apache/docs/manual/mod/worker.xml

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<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
<modulesynopsis>
<name>worker</name>
<description>Multi-Processing Module implementing a hybrid
    multi-threaded multi-process web server</description>
<status>MPM</status>
<sourcefile>worker.c</sourcefile>
<identifier>mpm_worker_module</identifier>

<summary>
    <p>This Multi-Processing Module (MPM) implements a hybrid
    multi-process multi-threaded server.  By using threads to serve
    requests, it is able to serve a large number of requests with
    less system resources than a process-based server.  Yet it
    retains much of the stability of a process-based server by 
    keeping multiple processes available, each with many threads.</p>

    <p>The most important directives used to control this MPM are
    <directive module="mpm_common">ThreadsPerChild</directive>, which
    controls the number of threads deployed by each child process and
    <directive module="mpm_common">MaxClients</directive>, which
    controls the maximum total number of threads that may be
    launched.</p>

</summary>
<seealso><a href="../bind.html">Setting which addresses and
    ports Apache uses</a></seealso>

<section id="how-it-works"><title>How it Works</title>
    <p>Each process has a fixed
    number of threads. The server adjusts to handle load by
    increasing or decreasing the number of processes.</p>

    <p>A single control process is responsible for launching child
    processes. Each child process creates a fixed number of threads as
    specified in the <directive
    module="mpm_common">ThreadsPerChild</directive> directive. The
    individual threads then listen for connections and serve them when
    they arrive.</p>

    <p>Apache always tries to maintain a pool of <dfn>spare</dfn> or
    idle server threads, which stand ready to serve incoming
    requests. In this way, clients do not need to wait for a new
    threads or processes to be created before their requests can be
    served. The number of processes that will initially launched is
    set by the <directive module="mpm_common">StartServers</directive>
    directive. Then during operation, Apache assesses the total number
    of idle threads in all processes, and forks or kills processes to
    keep this number within the boundaries specified by <directive
    module="mpm_common">MinSpareThreads</directive> and <directive
    module="mpm_common">MaxSpareThreads</directive>. Since this
    process is very self-regulating, it is rarely necessary to modify
    these directives from their default values. The maximum number of
    clients that may be served simultaneously (i.e., the maximum total
    number of threads in all processes) is determined by the
    <directive module="mpm_common">MaxClients</directive> directive,
    while the maximum number of processes that can be launched is set
    by the <directive module="mpm_common">ServerLimit</directive>
    directive.  <directive module="mpm_common">ServerLimit</directive>
    multiplied by <directive
    module="mpm_common">ThreadsPerChild</directive> must be greater
    than or equal to <directive
    module="mpm_common">MaxClients</directive></p>

    <p>A typical configuration of the process-thread controls in
    the <module>worker</module> MPM could look as follows:</p>

    <example>
      StartServers         2<br />
      MaxClients         150<br />
      MinSpareThreads     25<br />
      MaxSpareThreads     75<br />
      ThreadsPerChild     25<br />
      ServerLimit         16
    </example>

    <p>While the parent process is usually started as root under Unix
    in order to bind to port 80, the child processes and threads 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
    must be able to read all the content that will be served, but
    should have as few privileges beyond that as possible. In
    addition, unless <a href="../suexec.html">suexec</a> is used,
    these directives also set the privileges which will be inherited
    by CGI scripts.</p>

    <p><directive module="mpm_common">MaxRequestsPerChild</directive>
    controls how frequently the server recycles processes by killing
    old ones and launching new ones.</p>
</section>
 

<directivesynopsis location="mpm_common"><name>CoreDumpDirectory</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>Group</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>PidFile</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>Listen</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>ListenBacklog</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>LockFile</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>MaxClients</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>MaxMemFree</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>MaxRequestsPerChild</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>MaxSpareThreads</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>MinSpareThreads</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>ScoreBoardFile</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>SendBufferSize</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>ServerLimit</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>StartServers</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>ThreadLimit</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>ThreadsPerChild</name>
</directivesynopsis>
<directivesynopsis location="mpm_common"><name>User</name>
</directivesynopsis>

</modulesynopsis>