mirror of
https://github.com/apache/httpd.git
synced 2025-07-30 20:03:10 +03:00
9cf83a220a
Fix the number of available load balancer scheduler algorithms and add a link to the corresponding module. (lbmethod_heartbeat was missing in the list) git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1829613 13f79535-47bb-0310-9956-ffa450edef68
221 lines
6.6 KiB
XML
221 lines
6.6 KiB
XML
<?xml version="1.0"?>
|
|
<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
|
|
<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
|
|
<!-- $LastChangedRevision$ -->
|
|
|
|
<!--
|
|
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
|
|
|
|
http://www.apache.org/licenses/LICENSE-2.0
|
|
|
|
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_byrequests.xml.meta">
|
|
|
|
<name>mod_lbmethod_byrequests</name>
|
|
<description>Request Counting load balancer scheduler algorithm for <module
|
|
>mod_proxy_balancer</module></description>
|
|
<status>Extension</status>
|
|
<sourcefile>mod_lbmethod_byrequests.c</sourcefile>
|
|
<identifier>lbmethod_byrequests_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>byrequests</code> load balancing method.</p>
|
|
</summary>
|
|
<seealso><module>mod_proxy</module></seealso>
|
|
<seealso><module>mod_proxy_balancer</module></seealso>
|
|
|
|
<section id="requests">
|
|
<title>Request Counting Algorithm</title>
|
|
<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>
|
|
|
|
<example><pre><code>for each worker in workers
|
|
worker lbstatus += worker lbfactor
|
|
total factor += worker lbfactor
|
|
if worker lbstatus > candidate lbstatus
|
|
candidate = worker
|
|
|
|
candidate lbstatus -= total factor</code></pre>
|
|
</example>
|
|
|
|
<p>If a balancer is configured as follows:</p>
|
|
|
|
<table style="data">
|
|
<tr><th>worker</th>
|
|
<th>a</th>
|
|
<th>b</th>
|
|
<th>c</th>
|
|
<th>d</th></tr>
|
|
<tr><th>lbfactor</th>
|
|
<td>25</td>
|
|
<td>25</td>
|
|
<td>25</td>
|
|
<td>25</td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td>0</td>
|
|
<td>0</td>
|
|
<td>0</td>
|
|
<td>0</td></tr>
|
|
</table>
|
|
|
|
<p>And <var>b</var> gets disabled, the following schedule is produced:</p>
|
|
|
|
<table style="data">
|
|
<tr><th>worker</th>
|
|
<th>a</th>
|
|
<th>b</th>
|
|
<th>c</th>
|
|
<th>d</th></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td><em>-50</em></td>
|
|
<td>0</td>
|
|
<td>25</td>
|
|
<td>25</td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td>-25</td>
|
|
<td>0</td>
|
|
<td><em>-25</em></td>
|
|
<td>50</td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td>0</td>
|
|
<td>0</td>
|
|
<td>0</td>
|
|
<td><em>0</em></td></tr>
|
|
<tr><td 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 style="data">
|
|
<tr><th>worker</th>
|
|
<th>a</th>
|
|
<th>b</th>
|
|
<th>c</th>
|
|
<th>d</th></tr>
|
|
<tr><th>lbfactor</th>
|
|
<td>25</td>
|
|
<td>25</td>
|
|
<td>25</td>
|
|
<td>25</td></tr>
|
|
</table>
|
|
|
|
<p>Has the exact same behavior as:</p>
|
|
|
|
<table style="data">
|
|
<tr><th>worker</th>
|
|
<th>a</th>
|
|
<th>b</th>
|
|
<th>c</th>
|
|
<th>d</th></tr>
|
|
<tr><th>lbfactor</th>
|
|
<td>1</td>
|
|
<td>1</td>
|
|
<td>1</td>
|
|
<td>1</td></tr>
|
|
</table>
|
|
|
|
<p>This is because all values of <dfn>lbfactor</dfn> are normalized
|
|
with respect to the others. For:</p>
|
|
|
|
<table style="data">
|
|
<tr><th>worker</th>
|
|
<th>a</th>
|
|
<th>b</th>
|
|
<th>c</th></tr>
|
|
<tr><th>lbfactor</th>
|
|
<td>1</td>
|
|
<td>4</td>
|
|
<td>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 style="data">
|
|
<tr><th>worker</th>
|
|
<th>a</th>
|
|
<th>b</th></tr>
|
|
<tr><th>lbfactor</th>
|
|
<td>70</td>
|
|
<td>30</td></tr>
|
|
<tr><td colspan="2"> </td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td><em>-30</em></td>
|
|
<td>30</td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td>40</td>
|
|
<td><em>-40</em></td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td><em>10</em></td>
|
|
<td>-10</td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td><em>-20</em></td>
|
|
<td>20</td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td><em>-50</em></td>
|
|
<td>50</td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td>20</td>
|
|
<td><em>-20</em></td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td><em>-10</em></td>
|
|
<td>10</td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td><em>-40</em></td>
|
|
<td>40</td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td>30</td>
|
|
<td><em>-30</em></td></tr>
|
|
<tr><th>lbstatus</th>
|
|
<td><em>0</em></td>
|
|
<td>0</td></tr>
|
|
<tr><td 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>
|
|
</section>
|
|
|
|
</modulesynopsis>
|