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225 lines
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<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
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XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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This file is generated from xml source: DO NOT EDIT
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-->
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<title>mod_lbmethod_byrequests - Apache HTTP Server</title>
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<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
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<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
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<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" />
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<link href="../images/favicon.ico" rel="shortcut icon" /></head>
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<body>
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<div id="page-header">
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
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<p class="apache">Apache HTTP Server Version 2.3</p>
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<img alt="" src="../images/feather.gif" /></div>
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<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
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<div id="path">
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.3</a> > <a href="./">Modules</a></div>
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<div id="page-content">
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<div id="preamble"><h1>Apache Module mod_lbmethod_byrequests</h1>
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<div class="toplang">
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<p><span>Available Languages: </span><a href="../en/mod/mod_lbmethod_byrequests.html" title="English"> en </a></p>
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</div>
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Request Counting load balancer scheduler algorithm for <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code></td></tr>
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<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
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<tr><th><a href="module-dict.html#ModuleIdentifier">Module<EFBFBD>Identifier:</a></th><td>lbmethod_byrequests_module</td></tr>
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<tr><th><a href="module-dict.html#SourceFile">Source<EFBFBD>File:</a></th><td>mod_lbmethod_byrequests.c</td></tr>
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<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>
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<h3>Summary</h3>
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<p>This document is still under development.</p>
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</div>
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<div id="quickview"><h3 class="directives">Directives</h3>
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<p>This module provides no
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directives.</p>
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<h3>Topics</h3>
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<ul id="topics">
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<li><img alt="" src="../images/down.gif" /> <a href="#requests">Request Counting Algorithm</a></li>
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</ul><h3>See also</h3>
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<ul class="seealso">
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<li><code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code></li>
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<li><code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code></li>
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</ul></div>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="requests" id="requests">Request Counting Algorithm</a></h2>
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<p>Enabled via <code>lbmethod=byrequests</code>, the idea behind this
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scheduler is that we distribute the requests among the
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various workers to ensure that each gets their configured share
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of the number of requests. It works as follows:</p>
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<p><dfn>lbfactor</dfn> is <em>how much we expect this worker
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to work</em>, or <em>the workers's work quota</em>. This is
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a normalized value representing their "share" of the amount of
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work to be done.</p>
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<p><dfn>lbstatus</dfn> is <em>how urgent this worker has to work
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to fulfill its quota of work</em>.</p>
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<p>The <dfn>worker</dfn> is a member of the load balancer,
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usually a remote host serving one of the supported protocols.</p>
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<p>We distribute each worker's work quota to the worker, and then look
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which of them needs to work most urgently (biggest lbstatus). This
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worker is then selected for work, and its lbstatus reduced by the
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total work quota we distributed to all workers. Thus the sum of all
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lbstatus does not change(*) and we distribute the requests
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as desired.</p>
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<p>If some workers are disabled, the others will
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still be scheduled correctly.</p>
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<div class="example"><pre><code>for each worker in workers
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worker lbstatus += worker lbfactor
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total factor += worker lbfactor
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if worker lbstatus > candidate lbstatus
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candidate = worker
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candidate lbstatus -= total factor</code></pre></div>
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<p>If a balancer is configured as follows:</p>
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<table><tr><th>worker</th>
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<th class="data">a</th>
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<th class="data">b</th>
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<th class="data">c</th>
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<th class="data">d</th></tr>
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<tr><th>lbfactor</th>
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<td class="data">25</td>
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<td class="data">25</td>
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<td class="data">25</td>
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<td class="data">25</td></tr>
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<tr><th>lbstatus</th>
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<td class="data">0</td>
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<td class="data">0</td>
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<td class="data">0</td>
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<td class="data">0</td></tr>
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</table>
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<p>And <var>b</var> gets disabled, the following schedule is produced:</p>
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<table><tr><th>worker</th>
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<th class="data">a</th>
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<th class="data">b</th>
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<th class="data">c</th>
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<th class="data">d</th></tr>
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<tr><th>lbstatus</th>
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<td class="data"><em>-50</em></td>
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<td class="data">0</td>
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<td class="data">25</td>
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<td class="data">25</td></tr>
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<tr><th>lbstatus</th>
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<td class="data">-25</td>
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<td class="data">0</td>
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<td class="data"><em>-25</em></td>
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<td class="data">50</td></tr>
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<tr><th>lbstatus</th>
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<td class="data">0</td>
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<td class="data">0</td>
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<td class="data">0</td>
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<td class="data"><em>0</em></td></tr>
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<tr><td class="data" colspan="5">(repeat)</td></tr>
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</table>
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<p>That is it schedules: <var>a</var> <var>c</var> <var>d</var>
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<var>a</var> <var>c</var> <var>d</var> <var>a</var> <var>c</var>
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<var>d</var> ... Please note that:</p>
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<table><tr><th>worker</th>
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<th class="data">a</th>
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<th class="data">b</th>
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<th class="data">c</th>
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<th class="data">d</th></tr>
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<tr><th>lbfactor</th>
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<td class="data">25</td>
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<td class="data">25</td>
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<td class="data">25</td>
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<td class="data">25</td></tr>
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</table>
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<p>Has the exact same behavior as:</p>
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<table><tr><th>worker</th>
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<th class="data">a</th>
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<th class="data">b</th>
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<th class="data">c</th>
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<th class="data">d</th></tr>
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<tr><th>lbfactor</th>
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<td class="data">1</td>
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<td class="data">1</td>
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<td class="data">1</td>
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<td class="data">1</td></tr>
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</table>
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<p>This is because all values of <dfn>lbfactor</dfn> are normalized
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with respect to the others. For:</p>
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<table><tr><th>worker</th>
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<th class="data">a</th>
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<th class="data">b</th>
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<th class="data">c</th></tr>
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<tr><th>lbfactor</th>
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<td class="data">1</td>
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<td class="data">4</td>
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<td class="data">1</td></tr>
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</table>
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<p>worker <var>b</var> will, on average, get 4 times the requests
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that <var>a</var> and <var>c</var> will.</p>
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<p>The following asymmetric configuration works as one would expect:</p>
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<table><tr><th>worker</th>
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<th class="data">a</th>
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<th class="data">b</th></tr>
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<tr><th>lbfactor</th>
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<td class="data">70</td>
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<td class="data">30</td></tr>
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<tr><td class="data" colspan="2"> </td></tr>
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<tr><th>lbstatus</th>
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<td class="data"><em>-30</em></td>
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<td class="data">30</td></tr>
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<tr><th>lbstatus</th>
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<td class="data">40</td>
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<td class="data"><em>-40</em></td></tr>
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<tr><th>lbstatus</th>
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<td class="data"><em>10</em></td>
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<td class="data">-10</td></tr>
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<tr><th>lbstatus</th>
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<td class="data"><em>-20</em></td>
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<td class="data">20</td></tr>
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<tr><th>lbstatus</th>
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<td class="data"><em>-50</em></td>
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<td class="data">50</td></tr>
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<tr><th>lbstatus</th>
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<td class="data">20</td>
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<td class="data"><em>-20</em></td></tr>
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<tr><th>lbstatus</th>
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<td class="data"><em>-10</em></td>
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<td class="data">10</td></tr>
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<tr><th>lbstatus</th>
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<td class="data"><em>-40</em></td>
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<td class="data">40</td></tr>
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<tr><th>lbstatus</th>
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<td class="data">30</td>
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<td class="data"><em>-30</em></td></tr>
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<tr><th>lbstatus</th>
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<td class="data"><em>0</em></td>
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<td class="data">0</td></tr>
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<tr><td class="data" colspan="3">(repeat)</td></tr>
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</table>
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<p>That is after 10 schedules, the schedule repeats and 7 <var>a</var>
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are selected with 3 <var>b</var> interspersed.</p>
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</div>
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</div>
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<div class="bottomlang">
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<p><span>Available Languages: </span><a href="../en/mod/mod_lbmethod_byrequests.html" title="English"> en </a></p>
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</div><div id="footer">
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<p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>
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