<?xml version="1.0"?>
<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
-<modulesynopsis>
+<!-- $LastChangedRevision$ -->
+
+<!--
+ 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="prefork.xml.meta">
<name>prefork</name>
<description>Implements a non-threaded, pre-forking web server</description>
<summary>
<p>This Multi-Processing Module (MPM) implements a non-threaded,
- pre-forking web server that handles requests in a manner similar
- to Apache 1.3. It is appropriate for sites that need to avoid
+ pre-forking web server. Each server process may answer incoming
+ requests, and a parent process manages the size of the server pool.
+ It is appropriate for sites that need to avoid
threading for compatibility with non-thread-safe libraries. It
is also the best MPM for isolating each request, so that a problem
with a single request will not affect any other.</p>
<p>This MPM is very self-regulating, so it is rarely necessary to
adjust its configuration directives. Most important is that
- <directive module="mpm_common">MaxClients</directive> be big enough to
- handle as many simultaneous requests as you expect to receive, but
+ <directive module="mpm_common">MaxRequestWorkers</directive> be big enough
+ to handle as many simultaneous requests as you expect to receive, but
small enough to assure that there is enough physical RAM for all
processes.</p>
-
</summary>
-<seealso><a href="../bind.html">Setting which addresses and
- ports Apache uses</a></seealso>
+<seealso><a href="../bind.html">Setting which addresses and ports Apache HTTP Server
+uses</a></seealso>
-<section><title>How it Works</title>
+<section id="how-it-works"><title>How it Works</title>
<p>A single control process is responsible for launching child
processes which listen for connections and serve them when they
- arrive. Apache always tries to maintain several <em>spare</em>
+ arrive. Apache httpd always tries to maintain several <dfn>spare</dfn>
or idle server processes, which stand ready to serve incoming
requests. In this way, clients do not need to wait for a new
child processes to be forked before their requests can be
<p>The <directive module="mpm_common">StartServers</directive>,
<directive module="prefork">MinSpareServers</directive>,
<directive module="prefork">MaxSpareServers</directive>, and
- <directive module="mpm_common">MaxClients</directive> regulate how
+ <directive module="mpm_common">MaxRequestWorkers</directive> regulate how
the parent process creates children to serve requests. In general,
- Apache is very self-regulating, so most sites do not need to
+ Apache httpd is very self-regulating, so most sites do not need to
adjust these directives from their default values. Sites which
need to serve more than 256 simultaneous requests may need to
- increase <directive module="mpm_common">MaxClients</directive>,
+ increase <directive module="mpm_common">MaxRequestWorkers</directive>,
while sites with limited memory may need to decrease <directive
- module="mpm_common">MaxClients</directive> to keep the server from
+ module="mpm_common">MaxRequestWorkers</directive> to keep the server from
thrashing (swapping memory to disk and back). More information
about tuning process creation is provided in the <a
href="../misc/perf-tuning.html">performance hints</a>
documentation.</p>
- <p>While the parent process is usually started as root under Unix
- in order to bind to port 80, the child processes are launched by
- Apache as a less-privileged user. The <directive
- module="mpm_common">User</directive> and <directive
- module="mpm_common">Group</directive> directives are used to set
- the privileges of the Apache child processes. The child processes
+ <p>While the parent process is usually started as <code>root</code>
+ under Unix in order to bind to port 80, the child processes are
+ launched by Apache httpd as a less-privileged user. The <directive
+ module="mod_unixd">User</directive> and <directive
+ module="mod_unixd">Group</directive> directives are used to set
+ the privileges of the Apache httpd child processes. The child processes
must be able to read all the content that will be served, but
should have as few privileges beyond that as possible.</p>
- <p><directive module="mpm_common">MaxRequestsPerChild</directive>
+ <p><directive module="mpm_common">MaxConnectionsPerChild</directive>
controls how frequently the server recycles processes by killing
old ones and launching new ones.</p>
+
+ <p>This MPM uses the <code>mpm-accept</code> mutex to serialize
+ access to incoming connections when subject to the thundering herd
+ problem (generally, when there are multiple listening sockets).
+ The implementation aspects of this mutex can be configured with the
+ <directive module="core">Mutex</directive> directive. The <a
+ href="../misc/perf-tuning.html">performance hints</a>
+ documentation has additional information about this mutex.</p>
</section>
-<directivesynopsis location="mpm_common">
-<name>CoreDumpDirectory</name>
+<directivesynopsis location="mpm_common"><name>CoreDumpDirectory</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>PidFile</name>
+<directivesynopsis location="mpm_common"><name>EnableExceptionHook</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>Listen</name>
+<directivesynopsis location="mpm_common"><name>PidFile</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>ListenBacklog</name>
+<directivesynopsis location="mpm_common"><name>Listen</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>LockFile</name>
+<directivesynopsis location="mpm_common"><name>ListenBacklog</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>MaxClients</name>
-</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>MaxRequestsPerChild</name>
+<directivesynopsis location="mpm_common"><name>MaxRequestWorkers</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>MaxSpareServers</name>
+<directivesynopsis location="mpm_common"><name>MaxMemFree</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>MinSpareServers</name>
+<directivesynopsis location="mpm_common"><name>MaxConnectionsPerChild</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>ScoreBoardFile</name>
+<directivesynopsis location="mpm_common"><name>ScoreBoardFile</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>SendBufferSize</name>
+<directivesynopsis location="mpm_common"><name>ReceiveBufferSize</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>ServerLimit</name>
+<directivesynopsis location="mpm_common"><name>SendBufferSize</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>StartServers</name>
+<directivesynopsis location="mpm_common"><name>ServerLimit</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>User</name>
+<directivesynopsis location="mpm_common"><name>StartServers</name>
</directivesynopsis>
-
-<directivesynopsis location="mpm_common">
-<name>Group</name>
+<directivesynopsis location="mod_unixd"><name>User</name>
</directivesynopsis>
-
-<directivesynopsis>
-<name>AcceptMutex</name>
-<description>Method that Apache uses to serialize multiple children
-accepting requests on network sockets</description>
-<syntax>AcceptMutex default|<em>method</em></syntax>
-<default>AcceptMutex default</default>
-<contextlist><context>server config</context></contextlist>
-
-<usage>
- <p>The <directive>AcceptMutex</directive> directives sets the
- method that Apache uses to serialize multiple children accepting
- requests on network sockets. Prior to Apache 2.0, the method was
- selectable only at compile time. The optimal method to use is
- highly architecture and platform dependent. For further details,
- see the <a href="../misc/perf-tuning.html">performance tuning</a>
- documentation.</p>
-
- <p>If this directive is set to <code>default</code>, then the
- compile-time selected default will be used. Other possible
- methods are listed below. Note that not all methods are
- available on all platforms. If a method is specified which is
- not available, a message will be written to the error log
- listing the available methods.</p>
-
- <dl>
- <dt><code>flock</code></dt>
-
- <dd>uses the <code>flock(2)</code> system call to lock the
- file defined by the <directive module="mpm_common"
- >LockFile</directive> directive.</dd>
-
- <dt><code>fcntl</code></dt>
-
- <dd>uses the <code>fnctl(2)</code> system call to lock the
- file defined by the <directive module="mpm_common"
- >LockFile</directive> directive.</dd>
-
- <dt><code>sysvsem</code></dt>
-
- <dd>uses SySV-style semaphores to implement the mutex.</dd>
-
- <dt><code>pthread</code></dt>
-
- <dd>uses POSIX mutexes as implemented by the POSIX Threads
- (PThreads) specification.</dd>
- </dl>
-</usage>
+<directivesynopsis location="mod_unixd"><name>Group</name>
</directivesynopsis>
<directivesynopsis>
<name>MaxSpareServers</name>
<description>Maximum number of idle child server processes</description>
-<syntax>MaxSpareServers <em>number</em><br /></syntax>
+<syntax>MaxSpareServers <var>number</var></syntax>
<default>MaxSpareServers 10</default>
<contextlist><context>server config</context></contextlist>
<p>The <directive>MaxSpareServers</directive> directive sets the
desired maximum number of <em>idle</em> child server processes. An
idle process is one which is not handling a request. If there are
- more than MaxSpareServers idle, then the parent process will kill
- off the excess processes.</p>
+ more than <directive>MaxSpareServers</directive> idle, then the
+ parent process will kill off the excess processes.</p>
<p>Tuning of this parameter should only be necessary on very
busy sites. Setting this parameter to a large number is almost
- always a bad idea.</p>
+ always a bad idea. If you are trying to set the value equal to or lower than
+ <directive module="prefork">MinSpareServers</directive>, Apache HTTP Server
+ will automatically adjust it to <directive
+ >MinSpareServers</directive><code> + 1</code>.</p>
</usage>
<seealso><directive module="prefork">MinSpareServers</directive></seealso>
<seealso><directive module="mpm_common">StartServers</directive></seealso>
+<seealso><directive module="mpm_common">MaxSpareThreads</directive></seealso>
</directivesynopsis>
<directivesynopsis>
<name>MinSpareServers</name>
<description>Minimum number of idle child server processes</description>
-<syntax>MinSpareServers <em>number</em></syntax>
-<default>MinSpareServers 5</default>
+<syntax>MinSpareServers <var>number</var></syntax>
+<default>MinSpareServers 5</default>
<contextlist><context>server config</context></contextlist>
<usage>
<p>The <directive>MinSpareServers</directive> directive sets the
desired minimum number of <em>idle</em> child server processes. An
idle process is one which is not handling a request. If there are
- fewer than MinSpareServers idle, then the parent process creates
- new children at a maximum rate of 1 per second.</p>
+ fewer than <directive>MinSpareServers</directive> idle, then the parent
+ process creates new children: It will spawn one, wait a second, then spawn
+ two, wait a second, then spawn four, and it will
+ continue exponentially until it is spawning 32 children per second. It will
+ stop whenever it satisfies the <directive>MinSpareServers</directive>
+ setting.</p>
<p>Tuning of this parameter should only be necessary on very
busy sites. Setting this parameter to a large number is almost
always a bad idea.</p>
-
- <p>This directive has no effect on Microsoft Windows.</p>
</usage>
<seealso><directive module="prefork">MaxSpareServers</directive></seealso>
<seealso><directive module="mpm_common">StartServers</directive></seealso>
+<seealso><directive module="mpm_common">MinSpareThreads</directive></seealso>
</directivesynopsis>
</modulesynopsis>
projects / apache / blobdiff