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| <p class="apache">Apache HTTP Server Version 2.4</p> |
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| <div id="preamble"><h1>Apache MPM worker</h1> |
| <div class="toplang"> |
| <p><span>Available Languages: </span><a href="../de/mod/worker.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> | |
| <a href="../en/mod/worker.html" title="English"> en </a> | |
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| <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 |
| fewer system resources than a process-based server. However, 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#maxrequestworkers">MaxRequestWorkers</a></code>, which |
| controls the maximum total number of threads that may be |
| launched.</p> |
| </div> |
| <div id="quickview"><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 class="directives">Directives</h3> |
| <ul id="toc"> |
| <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#enableexceptionhook">EnableExceptionHook</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.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#maxconnectionsperchild">MaxConnectionsPerChild</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#maxrequestworkers">MaxRequestWorkers</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#receivebuffersize">ReceiveBufferSize</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#threadstacksize">ThreadStackSize</a></li> |
| <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li> |
| </ul> |
| <h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mpm_worker">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mpm_worker">Report a bug</a></li></ul><h3>See also</h3> |
| <ul class="seealso"> |
| <li><a href="../bind.html">Setting which addresses and ports Apache HTTP Server uses</a></li> |
| <li><a href="#comments_section">Comments</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>A single control process (the parent) is responsible for launching |
| child processes. Each child process creates a fixed number of server |
| threads as specified in the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive, as well |
| as a listener thread which listens for connections and passes them |
| to a server thread for processing when they arrive.</p> |
| |
| <p>Apache HTTP Server 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 launch is |
| set by the <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code> |
| directive. During operation, the server 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#maxrequestworkers">MaxRequestWorkers</a></code> directive. |
| The maximum number of active child processes is determined by |
| the <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> |
| directive divided by the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild"> |
| ThreadsPerChild</a></code> directive.</p> |
| |
| <p>Two directives set hard limits on the number of active child |
| processes and the number of server threads in a child process, |
| and can only be changed by fully stopping the server and then |
| starting it again. <code class="directive"><a href="../mod/mpm_common.html#serverlimit">ServerLimit |
| </a></code> is a hard limit on the number of active child |
| processes, and must be greater than or equal to the |
| <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> |
| directive divided by the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild"> |
| ThreadsPerChild</a></code> directive. |
| <code class="directive"><a href="../mod/mpm_common.html#threadlimit">ThreadLimit</a></code> is a hard |
| limit of the number of server threads, and must be greater than |
| or equal to the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive.</p> |
| |
| <p>In addition to the set of active child processes, there may |
| be additional child processes which are terminating, but where at |
| least one server thread is still handling an existing client |
| connection. Up to <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> terminating processes |
| may be present, though the actual number can be expected to be |
| much smaller. This behavior can be avoided by disabling the |
| termination of individual child processes, which is achieved using |
| the following:</p> |
| |
| <ul> |
| <li>set the value of <code class="directive"><a href="../mod/mpm_common.html#maxconnectionsperchild"> |
| MaxConnectionsPerChild</a></code> to zero</li> |
| |
| <li>set the value of <code class="directive"><a href="../mod/mpm_common.html#maxsparethreads"> |
| MaxSpareThreads</a></code> to the same value as |
| <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code></li> |
| </ul> |
| |
| <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> |
| |
| <pre class="prettyprint lang-config">ServerLimit 16 |
| StartServers 2 |
| MaxRequestWorkers 150 |
| MinSpareThreads 25 |
| MaxSpareThreads 75 |
| ThreadsPerChild 25</pre> |
| |
| |
| <p>While the parent process is usually started as <code>root</code> |
| under Unix in order to bind to port 80, the child processes and threads |
| are launched by the server as a less-privileged user. The <code class="directive"><a href="../mod/mod_unixd.html#user">User</a></code> and <code class="directive"><a href="../mod/mod_unixd.html#group">Group</a></code> directives are used to set |
| the privileges of the Apache HTTP Server 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 <code class="program"><a href="../programs/suexec.html">suexec</a></code> 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#maxconnectionsperchild">MaxConnectionsPerChild</a></code> |
| 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 |
| <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive. The <a href="../misc/perf-tuning.html">performance hints</a> |
| documentation has additional information about this mutex.</p> |
| </div> |
| </div> |
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