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HTML
118 lines
5.9 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>Recovery and filesystem operations</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="transapp.html" title="Chapter 11. Berkeley DB Transactional Data Store Applications" />
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<link rel="prev" href="transapp_journal.html" title="Using Recovery on Journaling Filesystems" />
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<link rel="next" href="transapp_reclimit.html" title="Berkeley DB recoverability" />
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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 11.2.5.3</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">Recovery and filesystem operations</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="transapp_journal.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 11.
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Berkeley DB Transactional Data Store Applications
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="transapp_reclimit.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="transapp_filesys"></a>Recovery and filesystem operations</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 Berkeley DB API supports creating, removing and renaming files.
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Creating files is supported by the <a href="../api_reference/C/dbopen.html" class="olink">DB->open()</a> method. Removing files is
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supported by the <a href="../api_reference/C/envdbremove.html" class="olink">DB_ENV->dbremove()</a> and <a href="../api_reference/C/dbremove.html" class="olink">DB->remove()</a> methods. Renaming files
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is supported by the <a href="../api_reference/C/envdbrename.html" class="olink">DB_ENV->dbrename()</a> and <a href="../api_reference/C/dbrename.html" class="olink">DB->rename()</a> methods. (There are
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two methods for removing and renaming files because one of the methods
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is transactionally protected and one is not.)
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</p>
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<p>
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Berkeley DB does not permit specifying the <a href="../api_reference/C/dbopen.html#open_DB_TRUNCATE" class="olink">DB_TRUNCATE</a> flag when
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opening a file in a transaction-protected environment. This is an
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implicit file deletion, but one that does not always require the same
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operating system file permissions as deleting and creating a file do.
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</p>
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<p>
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If you have changed the name of a file or deleted it outside of the
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Berkeley DB library (for example, you explicitly removed a file using
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your normal operating system utilities), then it is possible that
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recovery will not be able to find a database to which the log refers.
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In this case, the <a href="../api_reference/C/db_recover.html" class="olink">db_recover</a> utility will produce a warning message, saying
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it was unable to locate a file it expected to find. This message is
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only a warning because the file may have been subsequently deleted as
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part of normal database operations before the failure occurred, so is
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not necessarily a problem.
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</p>
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<p>
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Generally, any filesystem operations that are performed outside the
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Berkeley DB interface should be performed at the same time as making a
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snapshot of the database. To perform filesystem operations correctly,
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do the following:
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</p>
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<div class="orderedlist">
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<ol type="1">
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<li>
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<p>Cleanly shut down database operations.</p>
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<p>To shut down database operations cleanly, all applications accessing
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the database environment must be shut down and a transaction checkpoint
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must be taken. If the applications are not implemented so they can be
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shut down gracefully (that is, closing all references to the database
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environment), recovery must be performed after all applications have
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been killed to ensure that the underlying databases are consistent on
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disk.</p>
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</li>
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<li>Perform the filesystem operations; for example, remove or rename one or
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more files.</li>
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<li>
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<p>Make an archival snapshot of the database.</p>
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<p>Although this step is not strictly necessary, it is strongly
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recommended. If this step is not performed, recovery from catastrophic
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failure will require that recovery first be performed up to the time of
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the filesystem operations, the filesystem operations be redone, and then
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recovery be performed from the filesystem operations forward.</p>
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</li>
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<li>Restart the database applications.</li>
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</ol>
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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="transapp_journal.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="transapp.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="transapp_reclimit.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">Using Recovery on Journaling Filesystems </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"> Berkeley DB recoverability</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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