granicus.if.org Git - apache/blob - docs/manual/mod/mod_lbmethod_byrequests.html.en

   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" />
  12 <link href="../images/favicon.ico" rel="shortcut icon" /></head>
  13 <body>
  14 <div id="page-header">
  15 <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>
  16 <p class="apache">Apache HTTP Server Version 2.3</p>
  17 <img alt="" src="../images/feather.gif" /></div>
  18 <div class="up"><a href="./"><img title="&lt;-" alt="&lt;-" src="../images/left.gif" /></a></div>
  19 <div id="path">
  20 <a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.3</a> &gt; <a href="./">Modules</a></div>
  21 <div id="page-content">
  22 <div id="preamble"><h1>Apache Module mod_lbmethod_byrequests</h1>
  23 <div class="toplang">
  24 <p><span>Available Languages: </span><a href="../en/mod/mod_lbmethod_byrequests.html" title="English">&nbsp;en&nbsp;</a></p>
  25 </div>
  26 <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>
  27 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
  28 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>lbmethod_byrequests_module</td></tr>
  29 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_lbmethod_byrequests.c</td></tr>
  30 <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>
  31 <h3>Summary</h3>
  32
  33  <p>This document is still under development.</p>
  34 </div>
  35 <div id="quickview"><h3 class="directives">Directives</h3>
  36 <p>This module provides no
  37             directives.</p>
  38 <h3>Topics</h3>
  39 <ul id="topics">
  40 <li><img alt="" src="../images/down.gif" /> <a href="#requests">Request Counting Algorithm</a></li>
  41 </ul><h3>See also</h3>
  42 <ul class="seealso">
  43 <li><code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code></li>
  44 <li><code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code></li>
  45 </ul></div>
  46 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  47 <div class="section">
  48 <h2><a name="requests" id="requests">Request Counting Algorithm</a></h2>
  49
  50     <p>Enabled via <code>lbmethod=byrequests</code>, the idea behind this
  51     scheduler is that we distribute the requests among the
  52     various workers to ensure that each gets their configured share
  53     of the number of requests. It works as follows:</p>
  54
  55     <p><dfn>lbfactor</dfn> is <em>how much we expect this worker
  56     to work</em>, or <em>the workers's work quota</em>. This is
  57     a normalized value representing their "share" of the amount of
  58     work to be done.</p>
  59
  60     <p><dfn>lbstatus</dfn> is <em>how urgent this worker has to work
  61     to fulfill its quota of work</em>.</p>
  62
  63     <p>The <dfn>worker</dfn> is a member of the load balancer,
  64     usually a remote host serving one of the supported protocols.</p>
  65
  66     <p>We distribute each worker's work quota to the worker, and then look
  67     which of them needs to work most urgently (biggest lbstatus).  This
  68     worker is then selected for work, and its lbstatus reduced by the
  69     total work quota we distributed to all workers.  Thus the sum of all
  70     lbstatus does not change(*) and we distribute the requests
  71     as desired.</p>
  72
  73     <p>If some workers are disabled, the others will
  74     still be scheduled correctly.</p>
  75
  76     <div class="example"><pre><code>for each worker in workers
  77     worker lbstatus += worker lbfactor
  78     total factor    += worker lbfactor
  79     if worker lbstatus &gt; candidate lbstatus
  80         candidate = worker
  81
  82 candidate lbstatus -= total factor</code></pre></div>
  83
  84     <p>If a balancer is configured as follows:</p>
  85
  86     <table><tr><th>worker</th>
  87         <th class="data">a</th>
  88         <th class="data">b</th>
  89         <th class="data">c</th>
  90         <th class="data">d</th></tr>
  91 <tr><th>lbfactor</th>
  92         <td class="data">25</td>
  93         <td class="data">25</td>
  94         <td class="data">25</td>
  95         <td class="data">25</td></tr>
  96 <tr><th>lbstatus</th>
  97         <td class="data">0</td>
  98         <td class="data">0</td>
  99         <td class="data">0</td>
 100         <td class="data">0</td></tr>
 101 </table>
 102
 103     <p>And <var>b</var> gets disabled, the following schedule is produced:</p>
 104
 105     <table><tr><th>worker</th>
 106         <th class="data">a</th>
 107         <th class="data">b</th>
 108         <th class="data">c</th>
 109         <th class="data">d</th></tr>
 110 <tr><th>lbstatus</th>
 111         <td class="data"><em>-50</em></td>
 112         <td class="data">0</td>
 113         <td class="data">25</td>
 114         <td class="data">25</td></tr>
 115 <tr><th>lbstatus</th>
 116         <td class="data">-25</td>
 117         <td class="data">0</td>
 118         <td class="data"><em>-25</em></td>
 119         <td class="data">50</td></tr>
 120 <tr><th>lbstatus</th>
 121         <td class="data">0</td>
 122         <td class="data">0</td>
 123         <td class="data">0</td>
 124         <td class="data"><em>0</em></td></tr>
 125 <tr><td class="data" colspan="5">(repeat)</td></tr>
 126 </table>
 127
 128     <p>That is it schedules: <var>a</var> <var>c</var> <var>d</var>
 129     <var>a</var> <var>c</var> <var>d</var> <var>a</var> <var>c</var>
 130     <var>d</var> ... Please note that:</p>
 131
 132     <table><tr><th>worker</th>
 133         <th class="data">a</th>
 134         <th class="data">b</th>
 135         <th class="data">c</th>
 136         <th class="data">d</th></tr>
 137 <tr><th>lbfactor</th>
 138         <td class="data">25</td>
 139         <td class="data">25</td>
 140         <td class="data">25</td>
 141         <td class="data">25</td></tr>
 142 </table>
 143
 144     <p>Has the exact same behavior as:</p>
 145
 146     <table><tr><th>worker</th>
 147         <th class="data">a</th>
 148         <th class="data">b</th>
 149         <th class="data">c</th>
 150         <th class="data">d</th></tr>
 151 <tr><th>lbfactor</th>
 152         <td class="data">1</td>
 153         <td class="data">1</td>
 154         <td class="data">1</td>
 155         <td class="data">1</td></tr>
 156 </table>
 157
 158     <p>This is because all values of <dfn>lbfactor</dfn> are normalized
 159     with respect to the others. For:</p>
 160
 161     <table><tr><th>worker</th>
 162         <th class="data">a</th>
 163         <th class="data">b</th>
 164         <th class="data">c</th></tr>
 165 <tr><th>lbfactor</th>
 166         <td class="data">1</td>
 167         <td class="data">4</td>
 168         <td class="data">1</td></tr>
 169 </table>
 170
 171     <p>worker <var>b</var> will, on average, get 4 times the requests
 172     that <var>a</var> and <var>c</var> will.</p>
 173
 174     <p>The following asymmetric configuration works as one would expect:</p>
 175
 176     <table><tr><th>worker</th>
 177         <th class="data">a</th>
 178         <th class="data">b</th></tr>
 179 <tr><th>lbfactor</th>
 180         <td class="data">70</td>
 181         <td class="data">30</td></tr>
 182 <tr><td class="data" colspan="2">&nbsp;</td></tr>
 183 <tr><th>lbstatus</th>
 184         <td class="data"><em>-30</em></td>
 185         <td class="data">30</td></tr>
 186 <tr><th>lbstatus</th>
 187         <td class="data">40</td>
 188         <td class="data"><em>-40</em></td></tr>
 189 <tr><th>lbstatus</th>
 190         <td class="data"><em>10</em></td>
 191         <td class="data">-10</td></tr>
 192 <tr><th>lbstatus</th>
 193         <td class="data"><em>-20</em></td>
 194         <td class="data">20</td></tr>
 195 <tr><th>lbstatus</th>
 196         <td class="data"><em>-50</em></td>
 197         <td class="data">50</td></tr>
 198 <tr><th>lbstatus</th>
 199         <td class="data">20</td>
 200         <td class="data"><em>-20</em></td></tr>
 201 <tr><th>lbstatus</th>
 202         <td class="data"><em>-10</em></td>
 203         <td class="data">10</td></tr>
 204 <tr><th>lbstatus</th>
 205         <td class="data"><em>-40</em></td>
 206         <td class="data">40</td></tr>
 207 <tr><th>lbstatus</th>
 208         <td class="data">30</td>
 209         <td class="data"><em>-30</em></td></tr>
 210 <tr><th>lbstatus</th>
 211         <td class="data"><em>0</em></td>
 212         <td class="data">0</td></tr>
 213 <tr><td class="data" colspan="3">(repeat)</td></tr>
 214 </table>
 215
 216     <p>That is after 10 schedules, the schedule repeats and 7 <var>a</var>
 217     are selected with 3 <var>b</var> interspersed.</p>
 218 </div>
 219 </div>
 220 <div class="bottomlang">
 221 <p><span>Available Languages: </span><a href="../en/mod/mod_lbmethod_byrequests.html" title="English">&nbsp;en&nbsp;</a></p>
 222 </div><div id="footer">
 223 <p class="apache">Copyright 2010 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>
 224 <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>
 225 </body></html>