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HTML
187 lines
8 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Managing the Background Threads</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Getting Started with Berkeley DB Java Edition" />
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<link rel="up" href="administration.html" title="Chapter 12. Administering Berkeley DB Java Edition Applications" />
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<link rel="prev" href="administration.html" title="Chapter 12. Administering Berkeley DB Java Edition Applications" />
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<link rel="next" href="cachesize.html" title="Sizing the Cache" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 12.2.7.5</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Managing the Background Threads</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="administration.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 12. Administering Berkeley DB Java Edition Applications</th>
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<td width="20%" align="right"> <a accesskey="n" href="cachesize.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="backgroundthreads"></a>Managing the Background Threads</h2>
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</div>
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</div>
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</div>
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<div class="toc">
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<dl>
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<dt>
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<span class="sect2">
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<a href="backgroundthreads.html#cleaner">The Cleaner Thread</a>
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</span>
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</dt>
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<dt>
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<span class="sect2">
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<a href="backgroundthreads.html#checkpointer">The Checkpointer Thread</a>
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</span>
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</dt>
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</dl>
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</div>
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<p>
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JE uses some background threads to keep your database resources within pre-configured limits. If they are
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going to run, the background threads are started once per application per process. That is, if your application
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opens the same environment multiple times, the background threads will be started just once for that process.
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See the following list for the default conditions that gate whether an individual thread is run. Note that you
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can prevent a background thread from running by using the appropriate <code class="filename">je.properties</code>
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parameter, but this is not recommended for production use and those parameters are not described here.
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</p>
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<p>
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The background threads are:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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Cleaner thread.
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</p>
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<p>
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Responsible for cleaning and deleting unused log files. See <a class="xref" href="backgroundthreads.html#cleaner" title="The Cleaner Thread">The Cleaner Thread</a> for more information.
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</p>
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<p>
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This thread is run only if the environment is opened for write access.
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</p>
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</li>
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<li>
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<p>
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Compressor thread.
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</p>
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<p>
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Responsible for cleaning up the internal BTree as database records are deleted. The compressor thread
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ensures that the BTree does not contain unused nodes. There is no need for you to manage the
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compressor and so it is not described further in this manual.
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</p>
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<p>
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This thread is run only if the environment is opened for write access.
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</p>
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</li>
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<li>
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<p>
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Checkpointer thread.
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</p>
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<p>
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Responsible for running checkpoints on your environment. See
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<a class="xref" href="backgroundthreads.html#checkpointer" title="The Checkpointer Thread">The Checkpointer Thread</a> for more information.
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</p>
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<p>
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This thread always runs.
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</p>
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</li>
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</ul>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="cleaner"></a>The Cleaner Thread</h3>
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</div>
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</div>
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</div>
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<p>
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The cleaner thread is responsible for cleaning, or compacting, your log files for you.
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Log file cleaning is described in <a class="xref" href="backuprestore.html#logcleaning" title="Cleaning the Log Files">Cleaning the Log Files</a>.
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</p>
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<p>
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The following two properties may be of interest to you when managing the cleaner thread:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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<code class="literal">je.cleaner.minUtilization</code>
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</p>
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<p>
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Identifies the percentage of the log file space that must be used for utilized records. If the
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percentage of log file space used by utilized records is too low, then the cleaner removes
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obsolete records until this threshold is reached. Default is 50%.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">je.cleaner.expunge</code>
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</p>
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<p>
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Identifies the cleaner's behavior in the event that it is able to remove a log file. If
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<code class="literal">true</code>, the log files that have been cleaned are deleted from the file system. If
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<code class="literal">false</code>, the log files that have been cleaned are renamed from
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<code class="literal">NNNNNNNN.jdb</code> to <code class="literal">NNNNNNNN.del</code>. You are then responsible for
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deleting the renamed files.
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</p>
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</li>
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</ul>
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</div>
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<p>
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Note that the cleaner thread runs only if the environment is opened for write access. Also, be aware that
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the cleaner is not guaranteed to finish running before the environment is closed, which can result in
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unexpectedly large log files. See
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<a class="xref" href="envclose.html" title="Closing Database Environments">Closing Database Environments</a> for more information.
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</p>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="checkpointer"></a>The Checkpointer Thread</h3>
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</div>
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</div>
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</div>
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<p>
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Automatically runs checkpoints. Checkpoints and the administration of this thread are described in
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the <em class="citetitle">Berkeley DB, Java Edition Getting Started with Transaction Processing</em> guide.
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</p>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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||
<table width="100%" summary="Navigation footer">
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||
<tr>
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||
<td width="40%" align="left"><a accesskey="p" href="administration.html">Prev</a> </td>
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||
<td width="20%" align="center">
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<a accesskey="u" href="administration.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="cachesize.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Chapter 12. Administering Berkeley DB Java Edition Applications </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Sizing the Cache</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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