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<title>mod_mem_cache - Apache HTTP Server Version 2.2</title>
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
<p class="apache">Apache HTTP Server Version 2.2</p>
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<div class="retired"><h4>Please note</h4>
<p> This document refers to a legacy release (<strong>2.2</strong>) of Apache httpd. The active release (<strong>2.4</strong>) is documented <a href="http://httpd.apache.org/docs/current">here</a>. If you have not already upgraded, please follow <a href="http://httpd.apache.org/docs/current/upgrading.html">this link</a> for more information.</p>
<p>You may follow <a href="http://httpd.apache.org/docs/current/mod/mod_mem_cache.html">this link</a> to go to the current version of this document.</p></div><div id="preamble"><h1>Apache Module mod_mem_cache</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/mod/mod_mem_cache.html" title="English"> en </a> |
<a href="../ja/mod/mod_mem_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
<a href="../ko/mod/mod_mem_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
</div>
<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Content cache keyed to URIs</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mem_cache_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_mem_cache.c</td></tr></table>
<h3>Summary</h3>
<p>This module <em>requires</em> the service of <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>. It acts as a support module for <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> and provides a memory based storage manager.
<code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code> can be configured to operate in two
modes: caching open file descriptors or caching objects in heap storage.
<code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code> is most useful when used to cache locally
generated content or to cache backend server content for <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> configured for <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code> (aka <dfn>reverse proxy</dfn>).</p>
<p>Content is stored in and retrieved from the cache using URI based
keys. Content with access protection is not cached.</p>
<div class="note"><h3>Note</h3>In most cases <code class="module"><a href="../mod/mod_disk_cache.html">mod_disk_cache</a></code>
should be the preferred choice. This is explained further in the <a href="../caching.html#inmemory">Caching Guide</a>. In particular,
this module's cache is <em>per-process</em>, which can be partially
mitigated by configuring threaded MPMs to use fewer child processes
via configuration of larger values for <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code>. This module's cache is
also limited to storing a single variant (see HTTP Vary: header) of each
resource in the cache.</div>
</div>
<div id="quickview"><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#mcachemaxobjectcount">MCacheMaxObjectCount</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#mcachemaxobjectsize">MCacheMaxObjectSize</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#mcachemaxstreamingbuffer">MCacheMaxStreamingBuffer</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#mcacheminobjectsize">MCacheMinObjectSize</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#mcacheremovalalgorithm">MCacheRemovalAlgorithm</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#mcachesize">MCacheSize</a></li>
</ul>
<h3>See also</h3>
<ul class="seealso">
<li><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code></li>
<li><code class="module"><a href="../mod/mod_disk_cache.html">mod_disk_cache</a></code></li>
</ul><ul class="seealso"><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="directive-section"><h2><a name="MCacheMaxObjectCount" id="MCacheMaxObjectCount">MCacheMaxObjectCount</a> <a name="mcachemaxobjectcount" id="mcachemaxobjectcount">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum number of objects allowed to be placed in the
cache</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MCacheMaxObjectCount <var>value</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MCacheMaxObjectCount 1009</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_mem_cache</td></tr>
</table>
<p>The <code class="directive">MCacheMaxObjectCount</code> directive sets the
maximum number of objects to be cached. The value is used to create the
open hash table. If a new object needs to be inserted in the cache and
the maximum number of objects has been reached, an object will be
removed to allow the new object to be cached. The object to be removed
is selected using the algorithm specified by <code class="directive"><a href="#mcacheremovalalgorithm">MCacheRemovalAlgorithm</a></code>.</p>
<div class="example"><h3>Example</h3><p><code>
MCacheMaxObjectCount 13001
</code></p></div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="MCacheMaxObjectSize" id="MCacheMaxObjectSize">MCacheMaxObjectSize</a> <a name="mcachemaxobjectsize" id="mcachemaxobjectsize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum size (in bytes) of a document allowed in the
cache</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MCacheMaxObjectSize <var>bytes</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MCacheMaxObjectSize 10000</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_mem_cache</td></tr>
</table>
<p>The <code class="directive">MCacheMaxObjectSize</code> directive sets the
maximum allowable size, in bytes, of a document for it to be considered
cacheable.</p>
<div class="example"><h3>Example</h3><p><code>
MCacheMaxObjectSize 6400000
</code></p></div>
<div class="note"><h3>Note</h3>
<p>The value of <code class="directive">MCacheMaxObjectSize</code> must be
greater than the value specified by the <code class="directive"><a href="#mcacheminobjectsize">MCacheMinObjectSize</a></code> directive.</p>
</div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="MCacheMaxStreamingBuffer" id="MCacheMaxStreamingBuffer">MCacheMaxStreamingBuffer</a> <a name="mcachemaxstreamingbuffer" id="mcachemaxstreamingbuffer">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum amount of a streamed response to buffer in memory
before declaring the response uncacheable</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MCacheMaxStreamingBuffer <var>size_in_bytes</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MCacheMaxStreamingBuffer the smaller of 100000 or MCacheMaxObjectSize</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_mem_cache</td></tr>
</table>
<p>The <code class="directive">MCacheMaxStreamingBuffer</code> directive
specifies the maximum number of bytes of a streamed response to
buffer before deciding that the response is too big to cache.
A streamed response is one in which the entire content is not
immediately available and in which the <code>Content-Length</code>
may not be known. Sources of streaming responses include proxied
responses and the output of CGI scripts. By default, a streamed
response will <em>not</em> be cached unless it has a
<code>Content-Length</code> header. The reason for this is to
avoid using a large amount of memory to buffer a partial response
that might end up being too large to fit in the cache.
The <code class="directive">MCacheMaxStreamingBuffer</code> directive allows
buffering of streamed responses that don't contain a
<code>Content-Length</code> up to the specified maximum amount of
space. If the maximum buffer space is reached, the buffered
content is discarded and the attempt to cache is abandoned.</p>
<div class="note"><h3>Note:</h3>
<p>Using a nonzero value for <code class="directive">MCacheMaxStreamingBuffer</code>
will not delay the transmission of the response to the client.
As soon as <code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code> copies a block of streamed
content into a buffer, it sends the block on to the next output
filter for delivery to the client.</p>
</div>
<div class="example"><p><code>
# Enable caching of streamed responses up to 64KB:<br />
MCacheMaxStreamingBuffer 65536
</code></p></div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="MCacheMinObjectSize" id="MCacheMinObjectSize">MCacheMinObjectSize</a> <a name="mcacheminobjectsize" id="mcacheminobjectsize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The minimum size (in bytes) of a document to be allowed in the
cache</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MCacheMinObjectSize <var>bytes</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MCacheMinObjectSize 1</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_mem_cache</td></tr>
</table>
<p>The <code class="directive">MCacheMinObjectSize</code> directive sets the
minimum size in bytes of a document for it to be considered
cacheable.</p>
<div class="example"><h3>Example</h3><p><code>
MCacheMinObjectSize 10000
</code></p></div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="MCacheRemovalAlgorithm" id="MCacheRemovalAlgorithm">MCacheRemovalAlgorithm</a> <a name="mcacheremovalalgorithm" id="mcacheremovalalgorithm">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The algorithm used to select documents for removal from the
cache</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MCacheRemovalAlgorithm LRU|GDSF</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MCacheRemovalAlgorithm GDSF</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_mem_cache</td></tr>
</table>
<p>The <code class="directive">MCacheRemovalAlgorithm</code> directive specifies
the algorithm used to select documents for removal from the cache.
Two choices are available:</p>
<dl>
<dt><code>LRU</code> (Least Recently Used)</dt>
<dd><code>LRU</code> removes the documents that have not been accessed
for the longest time.</dd>
<dt><code>GDSF</code> (GreadyDual-Size)</dt>
<dd><code>GDSF</code> assigns a priority to cached documents based
on the cost of a cache miss and the size of the document. Documents
with the lowest priority are removed first.</dd>
</dl>
<div class="example"><h3>Example</h3><p><code>
MCacheRemovalAlgorithm GDSF<br />
MCacheRemovalAlgorithm LRU
</code></p></div>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="MCacheSize" id="MCacheSize">MCacheSize</a> <a name="mcachesize" id="mcachesize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum amount of memory used by the cache in
KBytes</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MCacheSize <var>KBytes</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MCacheSize 100</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_mem_cache</td></tr>
</table>
<p>The <code class="directive">MCacheSize</code> directive sets the maximum
amount of memory to be used by the cache, in KBytes (1024-byte units).
If a new object needs to be inserted in the cache and the size of the
object is greater than the remaining memory, objects will be removed
until the new object can be cached. The object to be removed is
selected using the algorithm specified by <code class="directive"><a href="#mcacheremovalalgorithm">MCacheRemovalAlgorithm</a></code>.</p>
<div class="example"><h3>Example</h3><p><code>
MCacheSize 700000
</code></p></div>
<div class="note"><h3>Note</h3>
<p>The <code class="directive">MCacheSize</code> value must be greater than
the value specified by the <code class="directive"><a href="#mcachemaxobjectsize">MCacheMaxObjectSize</a></code> directive.</p>
</div>
</div>
</div>
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