Skip to content

H
h2database
切换分支/标签
查找文件
Normal viewHistoryPermalink
performance.html 26.3 KB
Newer Older
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
1 2 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<!--
Thomas Mueller's avatar
update copyright
84595889
 
Thomas Mueller committed
3 
Copyright 2004-2009 H2 Group. Multiple-Licensed under the H2 License, Version 1.0,
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 
and under the Eclipse Public License, Version 1.0
(http://h2database.com/html/license.html).
Initial Developer: H2 Group
-->
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head><meta http-equiv="Content-Type" content="text/html;charset=utf-8" /><title>
Performance
</title><link rel="stylesheet" type="text/css" href="stylesheet.css" />
<!-- [search] { -->
<script type="text/javascript" src="navigation.js"></script>
</head><body onload="frameMe();">
<table class="content"><tr class="content"><td class="content"><div class="contentDiv">
<!-- } -->

<h1>Performance</h1>
<a href="#performance_comparison">
    Performance Comparison</a><br />
<a href="#poleposition_benchmark">
    PolePosition Benchmark</a><br />
<a href="#application_profiling">
    Application Profiling</a><br />
<a href="#database_profiling">
    Database Profiling</a><br />
<a href="#database_performance_tuning">
Thomas Mueller's avatar
--no commit message
a5505f83
 
Thomas Mueller committed
28 
    Database Performance Tuning</a><br />
Thomas Mueller's avatar
Improved docs.
27d7b7d3
 
Thomas Mueller committed
29 30 
<a href="#fast_import">
    Fast Database Import</a><br />
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
31
Thomas Mueller's avatar
docs
da30c87b
 
Thomas Mueller committed
32 
<h2 id="performance_comparison">Performance Comparison</h2>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
33 
<p>
Thomas Mueller's avatar
--no commit message
b5045419
 
Thomas Mueller committed
34 
In many cases H2 is faster than other
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
35 36 37 38 39 40 41 
(open source and not open source) database engines.
Please note this is mostly a single connection benchmark run on one computer.
</p>

<h3>Embedded</h3>
<table border="1" class="bar">
<tr><th>Test Case</th><th>Unit</th><th>H2</th><th>HSQLDB</th><th>Derby</th></tr>
Thomas Mueller's avatar
prepare release
b34ed604
 
Thomas Mueller committed
42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 
<tr><td>Simple: Init</td><td>ms</td><td>547</td><td>532</td><td>2594</td></tr>
<tr><td>Simple: Query (random)</td><td>ms</td><td>250</td><td>391</td><td>1515</td></tr>
<tr><td>Simple: Query (sequential)</td><td>ms</td><td>188</td><td>313</td><td>1406</td></tr>
<tr><td>Simple: Update (random)</td><td>ms</td><td>812</td><td>1750</td><td>17704</td></tr>
<tr><td>Simple: Delete (sequential)</td><td>ms</td><td>203</td><td>250</td><td>8843</td></tr>
<tr><td>Simple: Memory Usage</td><td>MB</td><td>7</td><td>11</td><td>11</td></tr>
<tr><td>BenchA: Init</td><td>ms</td><td>578</td><td>719</td><td>3328</td></tr>
<tr><td>BenchA: Transactions</td><td>ms</td><td>3047</td><td>2406</td><td>12907</td></tr>
<tr><td>BenchA: Memory Usage</td><td>MB</td><td>10</td><td>15</td><td>10</td></tr>
<tr><td>BenchB: Init</td><td>ms</td><td>2141</td><td>2406</td><td>11562</td></tr>
<tr><td>BenchB: Transactions</td><td>ms</td><td>1125</td><td>1375</td><td>3625</td></tr>
<tr><td>BenchB: Memory Usage</td><td>MB</td><td>9</td><td>11</td><td>8</td></tr>
<tr><td>BenchC: Init</td><td>ms</td><td>688</td><td>594</td><td>4500</td></tr>
<tr><td>BenchC: Transactions</td><td>ms</td><td>1906</td><td>64062</td><td>6047</td></tr>
<tr><td>BenchC: Memory Usage</td><td>MB</td><td>11</td><td>17</td><td>11</td></tr>
<tr><td>Executed statements</td><td>#</td><td>322929</td><td>322929</td><td>322929</td></tr>
<tr><td>Total time</td><td>ms</td><td>11485</td><td>74798</td><td>74031</td></tr>
<tr><td>Statements per second</td><td>#</td><td>28117</td><td>4317</td><td>4362</td></tr>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
60 61 62 63 64 
</table>

<h3>Client-Server</h3>
<table border="1" class="bar">
<tr><th>Test Case</th><th>Unit</th><th>H2</th><th>HSQLDB</th><th>Derby</th><th>PostgreSQL</th><th>MySQL</th></tr>
Thomas Mueller's avatar
prepare release
b34ed604
 
Thomas Mueller committed
65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 
<tr><td>Simple: Init</td><td>ms</td><td>2782</td><td>2656</td><td>5625</td><td>4563</td><td>3484</td></tr>
<tr><td>Simple: Query (random)</td><td>ms</td><td>3093</td><td>2703</td><td>6688</td><td>4812</td><td>3860</td></tr>
<tr><td>Simple: Query (sequential)</td><td>ms</td><td>2969</td><td>2594</td><td>6437</td><td>4719</td><td>3625</td></tr>
<tr><td>Simple: Update (random)</td><td>ms</td><td>2969</td><td>3531</td><td>18250</td><td>5953</td><td>5125</td></tr>
<tr><td>Simple: Delete (sequential)</td><td>ms</td><td>1047</td><td>1250</td><td>6875</td><td>2485</td><td>2390</td></tr>
<tr><td>Simple: Memory Usage</td><td>MB</td><td>7</td><td>11</td><td>14</td><td>0</td><td>0</td></tr>
<tr><td>BenchA: Init</td><td>ms</td><td>2250</td><td>2453</td><td>6031</td><td>4328</td><td>3625</td></tr>
<tr><td>BenchA: Transactions</td><td>ms</td><td>10250</td><td>9016</td><td>21484</td><td>15609</td><td>11172</td></tr>
<tr><td>BenchA: Memory Usage</td><td>MB</td><td>10</td><td>15</td><td>10</td><td>0</td><td>1</td></tr>
<tr><td>BenchB: Init</td><td>ms</td><td>9500</td><td>10672</td><td>22609</td><td>19609</td><td>13406</td></tr>
<tr><td>BenchB: Transactions</td><td>ms</td><td>2734</td><td>2656</td><td>3875</td><td>4688</td><td>2531</td></tr>
<tr><td>BenchB: Memory Usage</td><td>MB</td><td>10</td><td>11</td><td>11</td><td>1</td><td>1</td></tr>
<tr><td>BenchC: Init</td><td>ms</td><td>1860</td><td>1484</td><td>6890</td><td>2219</td><td>3438</td></tr>
<tr><td>BenchC: Transactions</td><td>ms</td><td>9046</td><td>63266</td><td>18641</td><td>11703</td><td>7421</td></tr>
<tr><td>BenchC: Memory Usage</td><td>MB</td><td>12</td><td>17</td><td>13</td><td>0</td><td>1</td></tr>
<tr><td>Executed statements</td><td>#</td><td>322929</td><td>322929</td><td>322929</td><td>322929</td><td>322929</td></tr>
<tr><td>Total time</td><td>ms</td><td>48500</td><td>102281</td><td>123405</td><td>80688</td><td>60077</td></tr>
<tr><td>Statements per second</td><td>#</td><td>6658</td><td>3157</td><td>2616</td><td>4002</td><td>5375</td></tr>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
83 84 85 86 87 88 
</table>

<h3>Benchmark Results and Comments</h3>

<h4>H2</h4>
<p>
Thomas Mueller's avatar
prepare release
b34ed604
 
Thomas Mueller committed
89 
Version 1.1.114 (2009-06-01) was used for the test.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
90 91 92 93 94 95 
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.
Thomas Mueller's avatar
Improved docs.
27d7b7d3
 
Thomas Mueller committed
96 
The open/close time is almost fixed, because of the file locking protocol: the engine waits
Thomas Mueller's avatar
Improve docs
d22a1a41
 
Thomas Mueller committed
97 
some time after opening a database to ensure the database files are not opened by another process.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
98 99 100 101 102 103 
</p>

<h4>HSQLDB</h4>
<p>
Version 1.8.0.10 was used for the test.
Cached tables are used in this test (hsqldb.default_table_type=cached),
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
104 
and the write delay is 1 second (<code>SET WRITE_DELAY 1</code>).
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
105 106 107 108 
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:
</p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
109 
<pre>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
110 
SELECT COUNT(DISTINCT S_I_ID) FROM ORDER_LINE, STOCK
Thomas Mueller's avatar
--no commit message
554a5c0f
 
Thomas Mueller committed
111 
WHERE OL_W_ID=? AND OL_D_ID=? AND OL_O_ID&lt;? AND OL_O_ID&gt;=?
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
112 113 114 115 
AND S_W_ID=? AND S_I_ID=OL_I_ID AND S_QUANTITY&lt;?
</pre>
<p>
The PolePosition benchmark also shows that the query optimizer does not do a very good job for some queries.
Thomas Mueller's avatar
Improve docs
d22a1a41
 
Thomas Mueller committed
116 117 
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.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
118 119 120 121 122 123 
</p>

<h4>Derby</h4>
<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.
Thomas Mueller's avatar
Improve docs
d22a1a41
 
Thomas Mueller committed
124 
It will be hard for the developers of Derby to improve the performance to a reasonable level.
Thomas Mueller's avatar
Improved docs.
27d7b7d3
 
Thomas Mueller committed
125 
A few problems have been identified: leaving autocommit on is a problem for Derby.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
126 
If it is switched off during the whole test, the results are about 20% better for Derby.
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
127 
Derby supports a testing mode (system property <code>derby.system.durability=test</code>) where durability is
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
128 129 130 131 132 133 134 135 
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.
</p>

<h4>PostgreSQL</h4>
<p>
Thomas Mueller's avatar
prepare release
b34ed604
 
Thomas Mueller committed
136 
Version 8.3.7 was used for the test.
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
137 
The following options where changed in <code>postgresql.conf:
Thomas Mueller's avatar
Documentation: added notranslate tags
a08877c0
 
Thomas Mueller committed
138 
fsync = off, commit_delay = 1000</code>.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
139 140 141 142 143 144 145 
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.
</p>

<h4>MySQL</h4>
<p>
Thomas Mueller's avatar
prepare release
b34ed604
 
Thomas Mueller committed
146 
Version 5.1.34-community was used for the test.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
147 
MySQL was run with the InnoDB backend.
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
148 149 
The setting <code>innodb_flush_log_at_trx_commit</code>
(found in the <code>my.ini</code> file) was set to 0. Otherwise (and by default), MySQL is really slow
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
150 151 152 153 154 
(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.
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
155 
You need to change this setting manually in the file <code>my.ini</code>, and then restart the service.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 
The memory usage number is incorrect, because only the memory usage of the JDBC driver is measured.
</p>

<h4>Firebird</h4>
<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.
</p>

<h4>Why Oracle / MS SQL Server / DB2 are Not Listed</h4>
<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.
</p>

<h3>About this Benchmark</h3>
Thomas Mueller's avatar
--no commit message
554a5c0f
 
Thomas Mueller committed
176 177 178 179 
<h4>How to Run</h4>
<p>
This test was executed as follows:
</p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
180 
<pre>
Thomas Mueller's avatar
--no commit message
554a5c0f
 
Thomas Mueller committed
181 182 183 184 185 186 187 188 189 
build benchmark
</pre>

<h4>Separate Process per Database</h4>
<p>
For each database, a new process is started, to ensure the previous test does not impact
the current test.
</p>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
190 191 192 193 194 195 196 197 
<h4>Number of Connections</h4>
<p>
This is mostly a single-connection benchmark.
BenchB uses multiple connections; the other tests use one connection.
</p>

<h4>Real-World Tests</h4>
<p>
Thomas Mueller's avatar
Improved docs.
27d7b7d3
 
Thomas Mueller committed
198 199 
Good benchmarks emulate real-world use cases. This benchmark includes 4 test cases:
BenchSimple uses one table and many small updates / deletes.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
200 201 202 203 204 205 206 207 
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.
</p>

<h4>Comparing Embedded with Server Databases</h4>
<p>
This is mainly a benchmark for embedded databases (where the application runs in the same
Thomas Mueller's avatar
Improve docs
d22a1a41
 
Thomas Mueller committed
208 
virtual machine as the database engine). However MySQL and PostgreSQL are not Java
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 
databases and cannot be embedded into a Java application.
For the Java databases, both embedded and server modes are tested.
</p>

<h4>Test Platform</h4>
<p>
This test is run on Windows XP with the virus scanner switched off.
The VM used is Sun JDK 1.5.
</p>

<h4>Multiple Runs</h4>
<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.
</p>

<h4>Memory Usage</h4>
<p>
It is not enough to measure the time taken, the memory usage is important as well.
Thomas Mueller's avatar
Improve docs
d22a1a41
 
Thomas Mueller committed
230 
Performance can be improved by using a bigger cache, but the amount of memory is limited.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 
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.
</p>

<h4>Delayed Operations</h4>
<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).
</p>

<h4>Transaction Commit / Durability</h4>
<p>
Durability means transaction committed to the database will not be lost.
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
248 249 
Some databases (for example MySQL) try to enforce this by default by
calling <code>fsync()</code> to flush the buffers, but
Thomas Mueller's avatar
Documentation: added notranslate tags
a08877c0
 
Thomas Mueller committed
250 
most hard drives don't actually flush all data. Calling the method slows down transaction commit a lot,
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 
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.
</p>

<h4>Using Prepared Statements</h4>
<p>
Wherever possible, the test cases use prepared statements.
</p>

<h4>Currently Not Tested: Startup Time</h4>
<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.
</p>
Thomas Mueller's avatar
docs
da30c87b
 
Thomas Mueller committed
274 
<h2 id="poleposition_benchmark">PolePosition Benchmark</h2>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 
<p>
The PolePosition is an open source benchmark. The algorithms are all quite simple.
It was developed / sponsored by db4o.
</p>
<table border="1" class="bar">
<tr><th>Test Case</th><th>Unit</th><th>H2</th><th>HSQLDB</th><th>MySQL</th></tr>
<tr><td>Melbourne write</td><td>ms</td><td>369</td><td>249</td><td>2022</td></tr>
<tr><td>Melbourne read</td><td>ms</td><td>47</td><td>49</td><td>93</td></tr>
<tr><td>Melbourne read_hot</td><td>ms</td><td>24</td><td>43</td><td>95</td></tr>
<tr><td>Melbourne delete</td><td>ms</td><td>147</td><td>133</td><td>176</td></tr>
<tr><td>Sepang write</td><td>ms</td><td>965</td><td>1201</td><td>3213</td></tr>
<tr><td>Sepang read</td><td>ms</td><td>765</td><td>948</td><td>3455</td></tr>
<tr><td>Sepang read_hot</td><td>ms</td><td>789</td><td>859</td><td>3563</td></tr>
<tr><td>Sepang delete</td><td>ms</td><td>1384</td><td>1596</td><td>6214</td></tr>
<tr><td>Bahrain write</td><td>ms</td><td>1186</td><td>1387</td><td>6904</td></tr>
<tr><td>Bahrain query_indexed_string</td><td>ms</td><td>336</td><td>170</td><td>693</td></tr>
<tr><td>Bahrain query_string</td><td>ms</td><td>18064</td><td>39703</td><td>41243</td></tr>
<tr><td>Bahrain query_indexed_int</td><td>ms</td><td>104</td><td>134</td><td>678</td></tr>
<tr><td>Bahrain update</td><td>ms</td><td>191</td><td>87</td><td>159</td></tr>
<tr><td>Bahrain delete</td><td>ms</td><td>1215</td><td>729</td><td>6812</td></tr>
<tr><td>Imola retrieve</td><td>ms</td><td>198</td><td>194</td><td>4036</td></tr>
<tr><td>Barcelona write</td><td>ms</td><td>413</td><td>832</td><td>3191</td></tr>
<tr><td>Barcelona read</td><td>ms</td><td>119</td><td>160</td><td>1177</td></tr>
<tr><td>Barcelona query</td><td>ms</td><td>20</td><td>5169</td><td>101</td></tr>
<tr><td>Barcelona delete</td><td>ms</td><td>388</td><td>319</td><td>3287</td></tr>
<tr><td>Total</td><td>ms</td><td>26724</td><td>53962</td><td>87112</td></tr>
</table>
Thomas Mueller's avatar
new experimental page store
390ecb87
 
Thomas Mueller committed
302 303 304 
<p>
There are a few problems with the PolePosition test:
</p>
Thomas Mueller's avatar
--no commit message
03d917b3
 
Thomas Mueller committed
305 306 307 
<ul><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
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
308 309 
<code>poleposition-0.20/lib/hsqldb.jar</code> with a newer version (for example
<code>hsqldb-1.8.0.7.jar</code>),
Thomas Mueller's avatar
--no commit message
03d917b3
 
Thomas Mueller committed
310 
and then use the setting
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
311 312 
<code>hsqldb.connecturl=jdbc:hsqldb:file:data/hsqldb/dbbench2;hsqldb.default_table_type=cached;sql.enforce_size=true</code>
in the file <code>Jdbc.properties</code>.
Thomas Mueller's avatar
--no commit message
03d917b3
 
Thomas Mueller committed
313 
</li><li>HSQLDB keeps the database open between tests, while H2 closes the database (losing all the cache).
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
314 
To change that, use the database URL <code>jdbc:h2:file:data/h2/dbbench;DB_CLOSE_DELAY=-1</code>
Thomas Mueller's avatar
--no commit message
03d917b3
 
Thomas Mueller committed
315 
</li><li>The amount of cache memory is quite important, specially for the PolePosition test.
Thomas Mueller's avatar
new experimental page store
390ecb87
 
Thomas Mueller committed
316 317 
Unfortunately, the PolePosition test does not take this into account.
</li></ul>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
318
Thomas Mueller's avatar
docs
da30c87b
 
Thomas Mueller committed
319 
<h2 id="application_profiling">Application Profiling</h2>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
320 321 322 

<h3>Analyze First</h3>
<p>
Thomas Mueller's avatar
improve documentation
613ec072
 
Thomas Mueller committed
323 324 325 
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
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
326 
<code>System.currentTimeMillis()</code>. But this does not work for complex applications with many modules, and for memory problems.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
327 328 
</p>
<p>
Thomas Mueller's avatar
improve documentation
613ec072
 
Thomas Mueller committed
329 330 
A good tool to measure both memory usage and performance is the
<a href="http://www.yourkit.com">YourKit Java Profiler</a>.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
331 332 333 334 
</p>
<p>
A simple way to profile an application is to use the built-in profiling tool of java. Example:
</p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
335 
<pre>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
336 337 338 
java -Xrunhprof:cpu=samples,depth=16 com.acme.Test
</pre>
<p>
Thomas Mueller's avatar
improve documentation
613ec072
 
Thomas Mueller committed
339 
Unfortunately, it is only possible to profile the application from start to end. Another solution is to create
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
340 341 
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
Thomas Mueller's avatar
improve documentation
613ec072
 
Thomas Mueller committed
342 
Ctrl+C (Windows).
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
343 344 
</p>
Thomas Mueller's avatar
docs
da30c87b
 
Thomas Mueller committed
345 
<h2 id="database_profiling">Database Profiling</h2>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
346 
<p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
347 348 
The <code>ConvertTraceFile</code> 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 <code>java -Xrunhprof</code>.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
349 350 
As an example, execute the the following script using the H2 Console:
</p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
351 
<pre>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
352 353 354 355 356 357 358 
SET TRACE_LEVEL_FILE 3;
DROP TABLE IF EXISTS TEST;
CREATE TABLE TEST(ID INT PRIMARY KEY, NAME VARCHAR(255));
@LOOP 1000 INSERT INTO TEST VALUES(?, ?);
SET TRACE_LEVEL_FILE 0;
</pre>
<p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
359 
Now convert the <code>.trace.db</code> file using the <code>ConvertTraceFile</code> tool:
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
360 
</p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
361 
<pre>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
362 
java -cp h2*.jar org.h2.tools.ConvertTraceFile
Thomas Mueller's avatar
indentation
d7b57e07
 
Thomas Mueller committed
363 
    -traceFile "~/test.trace.db" -script "~/test.sql"
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
364 365 
</pre>
<p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
366 
The generated file <code>test.sql</code> will contain the SQL statements as well as the
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
367 368 
following profiling data (results vary):
</p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
369 
<pre>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
370 371 372 373 374 375 376 377 378 379 380 381 382 
-----------------------------------------
-- SQL Statement Statistics
-- time: total time in milliseconds (accumulated)
-- count: how many times the statement ran
-- result: total update count or row count
-----------------------------------------
-- self accu    time   count  result sql
--  62%  62%     158    1000    1000 INSERT INTO TEST VALUES(?, ?);
--  37% 100%      93       1       0 CREATE TABLE TEST(ID INT PRIMARY KEY, NAME VARCHAR(255));
--   0% 100%       0       1       0 DROP TABLE IF EXISTS TEST;
--   0% 100%       0       1       0 SET TRACE_LEVEL_FILE 3;
</pre>
Thomas Mueller's avatar
docs
da30c87b
 
Thomas Mueller committed
383 
<h2 id="database_performance_tuning">Database Performance Tuning</h2>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
384
Thomas Mueller's avatar
Shortened the paragraph, removed unnecessary information.
6061376c
 
Thomas Mueller committed
385 386 
<h3>Use a Modern JVM</h3>
<p>
Thomas Mueller's avatar
Formatting fixes.
0f61802b
 
Thomas Mueller committed
387 
Newer JVMs are faster. Upgrading to the latest version of your JVM can provide a "free" boost to performance.
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
388 
Switching from the default Client JVM to the Server JVM using the <code>-server</code> command-line
Thomas Mueller's avatar
--no commit message
7f75c8c0
 
Thomas Mueller committed
389 
option improves performance at the cost of a slight increase in start-up time.
buckyballs's avatar
Docs-Performance: JVM choice & Data Types
4c33d834
 
buckyballs committed
390 391 
</p>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
392 393 394 395 
<h3>Virus Scanners</h3>
<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.
Thomas Mueller's avatar
--no commit message
7f75c8c0
 
Thomas Mueller committed
396 
The database engine never interprets the data stored in the files as programs,
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
397 398 
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).
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
399 
Some virus scanners allow to exclude files by suffix. Ensure files ending with <code>.db</code> are not scanned.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
400 401 402 403 
</p>

<h3>Using the Trace Options</h3>
<p>
Thomas Mueller's avatar
--no commit message
7f75c8c0
 
Thomas Mueller committed
404 
If the performance hot spots are in the database engine, in many cases the performance
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
405 406 407 408 409 410 411 412 
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>.
</p>

<h3>Index Usage</h3>
<p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
413 414 415 
This database uses indexes to improve the performance of
<code>SELECT, UPDATE, DELETE</code>.
If a column is used in the <code>WHERE</code> clause of a query, and if an index exists on this column,
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
416 417 
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.
Thomas Mueller's avatar
improve documentation
613ec072
 
Thomas Mueller committed
418 419 
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.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
420 421 
Indexes are created automatically for primary key and unique constraints.
Indexes are also created for foreign key constraints, if required.
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
422 
For other columns, indexes need to be created manually using the <code>CREATE INDEX</code> statement.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 
</p>

<h3>Optimizer</h3>
<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.
</p>

<h3>Expression Optimization</h3>
<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).
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
440 
If the <code>WHERE</code> clause is always false, then the table is not accessed at all.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
441 442 443 444 445 
</p>

<h3>COUNT(*) Optimization</h3>
<p>
If the query only counts all rows of a table, then the data is not accessed.
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
446 447 
However, this is only possible if no <code>WHERE</code> clause is used, that means it only works for
queries of the form <code>SELECT COUNT(*) FROM table</code>.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
448 449 450 451 452 453 
</p>

<h3>Updating Optimizer Statistics / Column Selectivity</h3>
<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.
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
454 455 
Example: for the query
<code>SELECT * FROM TEST T1, TEST T2 WHERE T1.NAME='A' AND T2.ID=T1.ID</code>,
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
456 457 458 
two index can be used, in this case the index on NAME for T1 and the index on ID for T2.
</p><p>
If a table has multiple indexes, sometimes more than one index could be used.
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
459 460 
Example: if there is a table <code>TEST(ID, NAME, FIRSTNAME)</code> and an index on each column,
then two indexes could be used for the query <code>SELECT * FROM TEST WHERE NAME='A' AND FIRSTNAME='B'</code>,
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
461 462 463 464 465 466 
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.
</p><p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
467 
The SQL statement <code>ANALYZE</code> can be used to automatically estimate the selectivity of the columns in the tables.
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
468 469 470 
This command should be run from time to time to improve the query plans generated by the optimizer.
</p>
Thomas Mueller's avatar
--no commit message
a5505f83
 
Thomas Mueller committed
471 472 473 474 475 476 477 
<h3>In-Memory (Hash) Indexes</h3>
<p>
Using in-memory indexes, specially in-memory hash indexes, can speed up
queries and data manipulation.
</p>
<p>In-memory indexes are automatically used
for in-memory databases, but can also be created for persistent databases
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
478 
using <code>CREATE MEMORY TABLE</code>. In many cases,
Thomas Mueller's avatar
--no commit message
a5505f83
 
Thomas Mueller committed
479 480 481 482 483 
the rows itself will also be kept in-memory. Please note this may cause memory
problems for large tables.
</p>
<p>
In-memory hash indexes are backed by a hash table and are usually faster than
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
484 485 486 487 
regular indexes. However, hash indexes only supports direct lookup (<code>WHERE ID = ?</code>)
but not range scan (<code>WHERE ID &lt; ?</code>). To use hash indexes, use HASH as in:
<code>CREATE UNIQUE HASH INDEX</code> and
<code>CREATE TABLE ...(ID INT PRIMARY KEY HASH,...)</code>.
Thomas Mueller's avatar
--no commit message
a5505f83
 
Thomas Mueller committed
488 489 
</p>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
490 491 
<h3>Optimization Examples</h3>
<p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
492 
See <code>src/test/org/h2/samples/optimizations.sql</code> for a few examples of queries
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
493 494 495 
that benefit from special optimizations built into the database.
</p>
Thomas Mueller's avatar
--no commit message
c7038f81
 
Thomas Mueller committed
496 497 498 499 500 501 
<h3>Cache Size and Type</h3>
<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>.
</p>
buckyballs's avatar
Docs-Performance: JVM choice & Data Types
4c33d834
 
buckyballs committed
502 503 504 
<h3>Data Types</h3>
<p>
Each data type has different storage and performance characteristics:
Thomas Mueller's avatar
Formatting fixes.
0f61802b
 
Thomas Mueller committed
505 
</p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
506 507 
<ul><li>The <code>DECIMAL/NUMERIC</code> type is slower
    and requires more storage than the <code>REAL</code> and <code>DOUBLE</code> types.
buckyballs's avatar
Docs-Performance: JVM choice & Data Types
4c33d834
 
buckyballs committed
508 
</li><li>Text types are slower to read, write, and compare than numeric types and generally require more storage.
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
509 510 511 512 513 514 515 516 
</li><li>See <a href="advanced.html#large_objects">Large Objects</a> for information on
    <code>BINARY</code> vs. <code>BLOB</code>
    and <code>VARCHAR</code> vs. <code>CLOB</code> performance.
</li><li>Parsing and formatting takes longer for the
    <code>TIME</code>, <code>DATE</code>, and
    <code>TIMESTAMP</code> types than the numeric types.
</li><li><code>SMALLINT/TINYINT/BOOLEAN</code> are not significantly smaller or faster
    to work with than <code>INTEGER</code> in most modes.
Thomas Mueller's avatar
Formatting fixes.
0f61802b
 
Thomas Mueller committed
517 
</li></ul>
buckyballs's avatar
Docs-Performance: JVM choice & Data Types
4c33d834
 
buckyballs committed
518
Thomas Mueller's avatar
docs
da30c87b
 
Thomas Mueller committed
519 
<h2 id="fast_import">Fast Database Import</h2>
Thomas Mueller's avatar
Improved docs.
27d7b7d3
 
Thomas Mueller committed
520 521 522 
<p>
To speed up large imports, consider using the following options temporarily:
</p>
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
523 524 525 526 
<ul><li><code>SET CACHE_SIZE</code> (a large cache is faster)
</li><li><code>SET LOCK_MODE 0</code> (disable locking)
</li><li><code>SET LOG 0</code> (disable the transaction log)
</li><li><code>SET UNDO_LOG 0</code> (disable the session undo log)
Thomas Mueller's avatar
Improved docs.
27d7b7d3
 
Thomas Mueller committed
527 528 529 
</li></ul>
<p>
These options can be set in the database URL:
Thomas Mueller's avatar
Documentation: improved website translation
20294dfb
 
Thomas Mueller committed
530 
<code>jdbc:h2:~/test;CACHE_SIZE=65536;LOCK_MODE=0;LOG=0;UNDO_LOG=0</code>.
Thomas Mueller's avatar
Improved docs.
27d7b7d3
 
Thomas Mueller committed
531 532 533 
Most of those options are not recommended for regular use, that means you need to reset them after use.
</p>
Thomas Mueller's avatar
use unix newline, no trailing spaces
1e7406b5
 
Thomas Mueller committed
534 
<!-- [close] { --></div></td></tr></table><!-- } --><!-- analytics --></body></html>