricDS

@links_1196_p
A web-enabled, database independent, data synchronization/replication software.

@links_1197_a
SmartFoxServer

@links_1198_p
Platform for developing multiuser applications and games with Macromedia Flash.

@links_1199_a
Social Bookmarks Friend Finder

@links_1200_p
A GUI application that allows you to find users with similar bookmarks to the user specified (for delicious.com).

@links_1201_a
Springfuse

@links_1202_p
Code generation For Spring, Spring MVC & Hibernate.

@links_1203_a
SQLOrm

@links_1204_p
Java Object Relation Mapping.

@links_1205_a
StorYBook

@links_1206_p
A summary-based tool for novelist and script writers. It helps to keep the overview over the various traces a story has.

@links_1207_a
StreamCruncher

@links_1208_p
Event (stream) processing kernel.

@links_1209_a
Tune Backup

@links_1210_p
Easy-to-use backup solution for your iTunes library.

@links_1211_a
weblica

@links_1212_p
Desktop CMS.

@links_1213_a
Web of Web

@links_1214_p
Collaborative and realtime interactive media platform for the web.

@links_1215_a
Werkzeugkasten

@links_1216_p
Minimum Java Toolset.

@links_1217_a
VPDA

@links_1218_p
View providers driven applications is a Java based application framework for building applications composed from server components - view providers.

@links_1219_a
Volunteer database

@links_1220_p
A database front end to register volunteers, partnership and donation for a Non Profit organization.

@mainWeb_1000_h1
H2 Database Engine

@mainWeb_1001_p
Welcome to H2, the Java SQL database. The main feature of H2 are:

@mainWeb_1002_li
Very fast, open source, JDBC API

@mainWeb_1003_li
Embedded and server modes; in-memory databases

@mainWeb_1004_li
Browser based Console application

@mainWeb_1005_li
Small footprint: around 1 MB jar file size

@mainWeb_1006_h3
Download

@mainWeb_1007_td
Version 1.1.113 (2009-05-21):

@mainWeb_1008_a
Windows Installer (3.3 MB)

@mainWeb_1009_a
All Platforms (zip, 4.9 MB)

@mainWeb_1010_a
All Downloads

@mainWeb_1011_td
&nbsp;&nbsp;&nbsp;

@mainWeb_1012_h3
Support

@mainWeb_1013_a
English Google Group

@mainWeb_1014_a
Japanese Google Group

@mainWeb_1015_p
For non-technical issues, use:

@mainWeb_1016_h3
Features

@mainWeb_1017_th
H2

@mainWeb_1018_a
Derby

@mainWeb_1019_a
HSQLDB

@mainWeb_1020_a
MySQL

@mainWeb_1021_a
PostgreSQL

@mainWeb_1022_td
Pure Java

@mainWeb_1023_td
Yes

@mainWeb_1024_td
Yes

@mainWeb_1025_td
Yes

@mainWeb_1026_td
No

@mainWeb_1027_td
No

@mainWeb_1028_td
Memory Mode

@mainWeb_1029_td
Yes

@mainWeb_1030_td
No

@mainWeb_1031_td
Yes

@mainWeb_1032_td
No

@mainWeb_1033_td
No

@mainWeb_1034_td
Transaction Isolation

@mainWeb_1035_td
Yes

@mainWeb_1036_td
Yes

@mainWeb_1037_td
No

@mainWeb_1038_td
Yes

@mainWeb_1039_td
Yes

@mainWeb_1040_td
Cost Based Optimizer

@mainWeb_1041_td
Yes

@mainWeb_1042_td
Yes

@mainWeb_1043_td
No

@mainWeb_1044_td
Yes

@mainWeb_1045_td
Yes

@mainWeb_1046_td
Encrypted Database

@mainWeb_1047_td
Yes

@mainWeb_1048_td
Yes

@mainWeb_1049_td
No

@mainWeb_1050_td
No

@mainWeb_1051_td
No

@mainWeb_1052_td
ODBC Driver

@mainWeb_1053_td
Yes

@mainWeb_1054_td
No

@mainWeb_1055_td
No

@mainWeb_1056_td
Yes

@mainWeb_1057_td
Yes

@mainWeb_1058_td
Fulltext Search

@mainWeb_1059_td
Yes

@mainWeb_1060_td
No

@mainWeb_1061_td
No

@mainWeb_1062_td
Yes

@mainWeb_1063_td
Yes

@mainWeb_1064_td
Multi Version Concurrency

@mainWeb_1065_td
Yes

@mainWeb_1066_td
No

@mainWeb_1067_td
No

@mainWeb_1068_td
No

@mainWeb_1069_td
Yes

@mainWeb_1070_td
Footprint (jar/dll size)

@mainWeb_1071_td
~1 MB

@mainWeb_1072_td
~2 MB

@mainWeb_1073_td
~600 KB

@mainWeb_1074_td
~4 MB

@mainWeb_1075_td
~6 MB

@mainWeb_1076_p
See also the <a href="features.html#comparison">detailed comparison</a> .

@mainWeb_1077_h3
News

@mainWeb_1078_b
Newsfeeds:

@mainWeb_1079_a
Full text (Atom)

@mainWeb_1080_p
or <a href="http://www.h2database.com/html/newsfeed-rss.xml">Header only (RSS)</a> .

@mainWeb_1081_b
Email Newsletter:

@mainWeb_1082_p
Subscribe to <a href="http://groups.google.com/group/h2database-news/subscribe">H2 Database News (Google account required)</a> to get informed about new releases.     Your email address is only used in this context.

@mainWeb_1083_td
&nbsp;

@mainWeb_1084_h3
Contribute

@mainWeb_1085_p
You can contribute to the development of H2 by sending feedback and bug    reports, or translate the H2 Console application (for details, start the H2 Console    and select Options / Translate).    To donate money, click on the PayPal button below. You will be listed as a supporter:

@main_1000_h1
H2 Database Engine

@main_1001_p
Welcome to H2, the free Java SQL database engine.

@main_1002_a
Quickstart

@main_1003_p
Get a fast overview.

@main_1004_a
Tutorial

@main_1005_p
Go through the samples.

@main_1006_a
Features

@main_1007_p
See what this database can do and how to use these features.

@performance_1000_h1
Performance

@performance_1001_a
Performance Comparison

@performance_1002_a
PolePosition Benchmark

@performance_1003_a
Application Profiling

@performance_1004_a
Database Profiling

@performance_1005_a
Performance Tuning

@performance_1006_h2
Performance Comparison

@performance_1007_p
In many cases H2 is faster than other (open source and not open source) database engines. Please note this is mostly a single connection benchmark run on one computer.

@performance_1008_h3
Embedded

@performance_1009_th
Test Case

@performance_1010_th
Unit

@performance_1011_th
H2

@performance_1012_th
HSQLDB

@performance_1013_th
Derby

@performance_1014_td
Simple: Init

@performance_1015_td
ms

@performance_1016_td
610

@performance_1017_td
657

@performance_1018_td
3187

@performance_1019_td
Simple: Query (random)

@performance_1020_td
ms

@performance_1021_td
297

@performance_1022_td
312

@performance_1023_td
1828

@performance_1024_td
Simple: Query (sequential)

@performance_1025_td
ms

@performance_1026_td
203

@performance_1027_td
266

@performance_1028_td
1766

@performance_1029_td
Simple: Update (random)

@performance_1030_td
ms

@performance_1031_td
1078

@performance_1032_td
1484

@performance_1033_td
22031

@performance_1034_td
Simple: Delete (sequential)

@performance_1035_td
ms

@performance_1036_td
234

@performance_1037_td
281

@performance_1038_td
7407

@performance_1039_td
Simple: Memory Usage

@performance_1040_td
MB

@performance_1041_td
6

@performance_1042_td
7

@performance_1043_td
11

@performance_1044_td
BenchA: Init

@performance_1045_td
ms

@performance_1046_td
859

@performance_1047_td
438

@performance_1048_td
4047

@performance_1049_td
BenchA: Transactions

@performance_1050_td
ms

@performance_1051_td
5266

@performance_1052_td
2875

@performance_1053_td
17500

@performance_1054_td
BenchA: Memory Usage

@performance_1055_td
MB

@performance_1056_td
9

@performance_1057_td
14

@performance_1058_td
10

@performance_1059_td
BenchB: Init

@performance_1060_td
ms

@performance_1061_td
4016

@performance_1062_td
2687

@performance_1063_td
16875

@performance_1064_td
BenchB: Transactions

@performance_1065_td
ms

@performance_1066_td
2609

@performance_1067_td
3282

@performance_1068_td
4250

@performance_1069_td
BenchB: Memory Usage

@performance_1070_td
MB

@performance_1071_td
9

@performance_1072_td
10

@performance_1073_td
8

@performance_1074_td
BenchC: Init

@performance_1075_td
ms

@performance_1076_td
891

@performance_1077_td
594

@performance_1078_td
5766

@performance_1079_td
BenchC: Transactions

@performance_1080_td
ms

@performance_1081_td
4359

@performance_1082_td
75438

@performance_1083_td
11718

@performance_1084_td
BenchC: Memory Usage

@performance_1085_td
MB

@performance_1086_td
9

@performance_1087_td
18

@performance_1088_td
9

@performance_1089_td
Executed statements

@performance_1090_td
#

@performance_1091_td
594255

@performance_1092_td
594255

@performance_1093_td
594255

@performance_1094_td
Total time

@performance_1095_td
ms

@performance_1096_td
20422

@performance_1097_td
88314

@performance_1098_td
96375

@performance_1099_td
Statements per second

@performance_1100_td
#

@performance_1101_td
29098

@performance_1102_td
6728

@performance_1103_td
6166

@performance_1104_h3
Client-Server

@performance_1105_th
Test Case

@performance_1106_th
Unit

@performance_1107_th
H2

@performance_1108_th
HSQLDB

@performance_1109_th
Derby

@performance_1110_th
PostgreSQL

@performance_1111_th
MySQL

@performance_1112_td
Simple: Init

@performance_1113_td
ms

@performance_1114_td
3125

@performance_1115_td
3312

@performance_1116_td
7140

@performance_1117_td
5109

@performance_1118_td
3594

@performance_1119_td
Simple: Query (random)

@performance_1120_td
ms

@performance_1121_td
3390

@performance_1122_td
3328

@performance_1123_td
9953

@performance_1124_td
5422

@performance_1125_td
4812

@performance_1126_td
Simple: Query (sequential)

@performance_1127_td
ms

@performance_1128_td
3235

@performance_1129_td
3219

@performance_1130_td
9813

@performance_1131_td
5296

@performance_1132_td
3969

@performance_1133_td
Simple: Update (random)

@performance_1134_td
ms

@performance_1135_td
3437

@performance_1136_td
4562

@performance_1137_td
26594

@performance_1138_td
6766

@performance_1139_td
5703

@performance_1140_td
Simple: Delete (sequential)

@performance_1141_td
ms

@performance_1142_td
1391

@performance_1143_td
1625

@performance_1144_td
9343

@performance_1145_td
2750

@performance_1146_td
2094

@performance_1147_td
Simple: Memory Usage

@performance_1148_td
MB

@performance_1149_td
7

@performance_1150_td
7

@performance_1151_td
13

@performance_1152_td
0

@performance_1153_td
1

@performance_1154_td
BenchA: Init

@performance_1155_td
ms

@performance_1156_td
2781

@performance_1157_td
2954

@performance_1158_td
7828

@performance_1159_td
4875

@performance_1160_td
3859

@performance_1161_td
BenchA: Transactions

@performance_1162_td
ms

@performance_1163_td
13015

@performance_1164_td
11718

@performance_1165_td
30031

@performance_1166_td
17672

@performance_1167_td
13187

@performance_1168_td
BenchA: Memory Usage

@performance_1169_td
MB

@performance_1170_td
9

@performance_1171_td
17

@performance_1172_td
10

@performance_1173_td
1

@performance_1174_td
1

@performance_1175_td
BenchB: Init

@performance_1176_td
ms

@performance_1177_td
12000

@performance_1178_td
13047

@performance_1179_td
30562

@performance_1180_td
20687

@performance_1181_td
15328

@performance_1182_td
BenchB: Transactions

@performance_1183_td
ms

@performance_1184_td
5375

@performance_1185_td
3688

@performance_1186_td
8063

@performance_1187_td
6250

@performance_1188_td
4594

@performance_1189_td
BenchB: Memory Usage

@performance_1190_td
MB

@performance_1191_td
10

@performance_1192_td
12

@performance_1193_td
8

@performance_1194_td
1

@performance_1195_td
1

@performance_1196_td
BenchC: Init

@performance_1197_td
ms

@performance_1198_td
2390

@performance_1199_td
1875

@performance_1200_td
7015

@performance_1201_td
2515

@performance_1202_td
4062

@performance_1203_td
BenchC: Transactions

@performance_1204_td
ms

@performance_1205_td
11391

@performance_1206_td
77922

@performance_1207_td
23766

@performance_1208_td
13203

@performance_1209_td
8141

@performance_1210_td
BenchC: Memory Usage

@performance_1211_td
MB

@performance_1212_td
11

@performance_1213_td
18

@performance_1214_td
15

@performance_1215_td
1

@performance_1216_td
1

@performance_1217_td
Executed statements

@performance_1218_td
#

@performance_1219_td
594255

@performance_1220_td
594255

@performance_1221_td
594255

@performance_1222_td
594255

@performance_1223_td
594255

@performance_1224_td
Total time

@performance_1225_td
ms

@performance_1226_td
61530

@performance_1227_td
127250

@performance_1228_td
170108

@performance_1229_td
90545

@performance_1230_td
69343

@performance_1231_td
Statements per second

@performance_1232_td
#

@performance_1233_td
9657

@performance_1234_td
4669

@performance_1235_td
3493

@performance_1236_td
6563

@performance_1237_td
8569

@performance_1238_h3
Benchmark Results and Comments

@performance_1239_h4
H2

@performance_1240_p
Version 1.0.78 (2008-08-28) was used for the test. For simpler operations, the performance of H2 is about the same as for HSQLDB. For more complex queries, the query optimizer is very important. However H2 is not very fast in every case, certain kind of queries may still be slow. One situation where is H2 is slow is large result sets, because they are buffered to disk if more than a certain number of records are returned. The advantage of buffering is, there is no limit on the result set size. The open/close time is almost fixed, because of the file locking protocol: The engine waits some time after opening a database to ensure the database files are not opened by another process.

@performance_1241_h4
HSQLDB

@performance_1242_p
Version 1.8.0.10 was used for the test. Cached tables are used in this test (hsqldb.default_table_type=cached), and the write delay is 1 second (SET WRITE_DELAY 1). HSQLDB is fast when using simple operations. HSQLDB is very slow in the last test (BenchC: Transactions), probably because is has a bad query optimizer. One query where HSQLDB is slow is a two-table join:

@performance_1243_p
The PolePosition benchmark also shows that the query optimizer does not do a very good job for some queries. Another disadvantage of HSQLDB is the slow startup / shutdown time (currently not listed) when using bigger databases. The reason is, a backup of the whole data is made whenever the database is opened or closed.

@performance_1244_h4
Derby

@performance_1245_p
Version 10.4.2.0 was used for the test. Derby is clearly the slowest embedded database in this test. This seems to be a structural problem, because all operations are really slow. It will be hard for the developers of Derby to improve the performance to a reasonable level. A few problems have been identified: Leaving autocommit on is a problem for Derby. If it is switched off during the whole test, the results are about 20% better for Derby. Derby supports a testing mode (system property derby.system.durability=test) where durability is disabled. According to the documentation, this setting should be used for testing only, as the database may not recover after a crash. Enabling this setting improves performance by a factor of 2.6 (embedded mode) or 1.4 (server mode). Even if enabled, Derby is still less than half as fast as H2 in default mode.

@performance_1246_h4
PostgreSQL

@performance_1247_p
Version 8.3.4 was used for the test. The following options where changed in postgresql.conf: fsync = off, commit_delay = 1000. PostgreSQL is run in server mode. It looks like the base performance is slower than MySQL, the reason could be the network layer. The memory usage number is incorrect, because only the memory usage of the JDBC driver is measured.

@performance_1248_h4
MySQL

@performance_1249_p
Version 5.0.67 was used for the test. MySQL was run with the InnoDB backend. The setting innodb_flush_log_at_trx_commit (found in the my.ini file) was set to 0. Otherwise (and by default), MySQL is really slow (around 140 statements per second in this test) because it tries to flush the data to disk for each commit. For small transactions (when autocommit is on) this is really slow. But many use cases use small or relatively small transactions. Too bad this setting is not listed in the configuration wizard, and it always overwritten when using the wizard. You need to change this setting manually in the file my.ini, and then restart the service. The memory usage number is incorrect, because only the memory usage of the JDBC driver is measured.

@performance_1250_h4
Firebird

@performance_1251_p
Firebird 1.5 (default installation) was tested, but the results are not published currently. It is possible to run the performance test with the Firebird database, and any information on how to configure Firebird for higher performance are welcome.

@performance_1252_h4
Why Oracle / MS SQL Server / DB2 are Not Listed

@performance_1253_p
The license of these databases does not allow to publish benchmark results. This doesn't mean that they are fast. They are in fact quite slow, and need a lot of memory. But you will need to test this yourself. SQLite was not tested because the JDBC driver doesn't support transactions.

@performance_1254_h3
About this Benchmark

@performance_1255_h4
How to Run

@performance_1256_p
This test was executed as follows:

@performance_1257_h4
Separate Process per Database

@performance_1258_p
For each database, a new process is started, to ensure the previous test does not impact the current test.

@performance_1259_h4
Number of Connections

@performance_1260_p
This is mostly a single-connection benchmark. BenchB uses multiple connections; the other tests use one connection.

@performance_1261_h4
Real-World Tests

@performance_1262_p
Good benchmarks emulate real-world use cases. This benchmark includes 3 test cases: A simple test case with one table and many small updates / deletes. BenchA is similar to the TPC-A test, but single connection / single threaded (see also: www.tpc.org). BenchB is similar to the TPC-B test, using multiple connections (one thread per connection). BenchC is similar to the TPC-C test, but single connection / single threaded.

@performance_1263_h4
Comparing Embedded with Server Databases

@performance_1264_p
This is mainly a benchmark for embedded databases (where the application runs in the same virtual machine as the database engine). However MySQL and PostgreSQL are not Java databases and cannot be embedded into a Java application. For the Java databases, both embedded and server modes are tested.

@performance_1265_h4
Test Platform

@performance_1266_p
This test is run on Windows XP with the virus scanner switched off. The VM used is Sun JDK 1.5.

@performance_1267_h4
Multiple Runs

@performance_1268_p
When a Java benchmark is run first, the code is not fully compiled and therefore runs slower than when running multiple times. A benchmark should always run the same test multiple times and ignore the first run(s). This benchmark runs three times, but only the last run is measured.

@performance_1269_h4
Memory Usage

@performance_1270_p
It is not enough to measure the time taken, the memory usage is important as well. Performance can be improved by using a bigger cache, but the amount of memory is limited. HSQLDB tables are kept fully in memory by default; this benchmark uses 'disk based' tables for all databases. Unfortunately, it is not so easy to calculate the memory usage of PostgreSQL and MySQL, because they run in a different process than the test. This benchmark currently does not print memory usage of those databases.

@performance_1271_h4
Delayed Operations

@performance_1272_p
Some databases delay some operations (for example flushing the buffers) until after the benchmark is run. This benchmark waits between each database tested, and each database runs in a different process (sequentially).

@performance_1273_h4
Transaction Commit / Durability

@performance_1274_p
Durability means transaction committed to the database will not be lost. Some databases (for example MySQL) try to enforce this by default by calling fsync() to flush the buffers, but most hard drives don't actually flush all data. Calling fsync() slows down transaction commit a lot, but doesn't always make data durable. When comparing the results, it is important to think about the effect. Many database suggest to 'batch' operations when possible. This benchmark switches off autocommit when loading the data, and calls commit after each 1000 inserts. However many applications need 'short' transactions at runtime (a commit after each update). This benchmark commits after each update / delete in the simple benchmark, and after each business transaction in the other benchmarks. For databases that support delayed commits, a delay of one second is used.

@performance_1275_h4
Using Prepared Statements

@performance_1276_p
Wherever possible, the test cases use prepared statements.

@performance_1277_h4
Currently Not Tested: Startup Time

@performance_1278_p
The startup time of a database engine is important as well for embedded use. This time is not measured currently. Also, not tested is the time used to create a database and open an existing database. Here, one (wrapper) connection is opened at the start, and for each step a new connection is opened and then closed.

@performance_1279_h2
PolePosition Benchmark

@performance_1280_p
The PolePosition is an open source benchmark. The algorithms are all quite simple. It was developed / sponsored by db4o.

@performance_1281_th
Test Case

@performance_1282_th
Unit

@performance_1283_th
H2

@performance_1284_th
HSQLDB

@performance_1285_th
MySQL

@performance_1286_td
Melbourne write

@performance_1287_td
ms

@performance_1288_td
369

@performance_1289_td
249

@performance_1290_td
2022

@performance_1291_td
Melbourne read

@performance_1292_td
ms

@performance_1293_td
47

@performance_1294_td
49

@performance_1295_td
93

@performance_1296_td
Melbourne read_hot

@performance_1297_td
ms

@performance_1298_td
24

@performance_1299_td
43

@performance_1300_td
95

@performance_1301_td
Melbourne delete

@performance_1302_td
ms

@performance_1303_td
147

@performance_1304_td
133

@performance_1305_td
176

@performance_1306_td
Sepang write

@performance_1307_td
ms

@performance_1308_td
965

@performance_1309_td
1201

@performance_1310_td
3213

@performance_1311_td
Sepang read

@performance_1312_td
ms

@performance_1313_td
765

@performance_1314_td
948

@performance_1315_td
3455

@performance_1316_td
Sepang read_hot

@performance_1317_td
ms

@performance_1318_td
789

@performance_1319_td
859

@performance_1320_td
3563

@performance_1321_td
Sepang delete

@performance_1322_td
ms

@performance_1323_td
1384

@performance_1324_td
1596

@performance_1325_td
6214

@performance_1326_td
Bahrain write

@performance_1327_td
ms

@performance_1328_td
1186

@performance_1329_td
1387

@performance_1330_td
6904

@performance_1331_td
Bahrain query_indexed_string

@performance_1332_td
ms

@performance_1333_td
336

@performance_1334_td
170

@performance_1335_td
693

@performance_1336_td
Bahrain query_string

@performance_1337_td
ms

@performance_1338_td
18064

@performance_1339_td
39703

@performance_1340_td
41243

@performance_1341_td
Bahrain query_indexed_int

@performance_1342_td
ms

@performance_1343_td
104

@performance_1344_td
134

@performance_1345_td
678

@performance_1346_td
Bahrain update

@performance_1347_td
ms

@performance_1348_td
191

@performance_1349_td
87

@performance_1350_td
159

@performance_1351_td
Bahrain delete

@performance_1352_td
ms

@performance_1353_td
1215

@performance_1354_td
729

@performance_1355_td
6812

@performance_1356_td
Imola retrieve

@performance_1357_td
ms

@performance_1358_td
198

@performance_1359_td
194

@performance_1360_td
4036

@performance_1361_td
Barcelona write

@performance_1362_td
ms

@performance_1363_td
413

@performance_1364_td
832

@performance_1365_td
3191

@performance_1366_td
Barcelona read

@performance_1367_td
ms

@performance_1368_td
119

@performance_1369_td
160

@performance_1370_td
1177

@performance_1371_td
Barcelona query

@performance_1372_td
ms

@performance_1373_td
20

@performance_1374_td
5169

@performance_1375_td
101

@performance_1376_td
Barcelona delete

@performance_1377_td
ms

@performance_1378_td
388

@performance_1379_td
319

@performance_1380_td
3287

@performance_1381_td
Total

@performance_1382_td
ms

@performance_1383_td
26724

@performance_1384_td
53962

@performance_1385_td
87112

@performance_1386_p
There are a few problems with the PolePosition test:

@performance_1387_li
HSQLDB uses in-memory tables by default while H2 uses persistent tables. The HSQLDB version included in PolePosition does not support changing this, so you need to replace poleposition-0.20/lib/hsqldb.jar with a newer version (for example hsqldb-1.8.0.7.jar), and then use the setting hsqldb.connecturl=jdbc:hsqldb:file:data/hsqldb/dbbench2;hsqldb.default_table_type=cached;sql.enforce_size=true in Jdbc.properties.

@performance_1388_li
HSQLDB keeps the database open between tests, while H2 closes the database (losing all the cache). To change that, use the database URL jdbc:h2:file:data/h2/dbbench;DB_CLOSE_DELAY=-1

@performance_1389_li
The amount of cache memory is quite important, specially for the PolePosition test. Unfortunately, the PolePosition test does not take this into account.

@performance_1390_h2
Application Profiling

@performance_1391_h3
Analyze First

@performance_1392_p
Before trying to optimize performance, it is important to understand where the problem is (what part of the application is slow). Blind optimization or optimization based on guesses should be avoided, because usually it is not an efficient strategy. There are various ways to analyze an application. Sometimes two implementations can be compared using System.currentTimeMillis(). But this does not work for complex applications with many modules, and for memory problems.

@performance_1393_p
A good tool to measure both memory usage and performance is the <a href="http://www.yourkit.com">YourKit Java Profiler</a> .

@performance_1394_p
A simple way to profile an application is to use the built-in profiling tool of java. Example:

@performance_1395_p
Unfortunately, it is only possible to profile the application from start to end. Another solution is to create a number of full thread dumps. To do that, first run <code>jps -l</code> to get the process id, and then run <code>jstack &lt;pid&gt;</code> or <code>kill -QUIT &lt;pid&gt;</code> (Linux) or press Ctrl+C (Windows).

@performance_1396_h2
Database Profiling

@performance_1397_p
The ConvertTraceFile tool generates SQL statement statistics at the end of the SQL script file. The format used is similar to the profiling data generated when using java -Xrunhprof. As an example, execute the the following script using the H2 Console:

@performance_1398_p
Now convert the .trace.db file using the ConvertTraceFile tool:

@performance_1399_p
The generated file <code>test.sql</code> will contain the SQL statements as well as the following profiling data (results vary):

@performance_1400_h2
Database Performance Tuning

@performance_1401_h3
Virus Scanners

@performance_1402_p
Some virus scanners scan files every time they are accessed. It is very important for performance that database files are not scanned for viruses. The database engine does never interprets the data stored in the files as programs, that means even if somebody would store a virus in a database file, this would be harmless (when the virus does not run, it cannot spread). Some virus scanners allow to exclude files by suffix. Make sure files ending with .db are not scanned.

@performance_1403_h3
Using the Trace Options

@performance_1404_p
If the main performance hot spots are in the database engine, in many cases the performance can be optimized by creating additional indexes, or changing the schema. Sometimes the application does not directly generate the SQL statements, for example if an O/R mapping tool is used. To view the SQL statements and JDBC API calls, you can use the trace options. For more information, see <a href="features.html#trace_options">Using the Trace Options</a> .

@performance_1405_h3
Index Usage

@performance_1406_p
This database uses indexes to improve the performance of SELECT, UPDATE and DELETE statements. If a column is used in the WHERE clause of a query, and if an index exists on this column, then the index can be used. Multi-column indexes are used if all or the first columns of the index are used. Both equality lookup and range scans are supported. Indexes are used to order result sets, but only if the condition uses the same index or no index at all. The results are sorted in memory if required. Indexes are created automatically for primary key and unique constraints. Indexes are also created for foreign key constraints, if required. For other columns, indexes need to be created manually using the CREATE INDEX statement.

@performance_1407_h3
Optimizer

@performance_1408_p
This database uses a cost based optimizer. For simple and queries and queries with medium complexity (less than 7 tables in the join), the expected cost (running time) of all possible plans is calculated, and the plan with the lowest cost is used. For more complex queries, the algorithm first tries all possible combinations for the first few tables, and the remaining tables added using a greedy algorithm (this works well for most joins). Afterwards a genetic algorithm is used to test at most 2000 distinct plans. Only left-deep plans are evaluated.

@performance_1409_h3
Expression Optimization

@performance_1410_p
After the statement is parsed, all expressions are simplified automatically if possible. Operations are evaluated only once if all parameters are constant. Functions are also optimized, but only if the function is constant (always returns the same result for the same parameter values). If the WHERE clause is always false, then the table is not accessed at all.

@performance_1411_h3
COUNT(*) Optimization

@performance_1412_p
If the query only counts all rows of a table, then the data is not accessed. However, this is only possible if no WHERE clause is used, that means it only works for queries of the form SELECT COUNT(*) FROM table.

@performance_1413_h3
Updating Optimizer Statistics / Column Selectivity

@performance_1414_p
When executing a query, at most one index per joined table can be used. If the same table is joined multiple times, for each join only one index is used. Example: for the query SELECT * FROM TEST T1, TEST T2 WHERE T1.NAME='A' AND T2.ID=T1.ID, two index can be used, in this case the index on NAME for T1 and the index on ID for T2.

@performance_1415_p
If a table has multiple indexes, sometimes more than one index could be used. Example: if there is a table TEST(ID, NAME, FIRSTNAME) and an index on each column, then two indexes could be used for the query SELECT * FROM TEST WHERE NAME='A' AND FIRSTNAME='B', the index on NAME or the index on FIRSTNAME. It is not possible to use both indexes at the same time. Which index is used depends on the selectivity of the column. The selectivity describes the 'uniqueness' of values in a column. A selectivity of 100 means each value appears only once, and a selectivity of 1 means the same value appears in many or most rows. For the query above, the index on NAME should be used if the table contains more distinct names than first names.

@performance_1416_p
The SQL statement ANALYZE can be used to automatically estimate the selectivity of the columns in the tables. This command should be run from time to time to improve the query plans generated by the optimizer.

@performance_1417_h3
Optimization Examples

@performance_1418_p
See <code>src/test/org/h2/samples/optimizations.sql</code> for a few examples of queries that benefit from special optimizations built into the database.

@performance_1419_h3
Cache Size and Type

@performance_1420_p
By default the cache size of H2 is quite small. Consider using a larger cache size, or enable the second level soft reference cache. See also <a href="features.html#cache_settings">Cache Settings</a> .

@quickstart_1000_h1
Quickstart

@quickstart_1001_a
Embedding H2 in an Application

@quickstart_1002_a
The H2 Console Application

@quickstart_1003_h2
Embedding H2 in an Application

@quickstart_1004_p
This database can be used in embedded mode, or in server mode. To use it in embedded mode, you need to:

@quickstart_1005_li
Add the <code>h2*.jar</code> to the classpath (H2 does not have any dependencies)

@quickstart_1006_li
Use the JDBC driver class: <code>org.h2.Driver</code>

@quickstart_1007_li
The database URL <code>jdbc:h2:~/test</code> opens the database 'test' in your user home directory

@quickstart_1008_li
A new database is automatically created

@quickstart_1009_h2
The H2 Console Application

@quickstart_1010_p
The Console lets you access a SQL database using a browser interface.

@quickstart_1011_p
If you don't have Windows XP, or if something does not work as expected, please see the detailed description in the <a href="tutorial.html">Tutorial</a> .

@quickstart_1012_h3
Step-by-Step

@quickstart_1013_h4
Installation

@quickstart_1014_p
Install the software using the Windows Installer (if you did not yet do that).

@quickstart_1015_h4
Start the Console

@quickstart_1016_p
Click [Start], [All Programs], [H2], and [H2 Console (Command Line)]:

@quickstart_1017_p
A new console window appears:

@quickstart_1018_p
Also, a new browser page should open with the URL <a href="http://localhost:8082">http://localhost:8082</a> . You may get a security warning from the firewall. If you don't want other computers in the network to access the database on your machine, you can let the firewall block these connections. Only local connections are required at this time.

@quickstart_1019_h4
Login

@quickstart_1020_p
Select [Generic H2] and click [Connect]:

@quickstart_1021_p
You are now logged in.

@quickstart_1022_h4
Sample

@quickstart_1023_p
Click on the [Sample SQL Script]:

@quickstart_1024_p
The SQL commands appear in the command area.

@quickstart_1025_h4
Execute

@quickstart_1026_p
Click [Run]

@quickstart_1027_p
On the left side, a new entry TEST is added below the database icon. The operations and results of the statements are shown below the script.

@quickstart_1028_h4
Disconnect

@quickstart_1029_p
Click on [Disconnect]:

@quickstart_1030_p
to close the connection.

@quickstart_1031_h4
End

@quickstart_1032_p
Close the console window. For more information, see the <a href="tutorial.html">Tutorial</a> .

@roadmap_1000_h1
Roadmap

@roadmap_1001_p
New (feature) requests will usually be added at the very end of the list. The priority is increased for important and popular requests. Of course, patches are always welcome, but are not always applied as is. See also <a href="build.html#providing_patches">Providing Patches</a> .

@roadmap_1002_h2
Priority 1

@roadmap_1003_li
Bugfixes

@roadmap_1004_li
Page store: new storage mechanism

@roadmap_1005_li
[Requires page store] Support large updates (use the transaction log to undo).

@roadmap_1006_li
[Requires page store] Shutdown compact

@roadmap_1007_li
Optimize IN(...) for SELECT, DELETE, and UPDATE.

@roadmap_1008_li
More tests with MULTI_THREADED=1

@roadmap_1009_li
RECOVER=1 should automatically recover, =2 should run the recovery tool if required

@roadmap_1010_li
Optimization: result set caching (like MySQL)

@roadmap_1011_li
Server side cursors

@roadmap_1012_h2
Priority 2

@roadmap_1013_li
Improve test code coverage

@roadmap_1014_li
Procedural language / script language (Java, Javascript)

@roadmap_1015_li
Fulltext search: support streaming CLOB data.

@roadmap_1016_li
Optimize .. OR .. to IN(..) or UNION if the cost is lower

@roadmap_1017_li
Enable warning for 'Local variable declaration hides another field or variable'.

@roadmap_1018_li
Test multi-threaded in-memory db access

@roadmap_1019_li
MVCC: Select for update should only lock the selected rows.

@roadmap_1020_li
Option to shutdown all the running servers (on the same VM).

@roadmap_1021_li
Optimize ID=? OR ID=?: convert to IN(...)

@roadmap_1022_li
Index organized tables CREATE TABLE...(...) ORGANIZATION INDEX (store in data file) (probably file format changes are required for rowId)

@roadmap_1023_li
Better space re-use in the files after deleting data: shrink the data file without closing the database (if the end of the file is empty)

@roadmap_1024_li
Implement INSTEAD OF trigger (for views, tables, metadata tables).

@roadmap_1025_li
Triggers for metadata tables; use for PostgreSQL catalog

@roadmap_1026_li
Support triggers for INFORMATION_SCHEMA tables (to better support PostgreSQL catalog: rebuild after creating new tables)

@roadmap_1027_li
Full outer joins

@roadmap_1028_li
Maven: deploy / upload h2..-sources.jar and javadocs as well.

@roadmap_1029_li
Support trigger on the tables information_schema.tables and ...columns

@roadmap_1030_li
Test very large databases and LOBs (up to 256 GB)

@roadmap_1031_li
Support hints for the optimizer (which index to use, enforce the join order).

@roadmap_1032_li
Change LOB mechanism (less files, keep index of lob files, point to files and row, delete unused files earlier, maybe bundle files into a tar file)

@roadmap_1033_li
Clustering: recovery needs to becomes fully automatic. Global write lock feature.

@roadmap_1034_li
Support mixed clustering mode (one embedded, the other server mode)

@roadmap_1035_li
Sequence: add features [NO] MINVALUE, MAXVALUE, CYCLE

@roadmap_1036_li
Deferred integrity checking (DEFERRABLE INITIALLY DEFERRED)

@roadmap_1037_li
Groovy Stored Procedures (http://groovy.codehaus.org/Groovy+SQL)

@roadmap_1038_li
Add a migration guide (list differences between databases)

@roadmap_1039_li
Migrate database tool (also from other database engines)

@roadmap_1040_li
Optimization: automatic index creation suggestion using the trace file?

@roadmap_1041_li
Compression performance: don't allocate buffers, compress / expand in to out buffer

@roadmap_1042_li
Rebuild index functionality to shrink index size and improve performance

@roadmap_1043_li
Don't use deleteOnExit (bug 4513817: File.deleteOnExit consumes memory)

@roadmap_1044_li
Console: add accesskey to most important commands (A, AREA, BUTTON, INPUT, LABEL, LEGEND, TEXTAREA)

@roadmap_1045_li
Support nested outer joins (see todo.txt).

@roadmap_1046_li
Don't write stack traces for common exceptions like duplicate key to the log by default (exclude list)

@roadmap_1047_li
Test performance again with SQL Server, Oracle, DB2

@roadmap_1048_li
Test with dbmonster (http://dbmonster.kernelpanic.pl/)

@roadmap_1049_li
Test with dbcopy (http://dbcopyplugin.sourceforge.net)

@roadmap_1050_li
Test with Spatial DB in a box / JTS: http://www.opengeospatial.org/standards/sfs - OpenGIS Implementation Specification

@roadmap_1051_li
Write more tests and documentation for MVCC (Multi Version Concurrency Control)

@roadmap_1052_li
Find a tool to view large text file (larger than 100 MB), with find, page up and down (like less), truncate before / after

@roadmap_1053_li
Implement, test, document XAConnection and so on

@roadmap_1054_li
Pluggable data type (for compression, validation, conversion, encryption)

@roadmap_1055_li
CHECK: find out what makes CHECK=TRUE slow, move to CHECK2

@roadmap_1056_li
Improve recovery: improve code for log recovery problems (less try/catch)

@roadmap_1057_li
Index usage for (ID, NAME)=(1, 'Hi'); document

@roadmap_1058_li
Suggestion: include Jetty as Servlet Container (like LAMP)

@roadmap_1059_li
Trace shipping to server

@roadmap_1060_li
Version check: docs / web console (using Javascript), and maybe in the library (using TCP/IP)

@roadmap_1061_li
Web server classloader: override findResource / getResourceFrom

@roadmap_1062_li
Cost for embedded temporary view is calculated wrong, if result is constant

@roadmap_1063_li
Comparison: pluggable sort order: natural sort

@roadmap_1064_li
Count index range query (count(*) where id between 10 and 20)

@roadmap_1065_li
Eclipse plugin

@roadmap_1066_li
Asynchronous queries to support publish/subscribe: SELECT ... FOR READ WAIT [maxMillisToWait]

@roadmap_1067_li
Fulltext search Lucene: analyzer configuration.

@roadmap_1068_li
Fulltext search (native): reader / tokenizer / filter.

@roadmap_1069_li
Linked schema using CSV files: one schema for a directory of files; support indexes for CSV files

@roadmap_1070_li
iReport to support H2

@roadmap_1071_li
Implement missing JDBC API (CallableStatement,...)

@roadmap_1072_li
Compression of the cache

@roadmap_1073_li
Include SMPT (mail) server (at least client) (alert on cluster failure, low disk space,...)

@roadmap_1074_li
Drop with restrict (currently cascade is the default)

@roadmap_1075_li
JSON parser and functions

@roadmap_1076_li
Automatic collection of statistics (auto ANALYZE)

@roadmap_1077_li
Server: client ping from time to time (to avoid timeout - is timeout a problem?)

@roadmap_1078_li
Copy database: Tool with config GUI and batch mode, extensible (example: compare)

@roadmap_1079_li
Document, implement tool for long running transactions using user-defined compensation statements.

@roadmap_1080_li
Support SET TABLE DUAL READONLY

@roadmap_1081_li
GCJ: what is the state now?

@roadmap_1082_li
Events for: Database Startup, Connections, Login attempts, Disconnections, Prepare (after parsing), Web Server (see http://docs.openlinksw.com/virtuoso/fn_dbev_startup.html)

@roadmap_1083_li
Optimization: Log compression

@roadmap_1084_li
Support standard INFORMATION_SCHEMA tables, as defined in http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt; specially KEY_COLUMN_USAGE (http://dev.mysql.com/doc/refman/5.0/en/information-schema.html, http://www.xcdsql.org/Misc/INFORMATION_SCHEMA%20With%20Rolenames.gif)

@roadmap_1085_li
Compatibility: in MySQL, HSQLDB, /0.0 is NULL; in PostgreSQL, Derby: Division by zero

@roadmap_1086_li
Functional tables should accept parameters from other tables (see FunctionMultiReturn) SELECT * FROM TEST T, P2C(T.A, T.R)

@roadmap_1087_li
Custom class loader to reload functions on demand

@roadmap_1088_li
Test http://mysql-je.sourceforge.net/

@roadmap_1089_li
Close all files when closing the database (including LOB files that are open on the client side)

@roadmap_1090_li
EXE file: maybe use http://jsmooth.sourceforge.net

@roadmap_1091_li
Performance: Automatically build in-memory indexes if the whole table is in memory

@roadmap_1092_li
H2 Console: The webclient could support more features like phpMyAdmin.

@roadmap_1093_li
Use Janino to convert Java to C++

@roadmap_1094_li
The HELP information schema can be directly exposed in the Console

@roadmap_1095_li
Maybe use the 0x1234 notation for binary fields, see MS SQL Server

@roadmap_1096_li
Support Oracle CONNECT BY in some way: http://www.adp-gmbh.ch/ora/sql/connect_by.html, http://philip.greenspun.com/sql/trees.html

@roadmap_1097_li
SQL Server 2005, Oracle: Support COUNT(*) OVER(). See http://www.orafusion.com/art_anlytc.htm

@roadmap_1098_li
RANK() and DENSE_RANK(), Partition using OVER()

@roadmap_1099_li
SQL 2003 (http://www.wiscorp.com/sql_2003_standard.zip)

@roadmap_1100_li
Version column (number/sequence and timestamp based)

@roadmap_1101_li
Optimize getGeneratedKey: send last identity after each execute (server).

@roadmap_1102_li
Test and document UPDATE TEST SET (ID, NAME) = (SELECT ID*10, NAME || '!' FROM TEST T WHERE T.ID=TEST.ID);

@roadmap_1103_li
Max memory rows / max undo log size: use block count / row size not row count

@roadmap_1104_li
Support 123L syntax as in Java; example: SELECT (2000000000*2)

@roadmap_1105_li
Implement point-in-time recovery

@roadmap_1106_li
LIKE: improved version for larger texts (currently using naive search)

@roadmap_1107_li
Automatically convert to the next 'higher' data type whenever there is an overflow.

@roadmap_1108_li
Throw an exception when the application calls getInt on a Long (optional)

@roadmap_1109_li
Default date format for input and output (local date constants)

@roadmap_1110_li
Support custom Collators

@roadmap_1111_li
Document ROWNUM usage for reports: SELECT ROWNUM, * FROM (subquery)

@roadmap_1112_li
Clustering: Reads should be randomly distributed or to a designated database on RAM

@roadmap_1113_li
Clustering: When a database is back alive, automatically synchronize with the master

@roadmap_1114_li
Standalone tool to get relevant system properties and add it to the trace output.

@roadmap_1115_li
Support 'call proc(1=value)' (PostgreSQL, Oracle)

@roadmap_1116_li
JAMon (proxy jdbc driver)

@roadmap_1117_li
Console: Improve editing data (Tab, Shift-Tab, Enter, Up, Down, Shift+Del?)

@roadmap_1118_li
Console: Autocomplete Ctrl+Space inserts template

@roadmap_1119_li
Simplify translation ('Donate a translation')

@roadmap_1120_li
Option to encrypt .trace.db file

@roadmap_1121_li
Write Behind Cache on SATA leads to data corruption See also http://sr5tech.com/write_back_cache_experiments.htm and http://www.jasonbrome.com/blog/archives/2004/04/03/writecache_enabled.html

@roadmap_1122_li
Functions with unknown return or parameter data types: serialize / deserialize

@roadmap_1123_li
Test if idle TCP connections are closed, and how to disable that

@roadmap_1124_li
Try using a factory for Row, Value[] (faster?), http://javolution.org/, alternative ObjectArray / IntArray

@roadmap_1125_li
Auto-Update feature for database, .jar file

@roadmap_1126_li
ResultSet SimpleResultSet.readFromURL(String url): id varchar, state varchar, released timestamp

@roadmap_1127_li
ROW_NUMBER (not the same as ROWNUM)

@roadmap_1128_li
Partial indexing (see PostgreSQL)

@roadmap_1129_li
The build should fail if the test fails

@roadmap_1130_li
Add GUI to build a custom version (embedded, fulltext,...) using build flags

@roadmap_1131_li
http://rubyforge.org/projects/hypersonic/

@roadmap_1132_li
Add comparator (x === y) : (x = y or (x is null and y is null))

@roadmap_1133_li
Try to create trace file even for read only databases

@roadmap_1134_li
Add a sample application that runs the H2 unit test and writes the result to a file (so it can be included in the user app)

@roadmap_1135_li
Count on a column that can not be null could be optimized to COUNT(*)

@roadmap_1136_li
Table order: ALTER TABLE TEST ORDER BY NAME DESC (MySQL compatibility)

@roadmap_1137_li
Backup tool should work with other databases as well

@roadmap_1138_li
Console: -ifExists doesn't work for the console. Add a flag to disable other dbs

@roadmap_1139_li
Performance: Update in-place

@roadmap_1140_li
Check if 'FSUTIL behavior set disablelastaccess 1' improves the performance (fsutil behavior query disablelastaccess)

@roadmap_1141_li
Java static code analysis: http://pmd.sourceforge.net/

@roadmap_1142_li
Java static code analysis: http://www.eclipse.org/tptp/

@roadmap_1143_li
Compatibility for CREATE SCHEMA AUTHORIZATION

@roadmap_1144_li
Implement Clob / Blob truncate and the remaining functionality

@roadmap_1145_li
Maybe close LOBs after closing connection

@roadmap_1146_li
Tree join functionality

@roadmap_1147_li
Support alter table add column if table has views defined

@roadmap_1148_li
Add multiple columns at the same time with ALTER TABLE .. ADD .. ADD ..

@roadmap_1149_li
Add H2 to Gem (Ruby install system)

@roadmap_1150_li
API for functions / user tables

@roadmap_1151_li
Order conditions inside AND / OR to optimize the performance

@roadmap_1152_li
Support linked JCR tables

@roadmap_1153_li
Make sure H2 is supported by Execute Query: http://executequery.org/

@roadmap_1154_li
Read InputStream when executing, as late as possible (maybe only embedded mode). Problem with re-execute.

@roadmap_1155_li
Native fulltext search: min word length; store word positions

@roadmap_1156_li
Store dates in local time zone (portability of database files)

@roadmap_1157_li
Recursive Queries (see details)

@roadmap_1158_li
Add an option to the SCRIPT command to generate only portable / standard SQL

@roadmap_1159_li
Test Dezign for Databases (http://www.datanamic.com)

@roadmap_1160_li
Fast library for parsing / formatting: http://javolution.org/

@roadmap_1161_li
Updatable Views (simple cases first)

@roadmap_1162_li
Improve create index performance

@roadmap_1163_li
Implement more JDBC 4.0 features

@roadmap_1164_li
Support TRANSFORM / PIVOT as in MS Access

@roadmap_1165_li
SELECT * FROM (VALUES (...), (...), ....) AS alias(f1, ...)

@roadmap_1166_li
Support updatable views with join on primary keys (to extend a table)

@roadmap_1167_li
Public interface for functions (not public static)

@roadmap_1168_li
Autocomplete: if I type the name of a table that does not exist (should say: syntax not supported)

@roadmap_1169_li
Document FTP server, including -ftpTask option to execute / kill remote processes

@roadmap_1170_li
Eliminate undo log records if stored on disk (just one pointer per block, not per record)

@roadmap_1171_li
Feature matrix like in <a href="http://www.inetsoftware.de/products/jdbc/mssql/features/default.asp">i-net software</a> .

@roadmap_1172_li
Updatable result set on table without primary key or unique index

@roadmap_1173_li
Use LinkedList instead of ArrayList where applicable

@roadmap_1174_li
Optimizer: use an index for IS NULL and IS NOT NULL (including linked tables).  ID IS NOT NULL could be converted to ID >= Integer.MIN_VALUE.

@roadmap_1175_li
Support % operator (modulo)

@roadmap_1176_li
Support 1+'2'=3, '1'+'2'='12' (MS SQL Server compatibility)

@roadmap_1177_li
Support nested transactions

@roadmap_1178_li
Add a benchmark for big databases, and one for many users

@roadmap_1179_li
Compression in the result set (repeating values in the same column) over TCP/IP

@roadmap_1180_li
Support curtimestamp (like curtime, curdate)

@roadmap_1181_li
Support ANALYZE {TABLE|INDEX} tableName COMPUTE|ESTIMATE|DELETE STATISTICS ptnOption options

@roadmap_1182_li
Support Sequoia (Continuent.org)

@roadmap_1183_li
Dynamic length numbers / special methods for DataPage.writeByte / writeShort / Ronni Nielsen

@roadmap_1184_li
Pluggable ThreadPool, (AvalonDB / deebee / Paul Hammant)

@roadmap_1185_li
Release locks (shared or exclusive) on demand

@roadmap_1186_li
Support OUTER UNION

@roadmap_1187_li
Support parameterized views (similar to CSVREAD, but using just SQL for the definition)

@roadmap_1188_li
A way (JDBC driver) to map an URL (jdbc:h2map:c1) to a connection object

@roadmap_1189_li
Option for SCRIPT to only process one or a set of tables, and append to a file

@roadmap_1190_li
Support linked tables to the current database

@roadmap_1191_li
Support dynamic linked schema (automatically adding/updating/removing tables)

@roadmap_1192_li
Compatibility with Derby: VALUES(1), (2); SELECT * FROM (VALUES (1), (2)) AS myTable(c1)

@roadmap_1193_li
Compatibility: # is the start of a single line comment (MySQL) but date quote (Access). Mode specific

@roadmap_1194_li
Run benchmarks with JDK 1.5, JDK 1.6, java -server

@roadmap_1195_li
Optimizations: Faster hash function for strings, byte arrays

@roadmap_1196_li
DatabaseEventListener: callback for all operations (including expected time, RUNSCRIPT) and cancel functionality

@roadmap_1197_li
H2 Console / large result sets: use 'streaming' instead of building the page in-memory

@roadmap_1198_li
Benchmark: add a graph to show how databases scale (performance/database size)

@roadmap_1199_li
Implement a SQLData interface to map your data over to a custom object

@roadmap_1200_li
In the MySQL and PostgreSQL mode, use lower case identifiers by default (DatabaseMetaData.storesLowerCaseIdentifiers = true)

@roadmap_1201_li
Make DDL (Data Definition) operations transactional

@roadmap_1202_li
Allow execution time prepare for SELECT * FROM CSVREAD(?, 'columnNameString')

@roadmap_1203_li
Support multiple directories (on different hard drives) for the same database

@roadmap_1204_li
Server protocol: use challenge response authentication, but client sends hash(user+password) encrypted with response

@roadmap_1205_li
Support EXEC[UTE] (doesn't return a result set, compatible to MS SQL Server)

@roadmap_1206_li
Support native XML data type

@roadmap_1207_li
Support triggers with a string property or option: SpringTrigger, OSGITrigger

@roadmap_1208_li
Clustering: adding a node should be very fast and without interrupting clients (very short lock)

@roadmap_1209_li
Support materialized views (using triggers)

@roadmap_1210_li
Ability to resize the cache array when resizing the cache

@roadmap_1211_li
Time based cache writing (one second after writing the log)

@roadmap_1212_li
Check state of H2 driver for DDLUtils: https://issues.apache.org/jira/browse/DDLUTILS-185

@roadmap_1213_li
Index usage for REGEXP LIKE.

@roadmap_1214_li
Compatibility: add a role DBA (like ADMIN).

@roadmap_1215_li
Better support multiple processors for in-memory databases.

@roadmap_1216_li
Access rights: remember the owner of an object. COMMENT: allow owner of object to change it.

@roadmap_1217_li
Access rights: Finer grained access control (grant access for specific functions)

@roadmap_1218_li
Support N'text'

@roadmap_1219_li
Support SCOPE_IDENTITY() to avoid problems when inserting rows in a trigger

@roadmap_1220_li
Set a connection read only (Connection.setReadOnly)

@roadmap_1221_li
In MySQL mode, for AUTO_INCREMENT columns, don't set the primary key

@roadmap_1222_li
Use JDK 1.4 file locking to create the lock file (but not yet by default); writing a system property to detect concurrent access from the same VM (different classloaders).

@roadmap_1223_li
Support compatibility for jdbc:hsqldb:res:

@roadmap_1224_li
Provide an Java SQL builder with standard and H2 syntax

@roadmap_1225_li
Trace: write OS, file system, JVM,... when opening the database

@roadmap_1226_li
Support indexes for views (probably requires materialized views)

@roadmap_1227_li
Document SET SEARCH_PATH, BEGIN, EXECUTE, parameters

@roadmap_1228_li
Browser: use Desktop.isDesktopSupported and browse when using JDK 1.6

@roadmap_1229_li
Server: use one listener (detect if the request comes from an PG or TCP client)

@roadmap_1230_li
Store dates as 'local'. Existing files use GMT. Use escape syntax for compatibility.

@roadmap_1231_li
Support data type INTERVAL

@roadmap_1232_li
Optimize SELECT MIN(ID), MAX(ID), COUNT(*) FROM TEST WHERE ID BETWEEN 100 AND 200

@roadmap_1233_li
Support Oracle functions: TRUNC, NVL2, TO_CHAR, TO_DATE, TO_NUMBER

@roadmap_1234_li
Sequence: PostgreSQL compatibility (rename, create) (http://www.postgresql.org/docs/8.2/static/sql-altersequence.html)

@roadmap_1235_li
DISTINCT: Support large result sets by sorting on all columns (additionally) and then removing duplicates.

@roadmap_1236_li
File system that writes to two file systems (replicating file system)

@roadmap_1237_li
File system with a background writer thread; test if this is faster

@roadmap_1238_li
FTP access to a database (.csv for a table, a directory for a schema, a file for a lob, a script.sql file).

@roadmap_1239_li
Better document the source code

@roadmap_1240_li
Support select * from dual a left join dual b on b.x=(select max(x) from dual)

@roadmap_1241_li
Optimization: don't lock when the database is read-only

@roadmap_1242_li
Integrate spatial functions from http://geosysin.iict.ch/irstv-trac/wiki/H2spatial/Download

@roadmap_1243_li
Support COSH, SINH, and TANH functions

@roadmap_1244_li
FTP Server: Implement SFTP / FTPS

@roadmap_1245_li
Native search: support "phrase search", wildcard search (* and ?), case-insensitive search, boolean operators, and grouping

@roadmap_1246_li
Improve documentation of access rights

@roadmap_1247_li
Support ENUM data type (see MySQL, PostgreSQL, MS SQL Server, maybe others)

@roadmap_1248_li
Command line option for the H2 Console and TCP configuration (which .h2.server.properties and .h2.keystore to use)

@roadmap_1249_li
Support a schema name for Java functions

@roadmap_1250_li
Remember the user defined data type (domain) of a column

@roadmap_1251_li
Support Jackcess (MS Access databases)

@roadmap_1252_li
Built-in methods to write large objects (BLOB and CLOB): FILE_WRITE('test.txt', 'Hello World')

@roadmap_1253_li
MVCC: support transactionally consistent backups using SCRIPT

@roadmap_1254_li
Improve time to open large databases (see mail 'init time for distributed setup')

@roadmap_1255_li
Move Maven 2 repository from hsql.sf.net to h2database.sf.net

@roadmap_1256_li
Java 1.5 tool: JdbcUtils.closeSilently(s1, s2,...)

@roadmap_1257_li
Javadoc: document design patterns used

@roadmap_1258_li
Does the FTP server has problems with multithreading?

@roadmap_1259_li
Write an article about SQLInjection (h2\src\docsrc\html\images\SQLInjection.txt)

@roadmap_1260_li
Convert SQL-injection-2.txt to html document, include SQLInjection.java sample

@roadmap_1261_li
Improve LOB in directories performance

@roadmap_1262_li
Web site design: http://www.igniterealtime.org/projects/openfire/index.jsp

@roadmap_1263_li
HSQLDB compatibility: Openfire server uses: CREATE SCHEMA PUBLIC AUTHORIZATION DBA;  CREATE USER SA PASSWORD ""; GRANT DBA TO SA; SET SCHEMA PUBLIC

@roadmap_1264_li
Web site: Rename Performance to Comparison [/Compatibility],  move Comparison to Other Database Engines to Comparison,  move Products that Work with H2 to Comparison,  move Performance Tuning to Advanced Topics

@roadmap_1265_li
Support JMX: Create an MBean for each database and server (support JConsole).  See http://thedevcloud.blogspot.com/2008/10/displaying-hsql-database-manager-in.html

@roadmap_1266_li
Translation: use ?? in help.csv

@roadmap_1267_li
Translated .pdf

@roadmap_1268_li
Cluster: hot deploy (adding a node at runtime)

@roadmap_1269_li
MySQL compatibility: update test1 t1, test2 t2 set t1.id = t2.id where t1.id = t2.id;

@roadmap_1270_li
Recovery tool: bad blocks should be converted to INSERT INTO SYSTEM_ERRORS(...), and things should go into the .trace.db file

@roadmap_1271_li
RECOVER=2 to backup the database, run recovery, open the database

@roadmap_1272_li
Recovery should work with encrypted databases

@roadmap_1273_li
Corruption: new error code, add help

@roadmap_1274_li
Space reuse: after init, scan all storages and free those that don't belong to a live database object

@roadmap_1275_li
SysProperties: change everything to H2_...

@roadmap_1276_li
Use FilterIn / FilterOut putStream?

@roadmap_1277_li
Access rights: add missing features (users should be 'owner' of objects; missing rights for sequences; dropping objects)

@roadmap_1278_li
Support NOCACHE table option (Oracle)

@roadmap_1279_li
Index usage for UPDATE ... WHERE .. IN (SELECT...)

@roadmap_1280_li
Add regular javadocs (using the default doclet, but another css) to the homepage.

@roadmap_1281_li
The database should be kept open for a longer time when using the server mode.

@roadmap_1282_li
Javadocs: for each tool, add a copy &amp; paste sample in the class level.

@roadmap_1283_li
Javadocs: add @author tags.

@roadmap_1284_li
Fluent API for tools: Server.createTcpServer().setPort(9081).setPassword(password).start();

@roadmap_1285_li
MySQL compatibility: real SQL statement for DESCRIBE TEST

@roadmap_1286_li
Use a default delay of 1 second before closing a database.

@roadmap_1287_li
Write (log) to system table before adding to internal data structures.

@roadmap_1288_li
Support very large deletes and updates.

@roadmap_1289_li
Doclet (javadocs): constructors are not listed.

@roadmap_1290_li
Support direct lookup for MIN and MAX when using WHERE (see todo.txt / Direct Lookup).

@roadmap_1291_li
Support other array types (String[], double[]) in PreparedStatement.setObject(int, Object);

@roadmap_1292_li
MVCC should not be memory bound (uncommitted data is kept in memory in the delta index; maybe using a regular btree index solves the problem).

@roadmap_1293_li
Oracle compatibility: support NLS_DATE_FORMAT.

@roadmap_1294_li
Support flashback queries as in Oracle.

@roadmap_1295_li
Import / Export of fixed with text files.

@roadmap_1296_li
Support OUT parameters in user-defined procedures.

@roadmap_1297_li
Support getGeneratedKeys to return multiple rows when used with batch updates.  This is supported by MySQL, but not Derby. Both PostgreSQL and HSQLDB don't support getGeneratedKeys.  Also support it when using INSERT ... SELECT.

@roadmap_1298_li
HSQLDB compatibility: automatic data type for SUM if value is the value is too big (by default use the same type as the data).

@roadmap_1299_li
Improve the optimizer to select the right index for special cases: where id between 2 and 4 and booleanColumn

@roadmap_1300_li
Linked tables: make hidden columns available (Oracle: rowid and ora_rowscn columns).

@roadmap_1301_li
Support merge join.

@roadmap_1302_li
H2 Console: in-place autocomplete.

@roadmap_1303_li
Oracle: support DECODE method (convert to CASE WHEN).

@roadmap_1304_li
Support large databases: split LOB (BLOB, CLOB) to multiple directories / disks (similar to tablespaces).

@roadmap_1305_li
Support to assign a primary key index a user defined name.

@roadmap_1306_li
Cluster: Add feature to make sure cluster nodes can not get out of sync (for example by stopping one process).

@roadmap_1307_li
H2 Console: support configuration option for fixed width (monospace) font.

@roadmap_1308_li
Native fulltext search: support analyzers (specially for Chinese, Japanese).

@roadmap_1309_li
Automatically compact databases from time to time (as a background process).

@roadmap_1310_li
Support SCOPE_IDENTITY().

@roadmap_1311_li
Support GRANT SELECT, UPDATE ON *.

@roadmap_1312_li
Test Eclipse DTP.

@roadmap_1313_li
H2 Console: autocomplete: keep the previous setting

@roadmap_1314_li
MySQL, MS SQL Server compatibility: support case sensitive (mixed case) identifiers without quotes.

@roadmap_1315_li
executeBatch: option to stop at the first failed statement.

@roadmap_1316_li
Implement OLAP features as described here: http://www.devx.com/getHelpOn/10MinuteSolution/16573/0/page/5

@roadmap_1317_li
Support Oracle ROWID (unique identifier for each row).

@roadmap_1318_li
Server mode: Improve performance for batch updates.

@roadmap_1319_li
Applets: Support read-only databases in a zip file (accessed as a resource).

@roadmap_1320_li
Long running queries / errors / trace system table.

@roadmap_1321_li
H2 Console should support JaQu directly.

@roadmap_1322_li
H2 Console: support single file upload and directory download (optional).

@roadmap_1323_li
Document FTL_SEARCH, FTL_SEARCH_DATA.

@roadmap_1324_li
Sequences: CURRVAL should be session specific. Compatibility with PostgreSQL.

@roadmap_1325_li
Support DatabaseMetaData.insertsAreDetected: updatable result sets should detect inserts.

@roadmap_1326_li
Auto-server: add option to define the IP address range or list.

@roadmap_1327_li
Index creation only using deterministic functions.

@roadmap_1328_li
Use http://recaptcha.net somehow to secure the Google Group.

@roadmap_1329_li
Support DELETE with TOP or LIMIT. See also: http://dev.mysql.com/doc/refman/5.1/de/delete.html

@roadmap_1330_li
Change the default for NULL || 'x' to return NULL

@roadmap_1331_li
ANALYZE: Use a bloom filter for each indexed column to estimate count of distinct values.

@roadmap_1332_li
ANALYZE: For unique indexes that allow null, count the number of null.

@roadmap_1333_li
AUTO_SERVER: support changing IP addresses (disable a network while the database is open).

@roadmap_1334_li
Avoid using java.util.Calendar internally because it's slow, complicated, and seems to be buggy.

@roadmap_1335_li
Support TRUNCATE .. CASCADE like PostgreSQL.

@roadmap_1336_li
Support opening a database that is in the classpath, maybe using a new file system.

@roadmap_1337_li
Fulltext search: lazy result generation using SimpleRowSource.

@roadmap_1338_li
Support transformation to join for user defined functions, as for IN(SELECT...).

@roadmap_1339_li
Fulltext search: Support alternative syntax: WHERE FTL_CONTAINS(name, 'hello').

@roadmap_1340_li
MySQL compatibility: support REPLACE, see http://dev.mysql.com/doc/refman/5.1/de/replace.html

@roadmap_1341_li
MySQL compatibility: support INSERT INTO table SET column1 = value1, column2 = value2

@roadmap_1342_li
Docs: Add a one line description for each functions and SQL statements at the top (in the link section).

@roadmap_1343_li
Javadoc search: weight for titles should be higher ('random' should list Functions as the best match).

@roadmap_1344_li
Replace information_schema tables with regular tables that are automatically re-built when needed. Use indexes.

@roadmap_1345_li
Support a special trigger on all tables.

@roadmap_1346_li
Delete temporary files or objects using finalize.

@roadmap_1347_li
Oracle compatibility: support calling 0-parameters functions without parenthesis. Make constants obsolete.

@roadmap_1348_li
MySQL, HSQLDB compatibility: support where 'a'=1 (not supported by Derby, PostgreSQL)

@roadmap_1349_li
Allow calling function with no parameters without parenthesis. See http://code.google.com/p/h2database/issues/detail?id=50

@roadmap_1350_li
CSV: currently # is a line comment and can start at any field. Make it optional.

@roadmap_1351_li
Add database creation date and time to the database.

@roadmap_1352_li
Support ASSERTIONS.

@roadmap_1353_li
MySQL compatibility: support comparing 1='a'

@roadmap_1354_li
Support PostgreSQL lock modes: http://www.postgresql.org/docs/8.3/static/explicit-locking.html

@roadmap_1355_li
PostgreSQL compatibility: test DbVisualizer and Squirrel SQL using a new PostgreSQL JDBC driver.

@roadmap_1356_li
RunScript should be able to read from system in (or quite mode for Shell).

@roadmap_1357_li
Natural join: support select x from dual natural join dual.

@roadmap_1358_li
Natural join: somehow support this: select a.x, b.x, x from dual a natural join dual b

@roadmap_1359_li
MySQL compatibility: for auto_increment columns, convert 0 to next value (as when inserting NULL).

@roadmap_1360_li
Functions: support hashcode(value); cryptographic and fast

@roadmap_1361_li
Serialized file lock: support long running queries.

@roadmap_1362_li
Network: use 127.0.0.1 if other addresses don't work.

@roadmap_1363_li
Select for update in mvcc mode: only lock the selected records.

@roadmap_1364_li
Support reading JCR data: one table per node type; query table; cache option

@roadmap_1365_li
OSGi: create a sample application, test, document.

@roadmap_1366_li
help.csv: use complete examples for functions; run as test case.

@roadmap_1367_li
Re-implement PooledConnection; use a lightweight connection object.

@roadmap_1368_li
Doclet: convert tests in javadocs to a java class.

@roadmap_1369_li
Doclet: format fields like methods, but support sorting by name and value.

@roadmap_1370_li
Doclet: shrink the html files.

@roadmap_1371_li
Finer granularity for SLF4J trace - See http://code.google.com/p/h2database/issues/detail?id=62

@roadmap_1372_li
MySQL compatibility: support REPLACE - See http://code.google.com/p/h2database/issues/detail?id=73

@roadmap_1373_li
MySQL compatibility: support SET NAMES 'latin1' - See also http://code.google.com/p/h2database/issues/detail?id=56

@roadmap_1374_li
MySQL compatibility: DELETE .. FROM .. USING - See http://dev.mysql.com/doc/refman/5.0/en/delete.html

@roadmap_1375_li
Allow to scan index backwards starting with a value (to better support ORDER BY DESC).

@roadmap_1376_li
Java Service Wrapper: try http://yajsw.sourceforge.net/

@roadmap_1377_li
Batch parameter for INSERT, UPDATE, and DELETE, and commit after each batch. See also MySQL DELETE.

@roadmap_1378_li
MySQL compatibility: support ALTER TABLE .. MODIFY COLUMN.

@roadmap_1379_li
Use a lazy and auto-close input stream (open resource when reading, close on eof).

@roadmap_1380_li
PostgreSQL compatibility: generate_series.

@roadmap_1381_li
Connection pool: 'reset session' command (delete temp tables, rollback, autocommit true).

@roadmap_1382_li
Improve SQL documentation, see http://www.w3schools.com/sql/

@roadmap_1383_li
MySQL compatibility: DatabaseMetaData.stores*() methods should return the same values. Test with SquirrelSQL.

@roadmap_1384_li
Support table partitioning.

@roadmap_1385_li
MS SQL Server compatibility: support DATEPART syntax.

@roadmap_1386_li
Oracle compatibility: support CREATE OR REPLACE VIEW syntax.

@roadmap_1387_h2
Not Planned

@roadmap_1388_li
HSQLDB (did) support this: select id i from test where i&lt;0 (other databases don't). Supporting it may break compatibility.

@roadmap_1389_li
String.intern (so that Strings can be compared with ==) will not be used because some VMs have problems when used extensively.

@search_1000_b
Search:

@search_1001_td
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@tutorial_1000_h1
Tutorial

@tutorial_1001_a
Starting and Using the H2 Console

@tutorial_1002_a
Settings of the H2 Console

@tutorial_1003_a
Connecting to a Database using JDBC

@tutorial_1004_a
Creating New Databases

@tutorial_1005_a
Using the Server

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Using Hibernate

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Using TopLink and Glassfish

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Using Databases in Web Applications

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CSV (Comma Separated Values) Support

@tutorial_1010_a
Upgrade, Backup, and Restore

@tutorial_1011_a
Command Line Tools

@tutorial_1012_a
Using OpenOffice Base

@tutorial_1013_a
Java Web Start / JNLP

@tutorial_1014_a
Using a Connection Pool

@tutorial_1015_a
Fulltext Search

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User-Defined Variables

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Date and Time

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Using Spring

@tutorial_1019_h2
Starting and Using the H2 Console

@tutorial_1020_p
The H2 Console application lets you access a SQL database using a browser interface. This can be a H2 database, or another database that supports the JDBC API.

@tutorial_1021_p
This is a client / server application, so both a server and a client (a browser) are required to run it.

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Depending on your platform and environment, there are multiple ways to start the application:

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OS

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Start

@tutorial_1025_td
Windows

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Click [Start], [All Programs], [H2], and [H2 Console (Command Line)]

@tutorial_1027_td
When using the Sun JDK 1.4 or 1.5, a window with the title 'H2 Console ' should appear.  When using the Sun JDK 1.6, an icon will be added to the system tray:

@tutorial_1028_td
If you don't get the window and the system tray icon,  then maybe Java is not installed correctly (in this case, try another way to start the application).  A browser window should open and point to the Login page at http://localhost:8082 .

@tutorial_1029_td
Windows

@tutorial_1030_td
Open a file browser, navigate to h2/bin, and double click on h2.bat.

@tutorial_1031_td
A console window appears. If there is a problem, you will see an error message  in this window. A browser window will open and point to the Login page  (URL: http://localhost:8082).

@tutorial_1032_td
Any

@tutorial_1033_td
Double click on the h2*.jar file.  This only works if the .jar suffix is associated with java.

@tutorial_1034_td
Any

@tutorial_1035_td
Open a console window, navigate to the directory 'h2/bin' and type:

@tutorial_1036_h3
Firewall

@tutorial_1037_p
If you start the server, you may get a security warning from the firewall (if you have installed one). If you don't want other computers in the network to access the application on your machine, you can let the firewall block those connections. The connection from the local machine will still work. Only if you want other computers to access the database on this computer, you need allow remote connections in the firewall.

@tutorial_1038_p
It has been reported that when using Kaspersky 7.0 with firewall, the H2 Console is very slow when connecting over the IP address. A workaround is to connect using localhost, however this only works on the local machine.

@tutorial_1039_p
A small firewall is already built into the server: other computers may not connect to the server by default. To change this, go to 'Preferences' and select 'Allow connections from other computers'.

@tutorial_1040_h3
Testing Java

@tutorial_1041_p
To find out which version of Java is installed, open a command prompt and type:

@tutorial_1042_p
If you get an error message, you may need to add the Java binary directory to the path environment variable.

@tutorial_1043_h3
Error Message 'Port may be in use'

@tutorial_1044_p
You can only start one instance of the H2 Console, otherwise you will get the following error message: <code>The Web server could not be started. Possible cause: another server is already running...</code> . It is possible to start multiple console applications on the same computer (using different ports), but this is usually not required as the console supports multiple concurrent connections.

@tutorial_1045_h3
Using another Port

@tutorial_1046_p
If the port is in use by another application, you may want to start the H2 Console on a different port. This can be done by changing the port in the file .h2.server.properties. This file is stored in the user directory (for Windows, this is usually in "Documents and Settings/&lt;username&gt;"). The relevant entry is webPort.

@tutorial_1047_h3
Connecting to the Server using a Browser

@tutorial_1048_p
If the server started successfully, you can connect to it using a web browser. JavaScript needs to be enabled. If you started the server on the same computer as the browser, open the URL http://localhost:8082 . If you want to connect to the application from another computer, you need to provide the IP address of the server, for example: http://192.168.0.2:8082 . If you enabled SSL on the server side, the URL needs to start with https:// .

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Multiple Concurrent Sessions

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Multiple concurrent browser sessions are supported. As that the database objects reside on the server, the amount of concurrent work is limited by the memory available to the server application.

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Login

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At the login page, you need to provide connection information to connect to a database. Set the JDBC driver class of your database, the JDBC URL, user name and password. If you are done, click [Connect].

@tutorial_1053_p
You can save and reuse previously saved settings. The settings are stored in a properties file (see <a href="#console_settings">Settings of the H2 Console</a> ).

@tutorial_1054_h3
Error Messages

@tutorial_1055_p
Error messages in are shown in red. You can show/hide the stack trace of the exception by clicking on the message.

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Adding Database Drivers

@tutorial_1057_p
Additional database drivers can be registered by adding the Jar file location of the driver to the environment variables H2DRIVERS or CLASSPATH. Example (Windows): To add the database driver library C:\Programs\hsqldb\lib\hsqldb.jar, set the environment variable H2DRIVERS to C:\Programs\hsqldb\lib\hsqldb.jar.

@tutorial_1058_p
Multiple drivers can be set; each entry needs to be separated with a ';' (Windows) or ':' (other operating systems). Spaces in the path names are supported. The settings must not be quoted.

@tutorial_1059_h3
Using the H2 Console

@tutorial_1060_p
The H2 Console application has three main panels: the toolbar on top, the tree on the left, and the query / result panel on the right. The database objects (for example, tables) are listed on the left panel. Type in a SQL command on the query panel and click 'Run'. The result of the command appears just below the command.

@tutorial_1061_h3
Inserting Table Names or Column Names

@tutorial_1062_p
The table name and column names can be inserted in the script by clicking them in the tree. If you click on a table while the query is empty, a 'SELECT * FROM ...' is added as well. While typing a query, the table that was used is automatically expanded in the tree. For, example if you type 'SELECT * FROM TEST T WHERE T.' then the table TEST is automatically expanded in the tree.

@tutorial_1063_h3
Disconnecting and Stopping the Application

@tutorial_1064_p
To log out of the database, click 'Disconnect' in the toolbar panel. However, the server is still running and ready to accept new sessions.

@tutorial_1065_p
To stop the server, right click on the system tray icon and select [Exit]. If you don't have the system tray icon, navigate to [Preferences] and click [Shutdown], press [Ctrl]+[C] in the console where the server was started (Windows), or close the console window.

@tutorial_1066_h2
Settings of the H2 Console

@tutorial_1067_p
The settings of the H2 Console are stored in a configuration file called <code>.h2.server.properties</code> in you user home directory. For Windows installations, the user home directory is usually <code>C:\Documents and Settings\[username]</code> . The configuration file contains the settings of the application and is automatically created when the H2 Console is first started.

@tutorial_1068_h2
Connecting to a Database using JDBC

@tutorial_1069_p
To connect to a database, a Java application first needs to load the database driver, and then get a connection. A simple way to do that is using the following code:

@tutorial_1070_p
This code first loads the driver ( <code>Class.forName(...)</code> ) and then opens a connection (using <code>DriverManager.getConnection()</code> ). The driver name is <code>"org.h2.Driver"</code> . The database URL always needs to start with <code>jdbc:h2:</code> to be recognized by this database. The second parameter in the <code>getConnection()</code> call is the user name ('sa' for System Administrator in this example). The third parameter is the password. In this database, user names are not case sensitive, but passwords are.

@tutorial_1071_h2
Creating New Databases

@tutorial_1072_p
By default, if the database specified in the URL does not yet exist, a new (empty) database is created automatically. The user that created the database automatically becomes the administrator of this database.

@tutorial_1073_h2
Using the Server

@tutorial_1074_p
H2 currently supports three server: a web server (for the H2 Console), a TCP server (for client/server connections) and an PG server (for PostgreSQL clients). The servers can be started in different ways, one is using the server tool.

@tutorial_1075_h3
Starting the Server Tool from Command Line

@tutorial_1076_p
To start the server tool from the command line with the default settings, run:

@tutorial_1077_p
This will start the server tool with the default options. To get the list of options and default values, run:

@tutorial_1078_p
There are options available to use other ports, and start or not start parts. For details, see the API documentation of the server tool.

@tutorial_1079_h3
Connecting to the TCP Server

@tutorial_1080_p
To remotely connect to a database using the TCP server, use the following driver and database URL:

@tutorial_1081_li
JDBC driver class: org.h2.Driver

@tutorial_1082_li
Database URL: jdbc:h2:tcp://localhost/~/test

@tutorial_1083_p
For details about the database URL, see also in Features.

@tutorial_1084_h3
Starting the TCP Server within an Application

@tutorial_1085_p
Servers can also be started and stopped from within an application. Sample code:

@tutorial_1086_h3
Stopping a TCP Server from Another Process

@tutorial_1087_p
The TCP server can be stopped from another process. To stop the server from the command line, run:

@tutorial_1088_p
To stop the server from a user application, use the following code:

@tutorial_1089_p
This function will only stop the TCP server. If other server were started in the same process, they will continue to run. To avoid recovery when the databases are opened the next time, all connections to the databases should be closed before calling this method. To stop a remote server, remote connections must be enabled on the server. Shutting down a TCP server can be protected using the option -tcpPassword (the same password must be used to start and stop the TCP server).

@tutorial_1090_h2
Using Hibernate

@tutorial_1091_p
This database supports Hibernate version 3.1 and newer. You can use the HSQLDB Dialect, or the native H2 Dialect. Unfortunately the H2 Dialect included in Hibernate is buggy. A <a href="http://opensource.atlassian.com/projects/hibernate/browse/HHH-3401">patch for Hibernate</a> has been submitted. The dialect for the newest version of Hibernate is also available at src/tools/org/hibernate/dialect/H2Dialect.java.txt. You can rename it to H2Dialect.java and include this as a patch in your application.

@tutorial_1092_h2
Using TopLink and Glassfish

@tutorial_1093_p
To use H2 with Glassfish (or Sun AS), set the Datasource Classname to <code>org.h2.jdbcx.JdbcDataSource</code> . You can set this in the GUI at Application Server - Resources - JDBC - Connection Pools, or by editing the file <code>sun-resources.xml</code> : at element <code>jdbc-connection-pool</code> , set the attribute <code>datasource-classname</code> to <code>org.h2.jdbcx.JdbcDataSource</code> .

@tutorial_1094_p
The H2 database is compatible with HSQLDB and PostgreSQL. To take advantage of H2 specific features, use the <code>H2Platform</code> . The source code of this platform is included in H2 at <code>src/tools/oracle/toplink/essentials/platform/database/DatabasePlatform.java.txt</code> . You will need to copy this file to your application, and rename it to .java. To enable it, change the following setting in persistence.xml:

@tutorial_1095_p
In old versions of Glassfish, the property name is <code>toplink.platform.class.name</code> .

@tutorial_1096_h2
Using Databases in Web Applications

@tutorial_1097_p
There are multiple ways to access a database from within web applications. Here are some examples if you use Tomcat or JBoss.

@tutorial_1098_h3
Embedded Mode

@tutorial_1099_p
The (currently) simplest solution is to use the database in the embedded mode, that means open a connection in your application when it starts (a good solution is using a Servlet Listener, see below), or when a session starts. A database can be accessed from multiple sessions and applications at the same time, as long as they run in the same process. Most Servlet Containers (for example Tomcat) are just using one process, so this is not a problem (unless you run Tomcat in clustered mode). Tomcat uses multiple threads and multiple classloaders. If multiple applications access the same database at the same time, you need to put the database jar in the shared/lib or server/lib directory. It is a good idea to open the database when the web application starts, and close it when the web application stops. If using multiple applications, only one (any) of them needs to do that. In the application, an idea is to use one connection per Session, or even one connection per request (action). Those connections should be closed after use if possible (but it's not that bad if they don't get closed).

@tutorial_1100_h3
Server Mode

@tutorial_1101_p
The server mode is similar, but it allows you to run the server in another process.

@tutorial_1102_h3
Using a Servlet Listener to Start and Stop a Database

@tutorial_1103_p
Add the h2*.jar file to your web application, and add the following snippet to your web.xml file (between the 'context-param' and the 'filter' section):

@tutorial_1104_p
For details on how to access the database, see the file DbStarter.java. By default the DbStarter listener opens an embedded connection using the database URL 'jdbc:h2:~/test', user name 'sa', and password 'sa'. If you want to use this connection within your servlet, you can access as follows:

@tutorial_1105_p
The DbStarter can also start the TCP server, however this is disabled by default. To enable it, use the parameter db.tcpServer in the file web.xml. Here is the complete list of options. These options need to be placed between the 'description' tag and the 'listener' / 'filter' tags:

@tutorial_1106_p
When the web application is stopped, the database connection will be closed automatically. If the TCP server is started within the DbStarter, it will also be stopped automatically.

@tutorial_1107_h3
Using the H2 Console Servlet

@tutorial_1108_p
The H2 Console is a standalone application and includes its own web server, but it can be used as a servlet as well. To do that, include the the h2 jar file in your application, and add the following configuration to your web.xml:

@tutorial_1109_p
For details, see also <code>src/tools/WEB-INF/web.xml</code> .

@tutorial_1110_p
To create a web application with just the H2 Console, run the following command:

@tutorial_1111_h2
CSV (Comma Separated Values) Support

@tutorial_1112_p
The CSV file support can be used inside the database using the functions CSVREAD and CSVWRITE, or it can be used outside the database as a standalone tool.

@tutorial_1113_h3
Writing a CSV File from Within a Database

@tutorial_1114_p
The built-in function CSVWRITE can be used to create a CSV file from a query. Example:

@tutorial_1115_h3
Reading a CSV File from Within a Database

@tutorial_1116_p
A CSV file can be read using the function CSVREAD. Example:

@tutorial_1117_h3
Writing a CSV File from a Java Application

@tutorial_1118_p
The CSV tool can be used in a Java application even when not using a database at all. Example:

@tutorial_1119_h3
Reading a CSV File from a Java Application

@tutorial_1120_p
It is possible to read a CSV file without opening a database. Example:

@tutorial_1121_h2
Upgrade, Backup, and Restore

@tutorial_1122_h3
Database Upgrade

@tutorial_1123_p
The recommended way to upgrade from one version of the database engine to the next version is to create a backup of the database (in the form of a SQL script) using the old engine, and then execute the SQL script using the new engine.

@tutorial_1124_h3
Backup using the Script Tool

@tutorial_1125_p
There are different ways to backup a database. For example, it is possible to copy the database files. However, this is not recommended while the database is in use. Also, the database files are not human readable and quite large. The recommended way to backup a database is to create a compressed SQL script file. This can be done using the Script tool:

@tutorial_1126_p
It is also possible to use the SQL command SCRIPT to create the backup of the database. For more information about the options, see the SQL command SCRIPT. The backup can be done remotely, however the file will be created on the server side. The built in FTP server could be used to retrieve the file from the server.

@tutorial_1127_h3
Restore from a Script

@tutorial_1128_p
To restore a database from a SQL script file, you can use the RunScript tool:

@tutorial_1129_p
For more information about the options, see the SQL command RUNSCRIPT. The restore can be done remotely, however the file needs to be on the server side. The built in FTP server could be used to copy the file to the server. It is also possible to use the SQL command RUNSCRIPT to execute a SQL script. SQL script files may contain references to other script files, in the form of RUNSCRIPT commands. However, when using the server mode, the references script files need to be available on the server side.

@tutorial_1130_h3
Online Backup

@tutorial_1131_p
The BACKUP SQL statement and the Backup tool both create a zip file with all database files. However, the contents of this file are not human readable. Other than the SCRIPT statement, the BACKUP statement does not lock the database objects, and therefore does not block other users. The resulting backup is transactionally consistent:

@tutorial_1132_p
The Backup tool (org.h2.tools.Backup) can not be used to create a online backup; the database must not be in use while running this program.

@tutorial_1133_h2
Command Line Tools

@tutorial_1134_p
This database comes with a number of command line tools. To get more information about a tool, start it with the parameter '-?', for example:

@tutorial_1135_p
The command line tools are:

@tutorial_1136_b
Backup

@tutorial_1137_li
creates a backup of a database.

@tutorial_1138_b
ChangeFileEncryption

@tutorial_1139_li
allows changing the file encryption password or algorithm of a database.

@tutorial_1140_b
Console

@tutorial_1141_li
starts the browser based H2 Console.

@tutorial_1142_b
ConvertTraceFile

@tutorial_1143_li
converts a .trace.db file to a Java application and SQL script.

@tutorial_1144_b
CreateCluster

@tutorial_1145_li
creates a cluster from a standalone database.

@tutorial_1146_b
DeleteDbFiles

@tutorial_1147_li
deletes all files belonging to a database.

@tutorial_1148_b
Recover

@tutorial_1149_li
helps recovering a corrupted database.

@tutorial_1150_b
Restore

@tutorial_1151_li
restores a backup of a database.

@tutorial_1152_b
RunScript

@tutorial_1153_li
runs a SQL script against a database.

@tutorial_1154_b
Script

@tutorial_1155_li
allows converting a database to a SQL script for backup or migration.

@tutorial_1156_b
Server

@tutorial_1157_li
is used in the server mode to start a H2 server.

@tutorial_1158_b
Shell

@tutorial_1159_li
is a command line database tool.

@tutorial_1160_p
The tools can also be called from an application by calling the main or another public method. For details, see the Javadoc documentation.

@tutorial_1161_h2
Using OpenOffice Base

@tutorial_1162_p
OpenOffice.org Base supports database access over the JDBC API. To connect to a H2 database using OpenOffice Base, you first need to add the JDBC driver to OpenOffice. The steps to connect to a H2 database are:

@tutorial_1163_li
Start OpenOffice Writer, go to [Tools], [Options]

@tutorial_1164_li
Make sure you have selected a Java runtime environment in OpenOffice.org / Java

@tutorial_1165_li
Click [Class Path...], [Add Archive...]

@tutorial_1166_li
Select your h2 jar file (location is up to you, could be wherever you choose)

@tutorial_1167_li
Click [OK] (as much as needed), stop OpenOffice (including the Quickstarter)

@tutorial_1168_li
Start OpenOffice Base

@tutorial_1169_li
Connect to an existing database; select [JDBC]; [Next]

@tutorial_1170_li
Example datasource URL: jdbc:h2:~/test

@tutorial_1171_li
JDBC driver class: org.h2.Driver

@tutorial_1172_p
Now you can access the database stored in the current users home directory.

@tutorial_1173_p
To use H2 in NeoOffice (OpenOffice without X11):

@tutorial_1174_li
In NeoOffice, go to [NeoOffice], [Preferences]

@tutorial_1175_li
Look for the page under [NeoOffice], [Java]

@tutorial_1176_li
Click [Class Path], [Add Archive...]

@tutorial_1177_li
Select your h2 jar file (location is up to you, could be wherever you choose)

@tutorial_1178_li
Click [OK] (as much as needed), restart NeoOffice.

@tutorial_1179_p
Now, when creating a new database using the "Database Wizard" :

@tutorial_1180_li
Click [File], [New], [Database].

@tutorial_1181_li
Select [Connect to existing database] and the select [JDBC]. Click next.

@tutorial_1182_li
Example datasource URL: jdbc:h2:~/test

@tutorial_1183_li
JDBC driver class: org.h2.Driver

@tutorial_1184_p
Another solution to use H2 in NeoOffice is:

@tutorial_1185_li
Package the h2 jar within an extension package

@tutorial_1186_li
Install it as a Java extension in NeoOffice

@tutorial_1187_p
This can be done by create it using the NetBeans OpenOffice plugin. See also <a href="http://wiki.services.openoffice.org/wiki/Extensions_development_java">Extensions Development</a> .

@tutorial_1188_h2
Java Web Start / JNLP

@tutorial_1189_p
When using Java Web Start / JNLP (Java Network Launch Protocol), permissions tags must be set in the .jnlp file, and the application .jar file must be signed. Otherwise, when trying to write to the file system, the following exception will occur: java.security.AccessControlException: access denied (java.io.FilePermission ... read). Example permission tags:

@tutorial_1190_h2
Using a Connection Pool

@tutorial_1191_p
For H2, opening a connection is fast if the database is already open. Still, using a connection pool improves performance if you open and close connections a lot. A simple connection pool is included in H2. It is based on the <a href="http://www.source-code.biz/snippets/java/8.htm">Mini Connection Pool Manager</a> from Christian d'Heureuse. There are other, more complex, open source connection pools available, for example the <a href="http://jakarta.apache.org/commons/dbcp/">Apache Commons DBCP</a> . For H2, it is about twice as faster to get a connection from the built-in connection pool than to get one using DriverManager.getConnection(). The build-in connection pool is used as follows:

@tutorial_1192_h2
Fulltext Search

@tutorial_1193_p
H2 includes two fulltext search implementations. One is using Apache Lucene, and the other (the native implementation) stores the index data in special tables in the database.

@tutorial_1194_h3
Using the Native Fulltext Search

@tutorial_1195_p
To initialize, call:

@tutorial_1196_p
You need to initialize it in each database where you want to use it. Afterwards, you can create a fulltext index for a table using:

@tutorial_1197_p
PUBLIC is the schema, TEST is the table name. The list of column names (column separated) is optional, in this case all columns are indexed. The index is updated in realtime. To search the index, use the following query:

@tutorial_1198_p
This will produce a result set that contains the query needed to retrieve the data:

@tutorial_1199_p
QUERY: "PUBLIC"."TEST" WHERE "ID"=1

@tutorial_1200_p
To get the raw data, use <code>FT_SEARCH_DATA('Hello', 0, 0);</code> . The result contains the columns SCHEMA (the schema name), TABLE (the table name), COLUMNS (an array of column names), and KEYS (an array of objects). To join a table, use a join as in: <code>SELECT T.* FROM FT_SEARCH_DATA('Hello', 0, 0) FT, TEST T WHERE FT.TABLE='TEST' AND T.ID= FT.KEYS[0];</code>

@tutorial_1201_p
You can also call the index from within a Java application:

@tutorial_1202_h3
Using the Lucene Fulltext Search

@tutorial_1203_p
To use the Lucene full text search, you need the Lucene library in the classpath. How to do that depends on the application; if you use the H2 Console, you can add the Lucene jar file to the environment variables H2DRIVERS or CLASSPATH. To initialize the Lucene fulltext search in a database, call:

@tutorial_1204_p
You need to initialize it in each database where you want to use it. Afterwards, you can create a full text index for a table using:

@tutorial_1205_p
PUBLIC is the schema, TEST is the table name. The list of column names (column separated) is optional, in this case all columns are indexed. The index is updated in realtime. To search the index, use the following query:

@tutorial_1206_p
This will produce a result set that contains the query needed to retrieve the data:

@tutorial_1207_p
QUERY: "PUBLIC"."TEST" WHERE "ID"=1

@tutorial_1208_p
To get the raw data, use <code>FTL_SEARCH_DATA('Hello', 0, 0);</code> . The result contains the columns SCHEMA (the schema name), TABLE (the table name), COLUMNS (an array of column names), and KEYS (an array of objects). To join a table, use a join as in: <code>SELECT T.* FROM FTL_SEARCH_DATA('Hello', 0, 0) FT, TEST T WHERE FT.TABLE='TEST' AND T.ID= FT.KEYS[0];</code>

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You can also call the index from within a Java application:

@tutorial_1210_h2
User-Defined Variables

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This database supports user-defined variables. Variables start with @ and can be used wherever expressions or parameters are allowed. Variables are not persisted and session scoped, that means only visible from within the session in which they are defined. A value is usually assigned using the SET command:

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The value can also be changed using the SET() method. This is useful in queries:

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Variables that are not set evaluate to NULL. The data type of a user-defined variable is the data type of the value assigned to it, that means it is not necessary (or possible) to declare variable names before using them. There are no restrictions on the assigned values; large objects (LOBs) are supported as well.

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Date and Time

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Date, time and timestamp values support ISO 8601 formatting, including time zone:

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If the time zone is not set, the value is parsed using the current time zone setting of the system. Date and time information is stored in H2 database files in GMT (Greenwich Mean Time). If the database is opened using another system time zone, the date and time will change accordingly. If you want to move a database from one time zone to the other and don't want this to happen, you need to create a SQL script file using the SCRIPT command or Script tool, and then load the database using the RUNSCRIPT command or the RunScript tool in the new time zone.

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Using Spring

@tutorial_1218_p
Use the following configuration to start and stop the H2 TCP server using the Spring Framework:

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The "destroy-method" will help prevent exceptions on hot-redeployment or when restarting the server.