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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Performing Backups</title>
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
<link rel="start" href="index.html" title="Getting Started with Berkeley DB Java Edition" />
<link rel="up" href="backuprestore.html" title="Chapter 11. Backing up and Restoring Berkeley DB Java Edition Applications" />
<link rel="prev" href="backuprestore.html" title="Chapter 11. Backing up and Restoring Berkeley DB Java Edition Applications" />
<link rel="next" href="catastrophicrecovery.html" title="Performing Catastrophic Recovery" />
</head>
<body>
<div xmlns="" class="navheader">
<div class="libver">
<p>Library Version 12.2.7.5</p>
</div>
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">Performing Backups</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="backuprestore.html">Prev</a> </td>
<th width="60%" align="center">Chapter 11. Backing up and Restoring Berkeley DB Java Edition Applications</th>
<td width="20%" align="right"> <a accesskey="n" href="catastrophicrecovery.html">Next</a></td>
</tr>
</table>
<hr />
</div>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="backup"></a>Performing Backups</h2>
</div>
</div>
</div>
<div class="toc">
<dl>
<dt>
<span class="sect2">
<a href="backup.html#partialBackup">Performing a Hot Backup</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="backup.html#completeBackup">Performing an Offline Backup</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="backup.html#dbbackuphelper">Using the DbBackup Helper Class</a>
</span>
</dt>
</dl>
</div>
<p>
This section describes how to backup your JE database(s) such that catastrophic recovery is possible for
non-transactional applications. Note that this same material is repeated in the
<em class="citetitle">Berkeley DB, Java Edition Getting Started with Transaction Processing</em>
guide, but for transactional applications. If you are writing transactional
applications, you may want to skip the rest of this chapter and go straight to that book.
</p>
<p>
To backup your database, you can either take a hot backup or an offline backup. A hot
backup is performed while database write operations are in progress.
</p>
<p>
Do not confuse hot and offline backups with the concept of a full and incremental backup. Both a
hot and an offline backup are full backups – you back up the entire database. The only difference
between them is how much of the contents of the in-memory cache are contained in them. On the other hand,
an incremental backup is a backup of just those log files modified or created since the time of the last
backup. Most backup software
is capable of performing both full and incremental backups for you.
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="partialBackup"></a>Performing a Hot Backup</h3>
</div>
</div>
</div>
<p>
To perform a hot backup of your JE databases, copy all log files
(<code class="filename">*.jdb</code> files) from your environment directory to
your archival location or backup media. The files must be copied
in alphabetical order (numerical in effect). You do not have to
stop any database operations in order to do this.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
If you are using subdirectories to store your log files, then you must backup
the subdirectories, making sure to keep log files in the subdirectory in which
JE placed them. For information on using subdirectories to store your log
files, see <a class="xref" href="env.html#multisubdir" title="Multiple Environment Subdirectories">Multiple Environment Subdirectories</a>.
</p>
</div>
<p>
To make this process a bit easier, you may want to make use of the
<code class="classname">DbBackup</code> helper class. See
<a class="xref" href="backup.html#dbbackuphelper" title="Using the DbBackup Helper Class">Using the DbBackup Helper Class</a>
for details.
</p>
<p>
Note that any modifications made to the database since the time of the last
environment sync are not guaranteed to be contained in these log files. In this
case, you may want to consider running an offline backup in order to guarantee the
availability of all modifications made to your database.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="completeBackup"></a>Performing an Offline Backup</h3>
</div>
</div>
</div>
<p>
An offline backup guarantees that you have captured the database in its entirety, including all contents
of your in-memory cache, at the moment that the
backup was taken. To do this, you must make sure that no write operations are in progress and all
database modifications have been written to your log files
on disk. To obtain an offline backup:
</p>
<div class="orderedlist">
<ol type="1">
<li>
<p>
Stop writing your databases.
</p>
</li>
<li>
<p>
Run <code class="methodname">Environment.sync()</code> so as to
ensure that all database modifications are written to disk. Note that cleanly closing your
environment will also ensure that all database modifications are written to disk.
</p>
</li>
<li>
<p>
Copy all log files (<code class="filename">*.jdb</code>) from your environment
directory to your archival location or backup media. To make this process a
bit easier, you may want to make use of the <code class="classname">DbBackup</code>
helper class. See the next section for details.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
If you are using subdirectories to store your log files, then you must backup
the subdirectories, making sure to keep log files in the subdirectory in which
JE placed them. For information on using subdirectories to store your log
files, see <a class="xref" href="env.html#multisubdir" title="Multiple Environment Subdirectories">Multiple Environment Subdirectories</a>.
</p>
</div>
</li>
</ol>
</div>
<p>
You can now resume normal database operations.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="dbbackuphelper"></a>Using the DbBackup Helper Class</h3>
</div>
</div>
</div>
<p>
In order to simplify backup operations, JE
provides the <code class="classname">DbBackup</code> helper
class. This class stops and restarts JE background activity
in an open environment. It also lets the application create a
backup which can support restoring the environment to
a specific point in time.
</p>
<p>
Because you do not have to stop JE write activity
in order to take a backup, it is usually necessary to
examine your log files twice before you decide that
your backup is complete. This is because JE may
create a new log file while you are running your
backup. A second pass over your log files allows you to
ensure that no new files have been created and so you
can declare your backup complete.
</p>
<p>
For example:
</p>
<pre class="programlisting"> time files in activity
environment
t0 000000001.jdb Backup starts copying file 1
000000003.jdb
000000004.jdb
t1 000000001.jdb JE log cleaner migrates portion of file 3 to
000000004.jdb newly created file 5 and deletes file 3.
000000005.jdb Backup finishes file 1, starts copying file 4.
Backup MUST include file 5 for a consistent
backup!
t2 000000001.jdb Backup finishes copying file 4, starts and
000000004.jdb finishes file 5, has caught up. Backup ends.
000000005.jdb
</pre>
<p>
<code class="classname">DbBackup</code> works around this
problem by defining the set of files that must be
copied for each backup operation, and freezes all
changes to those files. The application can copy that
defined set of files and finish operation without
checking for the ongoing creation of new files. Also,
there will be no need to check for a newer version of
the last file on the next backup.
</p>
<p>
In the example above, if <code class="classname">DbBackup</code> was used at t0,
the application would only have to copy files 1, 3 and
4 to back up. On a subsequent backup, the application
could start its copying at file 5. There would be no
need to check for a newer version of file 4.
</p>
<p>
The following code fragment illustrates this class' usage.
See the <code class="classname">DbBackup</code> javadoc for additional
examples and more information on incremental backups.
</p>
<pre class="programlisting">package je.gettingStarted;
...
import com.sleepycat.je.util.DbBackup;
...
// Find the file number of the last file in the previous backup
// persistently, by either checking the backup archive, or saving
// state in a persistent file.
long lastFileCopiedInPrevBackup = ...
Environment env = new Environment(...);
DbBackup backupHelper = new DbBackup(env, lastFileCopiedInPrevBackup);
// Start backup, find out what needs to be copied.
// If multiple environment subdirectories are in use,
// the getLogFilesInBackupSet returns the log file
// name prefixed with the dataNNN/ directory in which
// it resides.
backupHelper.startBackup();
try {
String[] filesForBackup = backupHelper.getLogFilesInBackupSet();
// Copy the files to archival storage.
myApplicationCopyMethod(filesForBackup)
// Update our knowlege of the last file saved in the backup set,
// so we can copy less on the next backup
lastFileCopiedInPrevBackup = backupHelper.getLastFileInBackupSet();
myApplicationSaveLastFile(lastFileCopiedInBackupSet);
}
finally {
// Remember to exit backup mode, or all log files won't be cleaned
// and disk usage will bloat.
backupHelper.endBackup();
} </pre>
</div>
</div>
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<hr />
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<td width="40%" align="left"><a accesskey="p" href="backuprestore.html">Prev</a> </td>
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<a accesskey="u" href="backuprestore.html">Up</a>
</td>
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</tr>
<tr>
<td width="40%" align="left" valign="top">Chapter 11. Backing up and Restoring Berkeley DB Java Edition Applications </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
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</tr>
</table>
</div>
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