1<?xml version="1.0" encoding="ISO-8859-1"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- 4 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 5 This file is generated from xml source: DO NOT EDIT 6 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 7 --> 8<title>mod_lbmethod_byrequests - Apache HTTP Server</title> 9<link href="/style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> 10<link href="/style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> 11<link href="/style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="/style/css/prettify.css" /> 12<script src="/style/scripts/prettify.min.js" type="text/javascript"> 13</script> 14 15<link href="/images/favicon.ico" rel="shortcut icon" /></head> 16<body> 17<div id="page-header"> 18<p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p> 19<p class="apache">Apache HTTP Server Version 2.4</p> 20<img alt="" src="/images/feather.gif" /></div> 21<div class="up"><a href="./"><img title="<-" alt="<-" src="/images/left.gif" /></a></div> 22<div id="path"> 23<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 2.4</a> > <a href="./">Modules</a></div> 24<div id="page-content"> 25<div id="preamble"><h1>Apache Module mod_lbmethod_byrequests</h1> 26<div class="toplang"> 27<p><span>Available Languages: </span><a href="/en/mod/mod_lbmethod_byrequests.html" title="English"> en </a> | 28<a href="/fr/mod/mod_lbmethod_byrequests.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a></p> 29</div> 30<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> 31<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr> 32<tr><th><a href="module-dict.html#ModuleIdentifier">Module�Identifier:</a></th><td>lbmethod_byrequests_module</td></tr> 33<tr><th><a href="module-dict.html#SourceFile">Source�File:</a></th><td>mod_lbmethod_byrequests.c</td></tr> 34<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> 35<h3>Summary</h3> 36 37<p>This module does not provide any configuration directives of its own. 38It requires the services of <code class="module"><a href="/mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code>, and 39provides the <code>byrequests</code> load balancing method..</p> 40</div> 41<div id="quickview"><h3 class="directives">Directives</h3> 42<p>This module provides no 43 directives.</p> 44<h3>Topics</h3> 45<ul id="topics"> 46<li><img alt="" src="/images/down.gif" /> <a href="#requests">Request Counting Algorithm</a></li> 47</ul><h3>See also</h3> 48<ul class="seealso"> 49<li><code class="module"><a href="/mod/mod_proxy.html">mod_proxy</a></code></li> 50<li><code class="module"><a href="/mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code></li> 51</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div> 52<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 53<div class="section"> 54<h2><a name="requests" id="requests">Request Counting Algorithm</a></h2> 55 56 <p>Enabled via <code>lbmethod=byrequests</code>, the idea behind this 57 scheduler is that we distribute the requests among the 58 various workers to ensure that each gets their configured share 59 of the number of requests. It works as follows:</p> 60 61 <p><dfn>lbfactor</dfn> is <em>how much we expect this worker 62 to work</em>, or <em>the workers' work quota</em>. This is 63 a normalized value representing their "share" of the amount of 64 work to be done.</p> 65 66 <p><dfn>lbstatus</dfn> is <em>how urgent this worker has to work 67 to fulfill its quota of work</em>.</p> 68 69 <p>The <dfn>worker</dfn> is a member of the load balancer, 70 usually a remote host serving one of the supported protocols.</p> 71 72 <p>We distribute each worker's work quota to the worker, and then look 73 which of them needs to work most urgently (biggest lbstatus). This 74 worker is then selected for work, and its lbstatus reduced by the 75 total work quota we distributed to all workers. Thus the sum of all 76 lbstatus does not change(*) and we distribute the requests 77 as desired.</p> 78 79 <p>If some workers are disabled, the others will 80 still be scheduled correctly.</p> 81 82 <div class="example"><pre><code>for each worker in workers 83 worker lbstatus += worker lbfactor 84 total factor += worker lbfactor 85 if worker lbstatus > candidate lbstatus 86 candidate = worker 87 88candidate lbstatus -= total factor</code></pre></div> 89 90 <p>If a balancer is configured as follows:</p> 91 92 <table><tr><th>worker</th> 93 <th class="data">a</th> 94 <th class="data">b</th> 95 <th class="data">c</th> 96 <th class="data">d</th></tr> 97<tr><th>lbfactor</th> 98 <td class="data">25</td> 99 <td class="data">25</td> 100 <td class="data">25</td> 101 <td class="data">25</td></tr> 102<tr><th>lbstatus</th> 103 <td class="data">0</td> 104 <td class="data">0</td> 105 <td class="data">0</td> 106 <td class="data">0</td></tr> 107</table> 108 109 <p>And <var>b</var> gets disabled, the following schedule is produced:</p> 110 111 <table><tr><th>worker</th> 112 <th class="data">a</th> 113 <th class="data">b</th> 114 <th class="data">c</th> 115 <th class="data">d</th></tr> 116<tr><th>lbstatus</th> 117 <td class="data"><em>-50</em></td> 118 <td class="data">0</td> 119 <td class="data">25</td> 120 <td class="data">25</td></tr> 121<tr><th>lbstatus</th> 122 <td class="data">-25</td> 123 <td class="data">0</td> 124 <td class="data"><em>-25</em></td> 125 <td class="data">50</td></tr> 126<tr><th>lbstatus</th> 127 <td class="data">0</td> 128 <td class="data">0</td> 129 <td class="data">0</td> 130 <td class="data"><em>0</em></td></tr> 131<tr><td class="data" colspan="5">(repeat)</td></tr> 132</table> 133 134 <p>That is it schedules: <var>a</var> <var>c</var> <var>d</var> 135 <var>a</var> <var>c</var> <var>d</var> <var>a</var> <var>c</var> 136 <var>d</var> ... Please note that:</p> 137 138 <table><tr><th>worker</th> 139 <th class="data">a</th> 140 <th class="data">b</th> 141 <th class="data">c</th> 142 <th class="data">d</th></tr> 143<tr><th>lbfactor</th> 144 <td class="data">25</td> 145 <td class="data">25</td> 146 <td class="data">25</td> 147 <td class="data">25</td></tr> 148</table> 149 150 <p>Has the exact same behavior as:</p> 151 152 <table><tr><th>worker</th> 153 <th class="data">a</th> 154 <th class="data">b</th> 155 <th class="data">c</th> 156 <th class="data">d</th></tr> 157<tr><th>lbfactor</th> 158 <td class="data">1</td> 159 <td class="data">1</td> 160 <td class="data">1</td> 161 <td class="data">1</td></tr> 162</table> 163 164 <p>This is because all values of <dfn>lbfactor</dfn> are normalized 165 with respect to the others. For:</p> 166 167 <table><tr><th>worker</th> 168 <th class="data">a</th> 169 <th class="data">b</th> 170 <th class="data">c</th></tr> 171<tr><th>lbfactor</th> 172 <td class="data">1</td> 173 <td class="data">4</td> 174 <td class="data">1</td></tr> 175</table> 176 177 <p>worker <var>b</var> will, on average, get 4 times the requests 178 that <var>a</var> and <var>c</var> will.</p> 179 180 <p>The following asymmetric configuration works as one would expect:</p> 181 182 <table><tr><th>worker</th> 183 <th class="data">a</th> 184 <th class="data">b</th></tr> 185<tr><th>lbfactor</th> 186 <td class="data">70</td> 187 <td class="data">30</td></tr> 188<tr><td class="data" colspan="2"> </td></tr> 189<tr><th>lbstatus</th> 190 <td class="data"><em>-30</em></td> 191 <td class="data">30</td></tr> 192<tr><th>lbstatus</th> 193 <td class="data">40</td> 194 <td class="data"><em>-40</em></td></tr> 195<tr><th>lbstatus</th> 196 <td class="data"><em>10</em></td> 197 <td class="data">-10</td></tr> 198<tr><th>lbstatus</th> 199 <td class="data"><em>-20</em></td> 200 <td class="data">20</td></tr> 201<tr><th>lbstatus</th> 202 <td class="data"><em>-50</em></td> 203 <td class="data">50</td></tr> 204<tr><th>lbstatus</th> 205 <td class="data">20</td> 206 <td class="data"><em>-20</em></td></tr> 207<tr><th>lbstatus</th> 208 <td class="data"><em>-10</em></td> 209 <td class="data">10</td></tr> 210<tr><th>lbstatus</th> 211 <td class="data"><em>-40</em></td> 212 <td class="data">40</td></tr> 213<tr><th>lbstatus</th> 214 <td class="data">30</td> 215 <td class="data"><em>-30</em></td></tr> 216<tr><th>lbstatus</th> 217 <td class="data"><em>0</em></td> 218 <td class="data">0</td></tr> 219<tr><td class="data" colspan="3">(repeat)</td></tr> 220</table> 221 222 <p>That is after 10 schedules, the schedule repeats and 7 <var>a</var> 223 are selected with 3 <var>b</var> interspersed.</p> 224</div> 225</div> 226<div class="bottomlang"> 227<p><span>Available Languages: </span><a href="/en/mod/mod_lbmethod_byrequests.html" title="English"> en </a> | 228<a href="/fr/mod/mod_lbmethod_byrequests.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a></p> 229</div><div class="top"><a href="#page-header"><img src="/images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. 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