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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>Restoring Log Files</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 High Availability Applications" />
<link rel="up" href="utilities.html" title="Chapter 4. Utilities" />
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<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">Restoring Log Files</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="utilities.html">Prev</a> </td>
<th width="60%" align="center">Chapter 4. Utilities</th>
<td width="20%" align="right"> <a accesskey="n" href="dbbackup.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="logfile-restore"></a>Restoring Log Files</h2>
</div>
</div>
</div>
<div class="toc">
<dl>
<dt>
<span class="sect2">
<a href="logfile-restore.html#logfilereclaim">Reclaiming Log Files</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="logfile-restore.html#repdiskthresh">Suspending Writes Due to Disk Thresholds</a>
</span>
</dt>
</dl>
</div>
<p>
During normal operations, the nodes in a replication group
communicate with one another to ensure that the JE cleaner
does not reclaim log files still needed by the group. The tail
end of the replication stream may still be needed by a lagging
Replica in order to make it current with the Master, and so the
replication group tries to make sure the trailing log files needed to
bring lagging Replicas up-to-date are not reclaimed.
</p>
<p>
However, if a node is unavailable for a long enough period
of time, then log files needed to bring it up to date might
have been reclaimed by the cleaner.
For information on how and when log files are reclaimed in
a replicated environment, see
<a class="xref" href="logfile-restore.html#logfilereclaim" title="Reclaiming Log Files">Reclaiming Log Files</a>.
</p>
<p>
Once log files have been reclaimed by a cleaner, then the
Replica can no longer be brought up to date using the normal
replication stream. Your application code will know this has
happened when the <a class="ulink" href="../java/com/sleepycat/je/rep/ReplicatedEnvironment.html" target="_top">ReplicatedEnvironment</a> constructor throws
an <a class="ulink" href="../java/com/sleepycat/je/rep/InsufficientLogException.html" target="_top">InsufficientLogException</a>.
</p>
<p>
When your code catches an <a class="ulink" href="../java/com/sleepycat/je/rep/InsufficientLogException.html" target="_top">InsufficientLogException</a>, then you
must bring the Replica up-to-date using a mechanism other than
the normal replication stream. You do this using the
<a class="ulink" href="../java/com/sleepycat/je/rep/NetworkRestore.html" target="_top">NetworkRestore</a> class. A call to <a class="ulink" href="../java/com/sleepycat/je/rep/NetworkRestore.html#execute(com.sleepycate.je.rep.InsufficientLogException,com.sleepycat.je.rep.NetworkRestoreConfig)" target="_top">NetworkRestore.execute()</a>
causes the Replica to copy the missing log files from a member
of the replication group who owns the files and seems to be the
least busy. Once the Replica has obtained the log files that it
requires, it automatically re-establishes its replication stream
with the Master so that the Master can finish bringing the
Replica up-to-date.
</p>
<p>
For example:
</p>
<pre class="programlisting"> ...
try {
node = new ReplicatedEnvironment(envDir, repConfig, envConfig);
} catch (InsufficientLogException insufficientLogEx) {
NetworkRestore restore = new NetworkRestore();
NetworkRestoreConfig config = new NetworkRestoreConfig();
config.setRetainLogFiles(false); // delete obsolete log files.
// Use the members returned by insufficientLogEx.getLogProviders()
// to select the desired subset of members and pass the resulting
// list as the argument to config.setLogProviders(), if the
// default selection of providers is not suitable.
restore.execute(insufficientLogEx, config);
// retry
node = new ReplicatedEnvironment(envDir, repConfig, envConfig);
} ... </pre>
<p>
Note that the replication group does not maintain information
about the log files needed by secondary nodes. Instead, the
system retains a set of log files beyond those required for a
network restore based on the <a class="ulink" href="../java/com/sleepycat/je/rep/ReplicationConfig.html#NETWORK_RESTORE_OVERHEAD" target="_top">NETWORK_RESTORE_OVERHEAD</a> property,
which you can manage using <a class="ulink" href="../java/com/sleepycat/je/rep/ReplicationConfig.html#setConfigParam(java.lang.String,java.lang.String)" target="_top">ReplicationConfig.setConfigParam()</a>.
The default value is 10, which means that the system uses the
estimate of 10 percent for the additional amount of data that
performing a network restore needs to send over the network as
compared to using the same log files to perform replication. In
this case, the system saves files containing an additional 10
percent of log data beyond the amount needed for a network
restore.
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="logfilereclaim"></a>Reclaiming Log Files</h3>
</div>
</div>
</div>
<p>
Ordinarily JE's cleaner thread reclaims log files as soon as possible
so as to minimize the amount of disk space used by the database. Log files
are reclaimed as records are deleted, and log files are subsequently compacted.
</p>
<p>
However, various database activities might cause log files
to be temporarily reserved or protected temporarily. A
<span class="emphasis"><em>reserved file</em></span> is a file that JE
can delete but has yet done so. A
<span class="emphasis"><em>protected file</em></span> is a file that should
be deleted, but JE cannot do so due to some database
activity, such as a backup.
</p>
<p>
For replicated environments, JE hangs on to log files as long
as possible in case they are needed to bring a replica up to date. Log
files that have been cleaned but then saved due because of replication
are in a <span class="emphasis"><em>reserved</em></span> state. All such files are
retained until the disk usage thresholds as defined by <a class="ulink" href="../java/com/sleepycat/je/EnvironmentConfig.html#MAX_DISK" target="_top">EnvironmentConfig.MAX_DISK</a>
and <a class="ulink" href="../java/com/sleepycat/je/EnvironmentConfig.html#FREE_DISK" target="_top">EnvironmentConfig.FREE_DISK</a> are exceeded. At that point, JE deletes reserved
log files.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="repdiskthresh"></a>Suspending Writes Due to Disk Thresholds</h3>
</div>
</div>
</div>
<p>
In the previous section, we mentioned that JE reserves
cleaned log files until disk threshold limits are encountered,
at which time log files are reclaimed (deleted).
</p>
<p>
Be aware that if reclaiming log files does not allow JE
to meet its disk usage threshold limits, then writes are
disabled for one or more nodes in the replication group.
</p>
<p>
If the threshold limits cannot be met on the Master, then
write operations will throw <a class="ulink" href="../java/com/sleepycat/je/DiskLimitException.html" target="_top">DiskLimitException</a> just as
they would for a non-replicated environment.
</p>
<p>
If the threshold limit cannot be met on a replica, then
writes are disabled only on that replica. In this case, the
Master might see <a class="ulink" href="../java/com/sleepycat/je/rep/InsufficientAcksException.html" target="_top">InsufficientAcksException</a> thrown in
response to a write — if your application's
durability guarantee cannot be met due to the replica being
unable to perform writes.
</p>
</div>
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