mirror of
https://github.com/yasuhirokimura/db18
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Yasuhiro KIMURA
191 lines
7.6 KiB
HTML
191 lines
7.6 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>Chapter 18. The Logging Subsystem</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="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="index.html" title="Berkeley DB Programmer's Reference Guide" />
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<link rel="prev" href="lock_nondb.html" title="Locking and non-Berkeley DB applications" />
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<link rel="next" href="log_config.html" title="Configuring logging" />
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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 18.1.40</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">Chapter 18. The Logging Subsystem </th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="lock_nondb.html">Prev</a> </td>
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<th width="60%" align="center"> </th>
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<td width="20%" align="right"> <a accesskey="n" href="log_config.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="chapter" 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"><a id="log"></a>Chapter 18. The Logging Subsystem </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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<p>
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<b>Table of Contents</b>
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</p>
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<dl>
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<dt>
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<span class="sect1">
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<a href="log.html#log_intro">Introduction to the logging
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subsystem</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="log_config.html">Configuring logging</a>
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</span>
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</dt>
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<dt>
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<span class="sect1">
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<a href="log_limits.html">Log file limits</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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<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="log_intro"></a>Introduction to the logging
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subsystem</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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The Logging subsystem is the logging facility used by
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Berkeley DB. It is largely Berkeley DB-specific, although it
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is potentially useful outside of the Berkeley DB package for
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applications wanting write-ahead logging support. Applications
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wanting to use the log for purposes other than logging file
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modifications based on a set of open file descriptors will
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almost certainly need to make source code modifications to the
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Berkeley DB code base.
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</p>
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<p>
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A log can be shared by any number of threads of control. The
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<a href="../api_reference/C/envopen.html" class="olink">DB_ENV->open()</a> method is used to open a log. When the log is no
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longer in use, it should be closed using the <a href="../api_reference/C/envclose.html" class="olink">DB_ENV->close()</a>
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method.
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</p>
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<p>
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Individual log entries are identified by log sequence
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numbers. Log sequence numbers are stored in an opaque object,
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an <a href="../api_reference/C/lsn.html" class="olink">DB_LSN</a>.
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</p>
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<p>
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The <a href="../api_reference/C/logcursor.html" class="olink">DB_ENV->log_cursor()</a> method is used to allocate a log cursor. Log
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cursors have two methods: <a href="../api_reference/C/logcget.html" class="olink">DB_LOGC->get()</a> method to retrieve log
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records from the log, and <a href="../api_reference/C/logcclose.html" class="olink">DB_LOGC->close()</a> method to destroy the
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cursor.
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</p>
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<p>
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There are additional methods for integrating the log
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subsystem with a transaction processing system:
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</p>
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<div class="variablelist">
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<dl>
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<dt>
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<span class="term">
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<a href="../api_reference/C/logflush.html" class="olink">DB_ENV->log_flush()</a>
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</span>
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</dt>
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<dd>
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Flushes the log up to a particular log sequence
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number.
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</dd>
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<dt>
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<span class="term">
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<a href="../api_reference/C/logcompare.html" class="olink">DB_ENV->log_compare()</a>
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</span>
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</dt>
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<dd>
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Allows applications to compare any two log
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sequence numbers.
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</dd>
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<dt>
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<span class="term">
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<a href="../api_reference/C/logfile.html" class="olink">DB_ENV->log_file()</a>
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</span>
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</dt>
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<dd>
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Maps a log sequence number to the specific log
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file that contains it.
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</dd>
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<dt>
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<span class="term">
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<a href="../api_reference/C/logarchive.html" class="olink">DB_ENV->log_archive()</a>
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</span>
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</dt>
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<dd>
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Returns various sets of log filenames. These
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methods are used for database administration; for
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example, to determine if log files may safely be
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removed from the system.
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</dd>
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<dt>
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<span class="term">
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<a href="../api_reference/C/logstat.html" class="olink">DB_ENV->log_stat()</a>
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</span>
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</dt>
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<dd>
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The display <a href="../api_reference/C/db_stat.html" class="olink">db_stat</a> utility used the <a href="../api_reference/C/logstat.html" class="olink">DB_ENV->log_stat()</a> method
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to display statistics about the log.
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</dd>
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<dt>
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<span class="term">
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<a href="../api_reference/C/envremove.html" class="olink">DB_ENV->remove()</a>
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</span>
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</dt>
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<dd>
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The log meta-information (but not the log files
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themselves) may be removed using the <a href="../api_reference/C/envremove.html" class="olink">DB_ENV->remove()</a>
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method.
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</dd>
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</dl>
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</div>
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<p>
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For more information on the logging subsystem methods, see
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the <a href="../api_reference/C/lsn.html#loglist" class="olink">Logging
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Subsystem and Related Methods</a> section in the
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<em class="citetitle">Berkeley DB C API Reference Guide.</em>
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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="lock_nondb.html">Prev</a> </td>
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<td width="20%" align="center"> </td>
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<td width="40%" align="right"> <a accesskey="n" href="log_config.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">Locking and non-Berkeley DB
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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"> Configuring logging</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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