<?xml version="1.0"?>
<!-- $LastChangedRevision$ -->
<!--
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements. See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to You under the Apache License, Version 2.0
(the "License"); you may not use this file except in compliance with
the License. You may obtain a copy of the License at
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
-->
<modulesynopsis metafile="mod_lbmethod_bybusyness.xml.meta">
<name>mod_lbmethod_bybusyness</name>
<description>Pending Request Counting load balancer scheduler algorithm for <module
>mod_proxy_balancer</module></description>
<status>Extension</status>
<identifier>lbmethod_bybusyness_module</identifier>
<compatibility>Split off from <module>mod_proxy_balancer</module> in 2.3</compatibility>
<summary>
<p>This module does not provide any configuration directives of its own.
It requires the services of <module>mod_proxy_balancer</module>, and
provides the <code>bybusyness</code> load balancing method.</p>
</summary>
<seealso><module>mod_proxy</module></seealso>
<seealso><module>mod_proxy_balancer</module></seealso>
<section id="busyness">
<title>Pending Request Counting Algorithm</title>
<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 <module>mod_lbmethod_byrequests</module>).</p>
</section>
</modulesynopsis>