mirror of
https://github.com/berkeleydb/je.git
synced 2024-09-09 03:56:13 +00:00
131 lines
6.9 KiB
HTML
131 lines
6.9 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
|
||
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
||
<html xmlns="http://www.w3.org/1999/xhtml">
|
||
<head>
|
||
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
|
||
<title>Sizing the Cache</title>
|
||
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
|
||
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
|
||
<link rel="start" href="index.html" title="Getting Started with Berkeley DB Java Edition" />
|
||
<link rel="up" href="administration.html" title="Chapter 12. Administering Berkeley DB Java Edition Applications" />
|
||
<link rel="prev" href="backgroundthreads.html" title="Managing the Background Threads" />
|
||
<link rel="next" href="diskthreshold.html" title="Setting Disk Thresholds" />
|
||
</head>
|
||
<body>
|
||
<div xmlns="" class="navheader">
|
||
<div class="libver">
|
||
<p>Library Version 12.2.7.5</p>
|
||
</div>
|
||
<table width="100%" summary="Navigation header">
|
||
<tr>
|
||
<th colspan="3" align="center">Sizing the Cache</th>
|
||
</tr>
|
||
<tr>
|
||
<td width="20%" align="left"><a accesskey="p" href="backgroundthreads.html">Prev</a> </td>
|
||
<th width="60%" align="center">Chapter 12. Administering Berkeley DB Java Edition Applications</th>
|
||
<td width="20%" align="right"> <a accesskey="n" href="diskthreshold.html">Next</a></td>
|
||
</tr>
|
||
</table>
|
||
<hr />
|
||
</div>
|
||
<div class="sect1" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h2 class="title" style="clear: both"><a id="cachesize"></a>Sizing the Cache</h2>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>
|
||
By default, your cache is limited to a percentage of the JVM maximum
|
||
memory as specified by the <code class="literal">-Xmx</code> parameter. You can
|
||
change this percentage by using the <code class="literal">je.maxMemoryPercent</code> property
|
||
or through <code class="methodname">EnvironmentMutableConfig.setCachePercent()</code>.
|
||
That is, the maximum amount of memory available to your cache is
|
||
normally calculated as:
|
||
</p>
|
||
<pre class="programlisting">je.maxMemoryPercent * JVM_maximum_memory</pre>
|
||
<p>
|
||
You can find out what the value for this property is by using
|
||
<code class="methodname">EnvironmentConfig.getCachePercent()</code>.
|
||
</p>
|
||
<p>
|
||
Note that you can cause JE to use a fixed maximum cache size by
|
||
using <code class="literal">je.maxMemory</code> or by using
|
||
<code class="methodname">EnvironmentConfig.setCacheSize()</code>.
|
||
</p>
|
||
<p>
|
||
Also, not every JVM is capable of identifying the amount of memory requested via
|
||
the <code class="literal">-Xmx</code> parameter. For those JVMs you must use
|
||
<code class="literal">je.maxMemory</code> to change your maximum cache size. The
|
||
default maximum memory available to your cache in this case is 38M.
|
||
</p>
|
||
<p>
|
||
Of the amount of memory allowed for your cache, 93% is used for the internal BTree and the other 7% is
|
||
used for internal buffers. When your application first starts up, the 7% for buffers is immediately allocated.
|
||
The remainder of the cache grows lazily as your application reads and writes data.
|
||
</p>
|
||
<p>
|
||
In order for your application to start up successfully, the Java virtual machine must have enough memory
|
||
available to it (as identified by the <code class="literal">-Xmx</code> command line switch) for both your application and
|
||
7% of your maximum cache value. In order for your application to run continuously (all the while loading data
|
||
into the cache), you must make sure your JVM has enough memory for your application plus the maximum cache size.
|
||
</p>
|
||
<p>
|
||
The best way to determine how large your cache needs to be is to put your application into a production
|
||
environment and watch to see how much disk I/O is occurring. If the application is going to disk quite a lot to
|
||
retrieve database records, then you should increase the size of your cache (provided that you have enough memory
|
||
to do so).
|
||
</p>
|
||
<p>
|
||
You can also use the
|
||
<code class="methodname">com.sleepycat.je.util.DbCacheSize</code> utility
|
||
to obtain a rough estimate of how large your cache needs to be for
|
||
a given number of records and record characteristics. The utility
|
||
returns an estimate of the cache size to hold
|
||
the specified number of records in memory. See the
|
||
<a class="ulink" href="../java/com/sleepycat/je/util/DbCacheSize.html" target="_top">DbCacheSize javadoc</a>
|
||
for information on the utility's usage.
|
||
</p>
|
||
<p>
|
||
In order to determine how frequently your application is going to disk for database records not found in the
|
||
cache, you can examine the value returned by <code class="methodname">EnvironmentStats.getNCacheMiss()</code>.
|
||
</p>
|
||
<p>
|
||
<code class="methodname">EnvironmentStats.getNCacheMiss()</code> identifies the total number of requests for
|
||
database objects that were
|
||
not serviceable from the cache. This value is cumulative since the application started. The faster this number grows,
|
||
the more your application is going to disk to service database operations. Upon application startup you can
|
||
expect this value to grow quite rapidly. However, as time passes and your cache is seeded with your most
|
||
frequently accessed database records, what you want is for this number's growth to be zero or at least very
|
||
small.
|
||
</p>
|
||
<p>
|
||
Note that this statistic can only be collected from within the application itself or using the JMX extension
|
||
(see <a class="xref" href="jmx.html" title="JConsole and JMX Support">JConsole and JMX Support</a>).
|
||
</p>
|
||
<p>
|
||
For more information on collecting this statistic, see <a class="xref" href="envStats.html" title="Environment Statistics">Environment Statistics</a>.
|
||
</p>
|
||
</div>
|
||
<div class="navfooter">
|
||
<hr />
|
||
<table width="100%" summary="Navigation footer">
|
||
<tr>
|
||
<td width="40%" align="left"><a accesskey="p" href="backgroundthreads.html">Prev</a> </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="u" href="administration.html">Up</a>
|
||
</td>
|
||
<td width="40%" align="right"> <a accesskey="n" href="diskthreshold.html">Next</a></td>
|
||
</tr>
|
||
<tr>
|
||
<td width="40%" align="left" valign="top">Managing the Background Threads </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="h" href="index.html">Home</a>
|
||
</td>
|
||
<td width="40%" align="right" valign="top"> Setting Disk Thresholds</td>
|
||
</tr>
|
||
</table>
|
||
</div>
|
||
</body>
|
||
</html>
|