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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 15:01:30 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 15:01:30 +0000
commit6beeb1b708550be0d4a53b272283e17e5e35fe17 (patch)
tree1ce8673d4aaa948e5554000101f46536a1e4cc29 /docs/manual/mod/mod_lbmethod_byrequests.html.en
parentInitial commit. (diff)
downloadapache2-6beeb1b708550be0d4a53b272283e17e5e35fe17.tar.xz
apache2-6beeb1b708550be0d4a53b272283e17e5e35fe17.zip
Adding upstream version 2.4.57.upstream/2.4.57
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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+<!--
+ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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+<title>mod_lbmethod_byrequests - Apache HTTP Server Version 2.4</title>
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+<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>
+<p class="apache">Apache HTTP Server Version 2.4</p>
+<img alt="" src="../images/feather.png" /></div>
+<div class="up"><a href="./"><img title="&lt;-" alt="&lt;-" src="../images/left.gif" /></a></div>
+<div id="path">
+<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 2.4</a> &gt; <a href="./">Modules</a></div>
+<div id="page-content">
+<div id="preamble"><h1>Apache Module mod_lbmethod_byrequests</h1>
+<div class="toplang">
+<p><span>Available Languages: </span><a href="../en/mod/mod_lbmethod_byrequests.html" title="English">&nbsp;en&nbsp;</a> |
+<a href="../fr/mod/mod_lbmethod_byrequests.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a></p>
+</div>
+<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>
+<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
+<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>lbmethod_byrequests_module</td></tr>
+<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_lbmethod_byrequests.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>byrequests</code> load balancing method.</p>
+</div>
+<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>
+<ul id="topics">
+<li><img alt="" src="../images/down.gif" /> <a href="#requests">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__&amp;list_id=144532&amp;product=Apache%20httpd-2&amp;query_format=specific&amp;order=changeddate%20DESC%2Cpriority%2Cbug_severity&amp;component=mod_lbmethod_byrequests">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&amp;component=mod_lbmethod_byrequests">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>
+<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="requests" id="requests">Request Counting Algorithm</a></h2>
+
+ <p>Enabled via <code>lbmethod=byrequests</code>, the idea behind this
+ scheduler is that we distribute the requests among the
+ various workers to ensure that each gets their configured share
+ of the number of requests. It works as follows:</p>
+
+ <p><dfn>lbfactor</dfn> is <em>how much we expect this worker
+ to work</em>, or <em>the workers' work quota</em>. This is
+ a normalized value representing their "share" of the amount of
+ work to be done.</p>
+
+ <p><dfn>lbstatus</dfn> is <em>how urgent this worker has to work
+ to fulfill its quota of work</em>.</p>
+
+ <p>The <dfn>worker</dfn> is a member of the load balancer,
+ usually a remote host serving one of the supported protocols.</p>
+
+ <p>We distribute each worker's work quota to the worker, and then look
+ which of them needs to work most urgently (biggest lbstatus). This
+ worker is then selected for work, and its lbstatus reduced by the
+ total work quota we distributed to all workers. Thus the sum of all
+ lbstatus does not change(*) and we distribute the requests
+ as desired.</p>
+
+ <p>If some workers are disabled, the others will
+ still be scheduled correctly.</p>
+
+ <div class="example"><pre><code>for each worker in workers
+ worker lbstatus += worker lbfactor
+ total factor += worker lbfactor
+ if worker lbstatus &gt; candidate lbstatus
+ candidate = worker
+
+candidate lbstatus -= total factor</code></pre></div>
+
+ <p>If a balancer is configured as follows:</p>
+
+ <table><tr><th>worker</th>
+ <th class="data">a</th>
+ <th class="data">b</th>
+ <th class="data">c</th>
+ <th class="data">d</th></tr>
+<tr><th>lbfactor</th>
+ <td class="data">25</td>
+ <td class="data">25</td>
+ <td class="data">25</td>
+ <td class="data">25</td></tr>
+<tr><th>lbstatus</th>
+ <td class="data">0</td>
+ <td class="data">0</td>
+ <td class="data">0</td>
+ <td class="data">0</td></tr>
+</table>
+
+ <p>And <var>b</var> gets disabled, the following schedule is produced:</p>
+
+ <table><tr><th>worker</th>
+ <th class="data">a</th>
+ <th class="data">b</th>
+ <th class="data">c</th>
+ <th class="data">d</th></tr>
+<tr><th>lbstatus</th>
+ <td class="data"><em>-50</em></td>
+ <td class="data">0</td>
+ <td class="data">25</td>
+ <td class="data">25</td></tr>
+<tr><th>lbstatus</th>
+ <td class="data">-25</td>
+ <td class="data">0</td>
+ <td class="data"><em>-25</em></td>
+ <td class="data">50</td></tr>
+<tr><th>lbstatus</th>
+ <td class="data">0</td>
+ <td class="data">0</td>
+ <td class="data">0</td>
+ <td class="data"><em>0</em></td></tr>
+<tr><td class="data" colspan="5">(repeat)</td></tr>
+</table>
+
+ <p>That is it schedules: <var>a</var> <var>c</var> <var>d</var>
+ <var>a</var> <var>c</var> <var>d</var> <var>a</var> <var>c</var>
+ <var>d</var> ... Please note that:</p>
+
+ <table><tr><th>worker</th>
+ <th class="data">a</th>
+ <th class="data">b</th>
+ <th class="data">c</th>
+ <th class="data">d</th></tr>
+<tr><th>lbfactor</th>
+ <td class="data">25</td>
+ <td class="data">25</td>
+ <td class="data">25</td>
+ <td class="data">25</td></tr>
+</table>
+
+ <p>Has the exact same behavior as:</p>
+
+ <table><tr><th>worker</th>
+ <th class="data">a</th>
+ <th class="data">b</th>
+ <th class="data">c</th>
+ <th class="data">d</th></tr>
+<tr><th>lbfactor</th>
+ <td class="data">1</td>
+ <td class="data">1</td>
+ <td class="data">1</td>
+ <td class="data">1</td></tr>
+</table>
+
+ <p>This is because all values of <dfn>lbfactor</dfn> are normalized
+ with respect to the others. For:</p>
+
+ <table><tr><th>worker</th>
+ <th class="data">a</th>
+ <th class="data">b</th>
+ <th class="data">c</th></tr>
+<tr><th>lbfactor</th>
+ <td class="data">1</td>
+ <td class="data">4</td>
+ <td class="data">1</td></tr>
+</table>
+
+ <p>worker <var>b</var> will, on average, get 4 times the requests
+ that <var>a</var> and <var>c</var> will.</p>
+
+ <p>The following asymmetric configuration works as one would expect:</p>
+
+ <table><tr><th>worker</th>
+ <th class="data">a</th>
+ <th class="data">b</th></tr>
+<tr><th>lbfactor</th>
+ <td class="data">70</td>
+ <td class="data">30</td></tr>
+<tr><td class="data" colspan="2">&nbsp;</td></tr>
+<tr><th>lbstatus</th>
+ <td class="data"><em>-30</em></td>
+ <td class="data">30</td></tr>
+<tr><th>lbstatus</th>
+ <td class="data">40</td>
+ <td class="data"><em>-40</em></td></tr>
+<tr><th>lbstatus</th>
+ <td class="data"><em>10</em></td>
+ <td class="data">-10</td></tr>
+<tr><th>lbstatus</th>
+ <td class="data"><em>-20</em></td>
+ <td class="data">20</td></tr>
+<tr><th>lbstatus</th>
+ <td class="data"><em>-50</em></td>
+ <td class="data">50</td></tr>
+<tr><th>lbstatus</th>
+ <td class="data">20</td>
+ <td class="data"><em>-20</em></td></tr>
+<tr><th>lbstatus</th>
+ <td class="data"><em>-10</em></td>
+ <td class="data">10</td></tr>
+<tr><th>lbstatus</th>
+ <td class="data"><em>-40</em></td>
+ <td class="data">40</td></tr>
+<tr><th>lbstatus</th>
+ <td class="data">30</td>
+ <td class="data"><em>-30</em></td></tr>
+<tr><th>lbstatus</th>
+ <td class="data"><em>0</em></td>
+ <td class="data">0</td></tr>
+<tr><td class="data" colspan="3">(repeat)</td></tr>
+</table>
+
+ <p>That is after 10 schedules, the schedule repeats and 7 <var>a</var>
+ are selected with 3 <var>b</var> interspersed.</p>
+</div>
+</div>
+<div class="bottomlang">
+<p><span>Available Languages: </span><a href="../en/mod/mod_lbmethod_byrequests.html" title="English">&nbsp;en&nbsp;</a> |
+<a href="../fr/mod/mod_lbmethod_byrequests.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a></p>
+</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&amp;A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Libera.chat, or sent to our <a href="https://httpd.apache.org/lists.html">mailing lists</a>.</div>
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