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210 lines
11 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>Restoring Log Files</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="Getting Started with Berkeley DB, Java Edition High Availability Applications" />
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<link rel="up" href="utilities.html" title="Chapter 4. Utilities" />
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<link rel="prev" href="utilities.html" title="Chapter 4. Utilities" />
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<link rel="next" href="dbbackup.html" title="Backing up a Replicated Application" />
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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 12.2.7.5</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">Restoring Log Files</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="utilities.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 4. Utilities</th>
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<td width="20%" align="right"> <a accesskey="n" href="dbbackup.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="logfile-restore"></a>Restoring Log Files</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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<dl>
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<dt>
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<span class="sect2">
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<a href="logfile-restore.html#logfilereclaim">Reclaiming Log Files</a>
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</span>
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</dt>
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<dt>
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<span class="sect2">
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<a href="logfile-restore.html#repdiskthresh">Suspending Writes Due to Disk Thresholds</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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<p>
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During normal operations, the nodes in a replication group
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communicate with one another to ensure that the JE cleaner
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does not reclaim log files still needed by the group. The tail
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end of the replication stream may still be needed by a lagging
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Replica in order to make it current with the Master, and so the
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replication group tries to make sure the trailing log files needed to
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bring lagging Replicas up-to-date are not reclaimed.
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</p>
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<p>
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However, if a node is unavailable for a long enough period
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of time, then log files needed to bring it up to date might
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have been reclaimed by the cleaner.
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For information on how and when log files are reclaimed in
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a replicated environment, see
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<a class="xref" href="logfile-restore.html#logfilereclaim" title="Reclaiming Log Files">Reclaiming Log Files</a>.
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</p>
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<p>
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Once log files have been reclaimed by a cleaner, then the
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Replica can no longer be brought up to date using the normal
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replication stream. Your application code will know this has
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happened when the <a class="ulink" href="../java/com/sleepycat/je/rep/ReplicatedEnvironment.html" target="_top">ReplicatedEnvironment</a> constructor throws
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an <a class="ulink" href="../java/com/sleepycat/je/rep/InsufficientLogException.html" target="_top">InsufficientLogException</a>.
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</p>
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<p>
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When your code catches an <a class="ulink" href="../java/com/sleepycat/je/rep/InsufficientLogException.html" target="_top">InsufficientLogException</a>, then you
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must bring the Replica up-to-date using a mechanism other than
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the normal replication stream. You do this using the
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<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>
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causes the Replica to copy the missing log files from a member
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of the replication group who owns the files and seems to be the
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least busy. Once the Replica has obtained the log files that it
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requires, it automatically re-establishes its replication stream
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with the Master so that the Master can finish bringing the
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Replica up-to-date.
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</p>
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<p>
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For example:
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</p>
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<pre class="programlisting"> ...
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try {
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node = new ReplicatedEnvironment(envDir, repConfig, envConfig);
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} catch (InsufficientLogException insufficientLogEx) {
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NetworkRestore restore = new NetworkRestore();
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NetworkRestoreConfig config = new NetworkRestoreConfig();
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config.setRetainLogFiles(false); // delete obsolete log files.
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// Use the members returned by insufficientLogEx.getLogProviders()
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// to select the desired subset of members and pass the resulting
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// list as the argument to config.setLogProviders(), if the
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// default selection of providers is not suitable.
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restore.execute(insufficientLogEx, config);
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// retry
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node = new ReplicatedEnvironment(envDir, repConfig, envConfig);
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} ... </pre>
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<p>
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Note that the replication group does not maintain information
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about the log files needed by secondary nodes. Instead, the
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system retains a set of log files beyond those required for a
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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,
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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>.
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The default value is 10, which means that the system uses the
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estimate of 10 percent for the additional amount of data that
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performing a network restore needs to send over the network as
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compared to using the same log files to perform replication. In
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this case, the system saves files containing an additional 10
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percent of log data beyond the amount needed for a network
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restore.
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</p>
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<div class="sect2" 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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<h3 class="title"><a id="logfilereclaim"></a>Reclaiming Log Files</h3>
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</div>
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</div>
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</div>
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<p>
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Ordinarily JE's cleaner thread reclaims log files as soon as possible
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so as to minimize the amount of disk space used by the database. Log files
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are reclaimed as records are deleted, and log files are subsequently compacted.
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</p>
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<p>
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However, various database activities might cause log files
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to be temporarily reserved or protected temporarily. A
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<span class="emphasis"><em>reserved file</em></span> is a file that JE
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can delete but has yet done so. A
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<span class="emphasis"><em>protected file</em></span> is a file that should
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be deleted, but JE cannot do so due to some database
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activity, such as a backup.
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</p>
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<p>
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For replicated environments, JE hangs on to log files as long
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as possible in case they are needed to bring a replica up to date. Log
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files that have been cleaned but then saved due because of replication
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are in a <span class="emphasis"><em>reserved</em></span> state. All such files are
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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>
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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
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log files.
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</p>
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</div>
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<div class="sect2" 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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<h3 class="title"><a id="repdiskthresh"></a>Suspending Writes Due to Disk Thresholds</h3>
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</div>
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</div>
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</div>
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<p>
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In the previous section, we mentioned that JE reserves
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cleaned log files until disk threshold limits are encountered,
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at which time log files are reclaimed (deleted).
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</p>
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<p>
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Be aware that if reclaiming log files does not allow JE
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to meet its disk usage threshold limits, then writes are
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disabled for one or more nodes in the replication group.
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</p>
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<p>
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If the threshold limits cannot be met on the Master, then
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write operations will throw <a class="ulink" href="../java/com/sleepycat/je/DiskLimitException.html" target="_top">DiskLimitException</a> just as
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they would for a non-replicated environment.
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</p>
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<p>
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If the threshold limit cannot be met on a replica, then
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writes are disabled only on that replica. In this case, the
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Master might see <a class="ulink" href="../java/com/sleepycat/je/rep/InsufficientAcksException.html" target="_top">InsufficientAcksException</a> thrown in
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response to a write — if your application's
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durability guarantee cannot be met due to the replica being
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unable to perform writes.
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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="utilities.html">Prev</a> </td>
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||
<td width="20%" align="center">
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<a accesskey="u" href="utilities.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="dbbackup.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">Chapter 4. Utilities </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"> Backing up a Replicated Application</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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