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<div id="preamble"><h1>Apache Module mod_lbmethod_bybusyness</h1>
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Pending Request Counting load balancer scheduler algorithm for <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code></td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">ModuleIdentifier:</a></th><td>lbmethod_bybusyness_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">SourceFile:</a></th><td>mod_lbmethod_bybusyness.c</td></tr>
<tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Split off from <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> in 2.3</td></tr></table>
<h3>Summary</h3>
<p>This module does not provide any configuration directives of its own.
It requires the services of <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code>, and
provides the <code>bybusyness</code> load balancing method.</p>
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<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><h3>Topics</h3>
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<li><img alt="" src="../images/down.gif" /> <a href="#busyness">Pending Request Counting Algorithm</a></li>
</ul><h3 class="directives">Directives</h3>
<p>This module provides no
directives.</p>
<h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mod_lbmethod_bybusyness">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mod_lbmethod_bybusyness">Report a bug</a></li></ul><h3>See also</h3>
<ul class="seealso">
<li><code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code></li>
<li><code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code></li>
<li><a href="#comments_section">Comments</a></li></ul></div>
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<h2><a name="busyness" id="busyness">Pending Request Counting Algorithm</a></h2>
<p>Enabled via <code>lbmethod=bybusyness</code>, this scheduler keeps
track of how many requests each worker is currently assigned at present. A new
request is automatically assigned to the worker with the lowest
number of active requests. This is useful in the case of workers
that queue incoming requests independently of Apache, to ensure that
queue length stays even and a request is always given to the worker
most likely to service it the fastest and reduce latency.</p>
<p>In the case of multiple least-busy workers, the statistics (and
weightings) used by the Request Counting method are used to break the
tie. Over time, the distribution of work will come to resemble that
characteristic of <code>byrequests</code> (as implemented
by <code class="module"><a href="../mod/mod_lbmethod_byrequests.html">mod_lbmethod_byrequests</a></code>).</p>
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