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89 lines
4.9 KiB
HTML
89 lines
4.9 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>Checkpoints</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 Transaction Processing" />
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<link rel="up" href="jebackuprestore.html" title="Chapter 5. Backing up and Restoring Berkeley DB, Java Edition Applications" />
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<link rel="prev" href="jebackuprestore.html" title="Chapter 5. Backing up and Restoring Berkeley DB, Java Edition Applications" />
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<link rel="next" href="backup.html" title="Performing Backups" />
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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">Checkpoints</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="jebackuprestore.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 5. Backing up and Restoring Berkeley DB, Java Edition Applications</th>
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<td width="20%" align="right"> <a accesskey="n" href="backup.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="chkpoint"></a>Checkpoints</h2>
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</div>
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</div>
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</div>
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<p>
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Running normal recovery can become expensive if over time all that is ever
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written to disk is BTree leaf nodes. So in order to limit the time required for normal recovery, JE runs
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checkpoints. Checkpoints write to your log files all the internal BTree nodes and structures modified as a part of
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write operations. This means that your log files contain a complete BTree up to
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the moment in time when the checkpoint was run. The result is that normal recovery only needs to recreate the
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portion of the BTree that has been modified since the time of the last checkpoint.
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</p>
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<p>
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Checkpoints typically write more information to disk than do transaction commits, and so they are more
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expensive from a disk I/O perspective. You will therefore need to consider how frequently to run checkpoints
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as a part of your performance tuning activities. When you do this, balance the cost of the checkpoints
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against the time it will take your application to restart due to the cost of running normal recovery.
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</p>
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<p>
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Checkpoints are normally performed by the checkpointer background thread, which is always running. Like
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all background threads, it is managed using the <code class="filename">je.properties</code> file. Currently, the
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only checkpointer property that you may want to manage is
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<code class="literal">je.checkpointer.bytesInterval</code>. This property identifies how much JE's log files
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can grow before a checkpoint is run. Its value is specified in bytes. Decreasing this value causes the
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checkpointer thread to run checkpoints more frequently. This will improve the time that it takes to run
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recovery, but it also increases the system resources (notably, I/O) required by JE.
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</p>
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<p>
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Note that checkpoints are also always performed when the environment is closed normally. Therefore,
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normal recovery only has work to do if the application crashes or otherwise ends abnormally without
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calling <code class="methodname">Environment.close()</code>.
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</p>
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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="jebackuprestore.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="jebackuprestore.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="backup.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 5. Backing up and Restoring 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"> Performing Backups</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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