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authorhongbotian <hongbo.tianhongbo@huawei.com>2015-11-30 01:45:08 -0500
committerhongbotian <hongbo.tianhongbo@huawei.com>2015-11-30 01:45:08 -0500
commite8ec7aa8e38a93f5b034ac74cebce5de23710317 (patch)
treeaa031937bf856c1f8d6ad7877b8d2cb0224da5ef /rubbos/app/httpd-2.0.64/docs/manual/misc/descriptors.html.en
parentcc40af334e619bb549038238507407866f774f8f (diff)
upload http
JIRA: BOTTLENECK-10 Change-Id: I7598427ff904df438ce77c2819ee48ac75ffa8da Signed-off-by: hongbotian <hongbo.tianhongbo@huawei.com>
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+<?xml version="1.0" encoding="ISO-8859-1"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
+ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+ This file is generated from xml source: DO NOT EDIT
+ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+ -->
+<title>Descriptors and Apache - Apache HTTP Server</title>
+<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
+<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
+<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" />
+<link href="../images/favicon.ico" rel="shortcut icon" /></head>
+<body id="manual-page"><div id="page-header">
+<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>
+<p class="apache">Apache HTTP Server Version 2.0</p>
+<img alt="" src="../images/feather.gif" /></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 2.0</a> &gt; <a href="./">Miscellaneous Documentation</a></div><div id="page-content"><div id="preamble"><h1>Descriptors and Apache</h1>
+<div class="toplang">
+<p><span>Available Languages: </span><a href="../en/misc/descriptors.html" title="English">&nbsp;en&nbsp;</a></p>
+</div>
+
+
+ <div class="warning"><h3>Warning:</h3>
+ <p>This document has not been fully updated
+ to take into account changes made in the 2.0 version of the
+ Apache HTTP Server. Some of the information may still be
+ relevant, but please use it with care.</p>
+ </div>
+
+ <p>A <em>descriptor</em>, also commonly called a <em>file
+ handle</em> is an object that a program uses to read or write
+ an open file, or open network socket, or a variety of other
+ devices. It is represented by an integer, and you may be
+ familiar with <code>stdin</code>, <code>stdout</code>, and
+ <code>stderr</code> which are descriptors 0, 1, and 2
+ respectively. Apache needs a descriptor for each log file, plus
+ one for each network socket that it listens on, plus a handful
+ of others. Libraries that Apache uses may also require
+ descriptors. Normal programs don't open up many descriptors at
+ all, and so there are some latent problems that you may
+ experience should you start running Apache with many
+ descriptors (<em>i.e.</em>, with many virtual hosts).</p>
+
+ <p>The operating system enforces a limit on the number of
+ descriptors that a program can have open at a time. There are
+ typically three limits involved here. One is a kernel
+ limitation, depending on your operating system you will either
+ be able to tune the number of descriptors available to higher
+ numbers (this is frequently called <em>FD_SETSIZE</em>). Or you
+ may be stuck with a (relatively) low amount. The second limit
+ is called the <em>hard resource</em> limit, and it is sometimes
+ set by root in an obscure operating system file, but frequently
+ is the same as the kernel limit. The third limit is called the
+ <em>soft resource</em> limit. The soft limit is always less
+ than or equal to the hard limit. For example, the hard limit
+ may be 1024, but the soft limit only 64. Any user can raise
+ their soft limit up to the hard limit. Root can raise the hard
+ limit up to the system maximum limit. The soft limit is the
+ actual limit that is used when enforcing the maximum number of
+ files a process can have open.</p>
+
+ <p>To summarize:</p>
+
+<div class="example"><p><code>
+ #open files &lt;= soft limit &lt;= hard limit &lt;= kernel limit
+</code></p></div>
+
+
+ <p>You control the hard and soft limits using the
+ <code>limit</code> (csh) or <code>ulimit</code> (sh)
+ directives. See the respective man pages for more information.
+ For example you can probably use <code>ulimit -n
+ unlimited</code> to raise your soft limit up to the hard limit.
+ You should include this command in a shell script which starts
+ your webserver.</p>
+
+ <p>Unfortunately, it's not always this simple. As mentioned
+ above, you will probably run into some system limitations that
+ will need to be worked around somehow. Work was done in version
+ 1.2.1 to improve the situation somewhat. Here is a partial list
+ of systems and workarounds (assuming you are using 1.2.1 or
+ later).</p>
+
+ </div>
+<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#bsdi">BSDI 2.0</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#freebsd">FreeBSD 2.2, BSDI 2.1+</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#linux">Linux</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#solaris">Solaris through 2.5.1</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#AIX">AIX</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#sco">SCO OpenServer</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#tru64">Compaq Tru64 UNIX/Digital UNIX/OSF</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#others">Others</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="bsdi" id="bsdi">BSDI 2.0</a></h2>
+
+ <p>Under BSDI 2.0 you can build Apache to support more
+ descriptors by adding <code>-DFD_SETSIZE=nnn</code> to
+ <code>EXTRA_CFLAGS</code> (where nnn is the number of
+ descriptors you wish to support, keep it less than the hard
+ limit). But it will run into trouble if more than
+ approximately 240 Listen directives are used. This may be
+ cured by rebuilding your kernel with a higher
+ FD_SETSIZE.</p>
+
+ </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="freebsd" id="freebsd">FreeBSD 2.2, BSDI 2.1+</a></h2>
+
+ <p>Similar to the BSDI 2.0 case, you should define
+ <code>FD_SETSIZE</code> and rebuild. But the extra Listen
+ limitation doesn't exist.</p>
+
+ </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="linux" id="linux">Linux</a></h2>
+
+ <p>By default Linux has a kernel maximum of 256 open
+ descriptors per process. There are several patches available
+ for the 2.0.x series which raise this to 1024 and beyond, and
+ you can find them in the "unofficial patches" section of <a href="http://www.linuxhq.com/">the Linux Information HQ</a>.
+ None of these patches are perfect, and an entirely different
+ approach is likely to be taken during the 2.1.x development.
+ Applying these patches will raise the FD_SETSIZE used to
+ compile all programs, and unless you rebuild all your
+ libraries you should avoid running any other program with a
+ soft descriptor limit above 256. As of this writing the
+ patches available for increasing the number of descriptors do
+ not take this into account. On a dedicated webserver you
+ probably won't run into trouble.</p>
+
+ </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="solaris" id="solaris">Solaris through 2.5.1</a></h2>
+
+ <p>Solaris has a kernel hard limit of 1024 (may be lower in
+ earlier versions). But it has a limitation that files using
+ the stdio library cannot have a descriptor above 255. Apache
+ uses the stdio library for the ErrorLog directive. When you
+ have more than approximately 110 virtual hosts (with an error
+ log and an access log each) you will need to build Apache
+ with <code>-DHIGH_SLACK_LINE=256</code> added to
+ <code>EXTRA_CFLAGS</code>. You will be limited to
+ approximately 240 error logs if you do this.</p>
+
+ </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="AIX" id="AIX">AIX</a></h2>
+
+ <p>AIX version 3.2?? appears to have a hard limit of 128
+ descriptors. End of story. Version 4.1.5 has a hard limit of
+ 2000.</p>
+
+ </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="sco" id="sco">SCO OpenServer</a></h2>
+
+ <p>Edit the <code>/etc/conf/cf.d/stune</code> file or use
+ <code>/etc/conf/cf.d/configure</code> choice 7 (User and
+ Group configuration) and modify the <code>NOFILES</code>
+ kernel parameter to a suitably higher value. SCO recommends a
+ number between 60 and 11000, the default is 110. Relink and
+ reboot, and the new number of descriptors will be
+ available.</p>
+
+ </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="tru64" id="tru64">Compaq Tru64 UNIX/Digital UNIX/OSF</a></h2>
+
+ <ol>
+ <li>Raise <code>open_max_soft</code> and
+ <code>open_max_hard</code> to 4096 in the proc subsystem.
+ Do a man on sysconfig, sysconfigdb, and
+ sysconfigtab.</li>
+
+ <li>Raise <code>max-vnodes</code> to a large number which
+ is greater than the number of apache processes * 4096
+ (Setting it to 250,000 should be good for most people).
+ Do a man on sysconfig, sysconfigdb, and
+ sysconfigtab.</li>
+
+ <li>If you are using Tru64 5.0, 5.0A, or 5.1, define
+ <code>NO_SLACK</code> to work around a bug in the OS.
+ <code>CFLAGS="-DNO_SLACK" ./configure</code></li>
+ </ol>
+
+ </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="others" id="others">Others</a></h2>
+
+ <p>If you have details on another operating system, please
+ submit it through our <a href="http://httpd.apache.org/bug_report.html">Bug Report
+ Page</a>.</p>
+
+ <p>In addition to the problems described above there are
+ problems with many libraries that Apache uses. The most common
+ example is the bind DNS resolver library that is used by pretty
+ much every unix, which fails if it ends up with a descriptor
+ above 256. We suspect there are other libraries that similar
+ limitations. So the code as of 1.2.1 takes a defensive stance
+ and tries to save descriptors less than 16 for use while
+ processing each request. This is called the <em>low slack
+ line</em>.</p>
+
+ <p>Note that this shouldn't waste descriptors. If you really
+ are pushing the limits and Apache can't get a descriptor above
+ 16 when it wants it, it will settle for one below 16.</p>
+
+ <p>In extreme situations you may want to lower the low slack
+ line, but you shouldn't ever need to. For example, lowering it
+ can increase the limits 240 described above under Solaris and
+ BSDI 2.0. But you'll play a delicate balancing game with the
+ descriptors needed to serve a request. Should you want to play
+ this game, the compile time parameter is
+ <code>LOW_SLACK_LINE</code> and there's a tiny bit of
+ documentation in the header file <code>httpd.h</code>.</p>
+
+ <p>Finally, if you suspect that all this slack stuff is causing
+ you problems, you can disable it. Add <code>-DNO_SLACK</code>
+ to <code>EXTRA_CFLAGS</code> and rebuild. But please report it
+ to our <a href="http://httpd.apache.org/bug_report.html">Bug
+ Report Page</a> so that we can investigate. </p>
+
+ </div></div>
+<div class="bottomlang">
+<p><span>Available Languages: </span><a href="../en/misc/descriptors.html" title="English">&nbsp;en&nbsp;</a></p>
+</div><div id="footer">
+<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>
+<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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