<div class="wiki-content maincontent"><p>Scaling to tens of thousands of Queues in a single broker is relatively straightforward - but requires some configuration changes from the default.</p><h2 id="ScalingQueues-ReducingThreads">Reducing Threads</h2><p>With the default configuration, ActiveMQ is configured to use a dispatch thread per Queue - you can use set the optimizedDispatch property on the destination policy entry - see <a shape="rect" href="per-destination-policies.xml">configuring Queues</a>.</p><p>ActiveMQ can optionally use internally a thread pool to control dispatching of messages - but as a lot of deployment operating systems are good at handling a large number of threads, this is off by default. To enable this option, either set the ACTIVEMQ_OPTS to disable dedicated task runners in the start up script, INSTALL_DIR/bin/activemq -e.g.</p><div class="code panel pdl" style="border-width: 1px;"><div class="codeContent panelContent pdl">
<script class="brush: java; gutter: false; theme: Default" type="syntaxhighlighter"><![CDATA[ACTIVEMQ_OPTS=&quot;-Xmx512M -Dorg.apache.activemq.UseDedicatedTaskRunner=false&quot;  
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</div></div><p>or you can set ACTIVEMQ_OPTS in /etc/activemq.conf.</p><p><strong>Note:</strong> From ActiveMQ 5.6 onwards the dedicated task runner is disabled by default (see 
    <span class="jira-issue resolved">
        <a shape="rect" class="jira-issue-key" href="https://issues.apache.org/jira/browse/AMQ-3667?src=confmacro"><img class="icon" src="https://issues.apache.org/jira/images/icons/issuetypes/improvement.png">AMQ-3667</a>
                
                                            <span class="aui-lozenge aui-lozenge-subtle aui-lozenge-success jira-macro-single-issue-export-pdf">Resolved</span>
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).</p><p>To reduce the number of threads used for the transport - take a look at using the NIO transport - see <a shape="rect" href="configuring-transports.xml">Configuring Transports</a></p><p>Here is an <a shape="rect" class="external-link" href="http://svn.apache.org/repos/asf/activemq/trunk/assembly/src/sample-conf/activemq-scalability.xml">example</a> of this in use in one of the provided sample broker configuration files.</p><h2 id="ScalingQueues-ReducingMemoryConsumption">Reducing Memory Consumption</h2><p>Reduce the memory used per thread - see <a shape="rect" href="javalangoutofmemory.xml">reducing memory consumption</a></p><h2 id="ScalingQueues-Reducenumberoffiledescriptors">Reduce number of file descriptors</h2><p>ActiveMQ uses the amqPersistenceAdapter by default for persistent messages. Unfortunately, this persistence adapter (as well as the kahaPersistenceAdapter) opens a file descriptor for each queue. When creating large numbers of queues, you'll quickly run into the limit for your OS.</p><p>You can either choose another <a shape="rect" href="persistence.xml">persistence option</a></p><p>or - try out the new <a shape="rect" href="kahadb.xml">KahaDB</a> in version 5.3 and higher</p><h2 id="ScalingQueues-Increasethelimitonfiledescriptorsperprocess">Increase the limit on file descriptors per process</h2><p>Try <a shape="rect" class="external-link" href="http://tinyurl.com/o9qs2f" rel="nofollow">googling for the OS you are using</a></p></div>