--no commit message

--no commit message

h2/src/docsrc/html/advanced.html

@@ -20,6 +20,8 @@ Advanced Topics
     Linked Tables</a><br />
 <a href="#transaction_isolation">
     Transaction Isolation</a><br />
+<a href="#mvcc">
+    Multi-Version Concurrency Control (MVCC)</a><br />
 <a href="#clustering">
     Clustering / High Availability</a><br />
 <a href="#two_phase_commit">
@@ -176,6 +178,26 @@ connection will get a lock timeout exception. The lock timeout can be set indivi
 for each connection.
 </p>
 
+<br /><a name="mvcc"></a>
+<h2>Multi-Version Concurrency Control (MVCC)</h2>
+<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. Table are still locked exclusively 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. 
+</p>
+<p>
+To use the MVCC feature, append MVCC=TRUE to the database URL:
+<pre>
+jdbc:h2:~/test;MVCC=TRUE
+</pre>
+</p>
+
 <br /><a name="clustering"></a>
 <h2>Clustering / High Availability</h2>
 <p>

h2/src/main/org/h2/table/TableData.java

@@ -311,20 +311,20 @@ public class TableData extends Table implements RecordReader {
             return;
         }
         long max = System.currentTimeMillis() + session.getLockTimeout();
-        synchronized (database) {
-            while (true) {
-                if (lockExclusive == session) {
-                    return;
-                }
         if (!force && database.isMultiVersion()) {
             // MVCC: update, delete, and insert use a shared lock
-                    // but select doesn't lock
+            // select doesn't lock
             if (exclusive) {
                 exclusive = false;
             } else {
                 return;
             }
         }
+        synchronized (database) {
+            while (true) {
+                if (lockExclusive == session) {
+                    return;
+                }
                 if (exclusive) {
                     if (lockExclusive == null) {
                         if (lockShared.isEmpty()) {

h2/src/test/org/h2/test/TestAll.java

@@ -142,15 +142,6 @@ java org.h2.test.TestAll timer
 
 /*
 
-
-TODO history:
-Math operations using unknown data types (for example -? and ?+?) are now interpreted as decimal.
-INSTR, LOCATE: backward searching is not supported by using a negative start position
-
-TODO doc:
-MVCC still locks the table exclusively when adding or removing columns and when dropping the table.
-Also, a shared lock is still added when inserting or removing rows.
-
 replicating file system
 background thread writing file system (all writes)
 

h2/src/test/org/h2/test/mvcc/TestMVCC.java

@@ -40,13 +40,14 @@ public class TestMVCC extends TestBase {
 
         DeleteDbFiles.execute(null, "test", true);
         Class.forName("org.h2.Driver");
-        c1 = DriverManager.getConnection("jdbc:h2:test;MVCC=TRUE", "sa", "sa");
+        c1 = DriverManager.getConnection("jdbc:h2:test;MVCC=TRUE;LOCK_TIMEOUT=10", "sa", "sa");
         s1 = c1.createStatement();
-        c2 = DriverManager.getConnection("jdbc:h2:test;MVCC=TRUE", "sa", "sa");
+        c2 = DriverManager.getConnection("jdbc:h2:test;MVCC=TRUE;LOCK_TIMEOUT=10", "sa", "sa");
         s2 = c2.createStatement();
         c1.setAutoCommit(false);
         c2.setAutoCommit(false);
         
+        // it should not be possible to drop a table when an uncommitted transaction changed something
         s1.execute("create table test(id int primary key)");
         s1.execute("insert into test values(1)");
         try {
@@ -60,6 +61,23 @@ public class TestMVCC extends TestBase {
         s2.execute("drop table test");
         c2.rollback();
         
+        // select for update should do an exclusive lock, even with mvcc
+        s1.execute("create table test(id int primary key, name varchar(255))");
+        s1.execute("insert into test values(1, 'y')");
+        c1.commit();
+        s2.execute("select * from test for update");
+        try {
+            s1.execute("insert into test values(2, 'x')");
+            error("Unexpected success");
+        } catch (SQLException e) {
+            // lock timeout expected
+            checkNotGeneralException(e);
+        }
+        c2.rollback();
+        s1.execute("drop table test");
+        c1.commit();
+        c2.commit();
+        
         s1.execute("create table test(id int primary key, name varchar(255))");
         s2.execute("insert into test values(4, 'Hello')");
         c2.rollback();

h2/src/test/org/h2/test/testSimple.in.txt

-select instr('asgisj','s', -1) from dual;
+select instr('abcisj','s', -1) from dual;
 > 5;
 CREATE TABLE TEST(ID INT);
 INSERT INTO TEST VALUES(1), (2), (3);