1<!--$Id: hotfail.so,v 10.5 2005/02/10 20:02:41 bostic Exp $--> 2<!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> 3<!--See the file LICENSE for redistribution information.--> 4<html> 5<head> 6<title>Berkeley DB Reference Guide: Hot failover</title> 7<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> 8<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> 9</head> 10<body bgcolor=white> 11<a name="2"><!--meow--></a> 12<table width="100%"><tr valign=top> 13<td><b><dl><dt>Berkeley DB Reference Guide:<dd>Berkeley DB Transactional Data Store Applications</dl></b></td> 14<td align=right><a href="/transapp/recovery.html"><img src="/images/prev.gif" alt="Prev"></a><a href="/toc.html"><img src="/images/ref.gif" alt="Ref"></a><a href="/transapp/filesys.html"><img src="/images/next.gif" alt="Next"></a> 15</td></tr></table> 16<p align=center><b>Hot failover</b></p> 17<p>For some applications, it may be useful to periodically snapshot the 18database environment for use as a hot failover should the primary system 19fail. The following steps can be taken to keep a backup environment in 20close synchrony with an active environment. The active environment is 21entirely unaffected by these procedures, and both read and write 22operations are allowed during all steps described here.</p> 23<ol> 24<p><li>Run <a href="/utility/db_archive.html">db_archive</a> <b>-s</b> in the active environment to 25identify all of the active environment's database files, and copy them 26to the backup directory. 27<p>If the database files are stored in a separate directory from the other 28Berkeley DB files, it will be simpler (and much faster!) to copy the directory 29itself instead of the individual files (see <a href="/api_c/env_set_data_dir.html">DB_ENV->set_data_dir</a> 30for additional information). <b>Note: if any of the database 31files did not have an open <a href="/api_c/db_class.html">DB</a> handle during the lifetime of the 32current log files, <a href="/utility/db_archive.html">db_archive</a> will not list them in its 33output!</b> This is another reason it may be simpler to use a separate 34database file directory and copy the entire directory instead of 35archiving only the files listed by <a href="/utility/db_archive.html">db_archive</a>.</p> 36<p><li>Remove all existing log files from the backup directory. 37<p><li>Run <a href="/utility/db_archive.html">db_archive</a> <b>-l</b> in the active environment to 38identify all of the active environment's log files, and copy them to 39the backup directory. 40<p><li>Run <a href="/utility/db_recover.html">db_recover</a> <b>-c</b> in the backup directory to 41catastrophically recover the copied environment. 42</ol> 43<p>Steps 2, 3 and 4 may be repeated as often as you like. If Step 1 (the 44initial copy of the database files) is repeated, then Steps 2, 3 and 4 45<b>must</b> be performed at least once in order to ensure a consistent 46database environment snapshot.</p> 47<p>These procedures must be integrated with your other archival procedures, 48of course. If you are periodically removing log files from your active 49environment, you must be sure to copy them to the backup directory 50before removing them from the active directory. Not copying a log file 51to the backup directory and subsequently running recovery with it 52present may leave the backup snapshot of the environment corrupted. A 53simple way to ensure this never happens is to archive the log files in 54Step 2 as you remove them from the backup directory, and move inactive 55log files from your active environment into your backup directory 56(rather than copying them), in Step 3. The following steps describe 57this procedure in more detail:</p> 58<ol> 59<p><li>Run <a href="/utility/db_archive.html">db_archive</a> <b>-s</b> in the active environment to 60identify all of the active environment's database files, and copy them 61to the backup directory. 62<p><li>Archive all existing log files from the backup directory, moving them 63to a backup device such as CD-ROM, alternate disk, or tape. 64<p><li>Run <a href="/utility/db_archive.html">db_archive</a> (without any option) in the active environment 65to identify all of the log files in the active environment that are no 66longer in use, and <b>move</b> them to the backup directory. 67<p><li>Run <a href="/utility/db_archive.html">db_archive</a> <b>-l</b> in the active environment to 68identify all of the remaining log files in the active environment, and 69<b>copy</b> the log files to the backup directory. 70<p><li>Run <a href="/utility/db_recover.html">db_recover</a> <b>-c</b> in the backup directory to 71catastrophically recover the copied environment. 72</ol> 73<p>As before, steps 2, 3, 4 and 5 may be repeated as often as you like. 74If Step 1 (the initial copy of the database files) is repeated, then 75Steps 2 through 5 <b>must</b> be performed at least once in order to 76ensure a consistent database environment snapshot.</p> 77<p>For an example of a hot backup implementation in the Berkeley DB distribution, 78see the source code for the <a href="/utility/db_hotbackup.html">db_hotbackup</a> utility.</p> 79<table width="100%"><tr><td><br></td><td align=right><a href="/transapp/recovery.html"><img src="/images/prev.gif" alt="Prev"></a><a href="/toc.html"><img src="/images/ref.gif" alt="Ref"></a><a href="/transapp/filesys.html"><img src="/images/next.gif" alt="Next"></a> 80</td></tr></table> 81<p><font size=1>Copyright (c) 1996,2008 Oracle. 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