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| <title>worker - Apache HTTP Server</title> |
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| <p class="apache">Apache HTTP Server Version 2.0</p> |
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| <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">Modules</a></div> |
| <div id="page-content"> |
| <div id="preamble"><h1>Apache MPM worker</h1> |
| <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Multi-Processing Module implementing a hybrid |
| multi-threaded multi-process web server</td></tr> |
| <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr> |
| <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_worker_module</td></tr> |
| <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>worker.c</td></tr></table> |
| <h3>Summary</h3> |
| |
| <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 |
| <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code>, which |
| controls the number of threads deployed by each child process and |
| <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>, which |
| controls the maximum total number of threads that may be |
| launched.</p> |
| </div> |
| <div id="quickview"><h3 class="directives">Directives</h3> |
| <ul id="toc"> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#acceptmutex">AcceptMutex</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#group">Group</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#lockfile">LockFile</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li> |
| </ul> |
| <h3>Topics</h3> |
| <ul id="topics"> |
| <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li> |
| </ul><h3>See also</h3> |
| <ul class="seealso"> |
| <li><a href="../bind.html">Setting which addresses and ports Apache |
| uses</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="how-it-works" id="how-it-works">How it Works</a></h2> |
| <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 <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> 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 <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code> |
| 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 <code class="directive"><a href="../mod/mpm_common.html#minsparethreads">MinSpareThreads</a></code> and <code class="directive"><a href="../mod/mpm_common.html#maxsparethreads">MaxSpareThreads</a></code>. 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 |
| <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> directive, |
| while the maximum number of processes that can be launched is set |
| by the <code class="directive"><a href="../mod/mpm_common.html#serverlimit">ServerLimit</a></code> |
| directive. <code class="directive"><a href="../mod/mpm_common.html#serverlimit">ServerLimit</a></code> |
| multiplied by <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> must be greater |
| than or equal to <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code></p> |
| |
| <p>A typical configuration of the process-thread controls in |
| the <code class="module"><a href="../mod/worker.html">worker</a></code> MPM could look as follows:</p> |
| |
| <div class="example"><p><code> |
| StartServers 2<br /> |
| MaxClients 150<br /> |
| MinSpareThreads 25<br /> |
| MaxSpareThreads 75<br /> |
| ThreadsPerChild 25<br /> |
| ServerLimit 16 |
| </code></p></div> |
| |
| <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 <code class="directive"><a href="../mod/mpm_common.html#user">User</a></code> and <code class="directive"><a href="../mod/mpm_common.html#group">Group</a></code> 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><code class="directive"><a href="../mod/mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></code> |
| controls how frequently the server recycles processes by killing |
| old ones and launching new ones.</p> |
| </div> |
| </div> |
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| <p class="apache">Maintained by the <a href="http://httpd.apache.org/docs-project/">Apache HTTP Server Documentation Project</a></p> |
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