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<?xml version="1.0" encoding="utf-8"?>
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<section id="Java-Broker-Runtime-Background-Recovery">
<title>Background Recovery</title>
<para>On startup of the Broker, or restart of a Virtualhost, the Broker restores all durable
queues and their messages from disk. In the Broker's default mode the Virtualhosts do not become
active until this recovery process completes. If queues have a large number of entries, this may
take considerable time. During this time no messaging can be performed.</para>
<para>The Broker has a background recovery feature allows the system to return to operation
sooner. If enabled the recovery process takes place in the background allow producers and
consumers to begin work earlier.</para>
<para>The feature respects the message delivery order requirements of standard queues, that is any
messages arriving whilst the background recovery is in flight won't overtake older messages
still to be recovered from disk. There is an exception for the out of order queue types whilst
background recovery is in flight. For instance, with priority queues older lower priority
messages may be delivered before newer, higher priority.</para>
<para>To activate the feature, set a <link
linkend="Java-Broker-Management-Managing-Entities-General">context variable</link>
<literal>use_async_message_store_recovery</literal> at the desired Virtualhost, or at Broker or
higher to enable the feature broker-wide.</para>
<note>
<para>The background recovery feature does not write operational log messages to indicate its
progress. This means messages <link
linkend="Java-Broker-Appendix-Operation-Logging-Message-MST-1004">MST-1004</link> and <link
linkend="Java-Broker-Appendix-Operation-Logging-Message-MST-1005">MST-1005</link> will not
be seen.</para>
</note>
</section>
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