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8 <title>mod_mem_cache - Apache HTTP Server</title>
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16 <p class="apache">Apache HTTP Server Version 2.0</p>
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20 <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">Modules</a></div>
21 <div id="page-content">
22 <div id="preamble"><h1>Apache Module mod_mem_cache</h1>
24 <p><span>Available Languages: </span><a href="../en/mod/mod_mem_cache.html" title="English"> en </a> |
25 <a href="../ja/mod/mod_mem_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
26 <a href="../ko/mod/mod_mem_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
28 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Content cache keyed to URIs</td></tr>
29 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
30 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mem_cache_module</td></tr>
31 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_mem_cache.c</td></tr></table>
35 This module is experimental. Documentation is still under
39 <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.
40 <code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code> can be configured to operate in two
41 modes: caching open file descriptors or caching objects in heap storage.
42 <code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code> is most useful when used to cache locally
43 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>
45 <p>Content is stored in and retrieved from the cache using URI based
46 keys. Content with access protection is not cached.</p>
48 <div id="quickview"><h3 class="directives">Directives</h3>
50 <li><img alt="" src="../images/down.gif" /> <a href="#mcachemaxobjectcount">MCacheMaxObjectCount</a></li>
51 <li><img alt="" src="../images/down.gif" /> <a href="#mcachemaxobjectsize">MCacheMaxObjectSize</a></li>
52 <li><img alt="" src="../images/down.gif" /> <a href="#mcachemaxstreamingbuffer">MCacheMaxStreamingBuffer</a></li>
53 <li><img alt="" src="../images/down.gif" /> <a href="#mcacheminobjectsize">MCacheMinObjectSize</a></li>
54 <li><img alt="" src="../images/down.gif" /> <a href="#mcacheremovalalgorithm">MCacheRemovalAlgorithm</a></li>
55 <li><img alt="" src="../images/down.gif" /> <a href="#mcachesize">MCacheSize</a></li>
59 <li><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code></li>
60 <li><code class="module"><a href="../mod/mod_disk_cache.html">mod_disk_cache</a></code></li>
63 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
64 <div class="directive-section"><h2><a name="MCacheMaxObjectCount" id="MCacheMaxObjectCount">MCacheMaxObjectCount</a> <a name="mcachemaxobjectcount" id="mcachemaxobjectcount">Directive</a></h2>
65 <table class="directive">
66 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum number of objects allowed to be placed in the
68 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MCacheMaxObjectCount <var>value</var></code></td></tr>
69 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MCacheMaxObjectCount 1009</code></td></tr>
70 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
71 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
72 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_mem_cache</td></tr>
74 <p>The <code class="directive">MCacheMaxObjectCount</code> directive sets the
75 maximum number of objects to be cached. The value is used to create the
76 open hash table. If a new object needs to be inserted in the cache and
77 the maximum number of objects has been reached, an object will be
78 removed to allow the new object to be cached. The object to be removed
79 is selected using the algorithm specified by <code class="directive"><a href="#mcacheremovalalgorithm">MCacheRemovalAlgorithm</a></code>.</p>
81 <div class="example"><h3>Example</h3><p><code>
82 MCacheMaxObjectCount 13001
86 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
87 <div class="directive-section"><h2><a name="MCacheMaxObjectSize" id="MCacheMaxObjectSize">MCacheMaxObjectSize</a> <a name="mcachemaxobjectsize" id="mcachemaxobjectsize">Directive</a></h2>
88 <table class="directive">
89 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum size (in bytes) of a document allowed in the
91 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MCacheMaxObjectSize <var>bytes</var></code></td></tr>
92 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MCacheMaxObjectSize 10000</code></td></tr>
93 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
94 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
95 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_mem_cache</td></tr>
97 <p>The <code class="directive">MCacheMaxObjectSize</code> directive sets the
98 maximum allowable size, in bytes, of a document for it to be considered
101 <div class="example"><h3>Example</h3><p><code>
102 MCacheMaxObjectSize 6400000
105 <div class="note"><h3>Note</h3>
106 <p>The value of <code class="directive">MCacheMaxObjectSize</code> must be
107 greater than the value specified by the <code class="directive"><a href="#mcacheminobjectsize">MCacheMinObjectSize</a></code> directive.</p>
111 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
112 <div class="directive-section"><h2><a name="MCacheMaxStreamingBuffer" id="MCacheMaxStreamingBuffer">MCacheMaxStreamingBuffer</a> <a name="mcachemaxstreamingbuffer" id="mcachemaxstreamingbuffer">Directive</a></h2>
113 <table class="directive">
114 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum amount of a streamed response to buffer in memory
115 before declaring the response uncacheable</td></tr>
116 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MCacheMaxStreamingBuffer <var>size_in_bytes</var></code></td></tr>
117 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MCacheMaxStreamingBuffer the smaller of 100000 or MCacheMaxObjectSize</code></td></tr>
118 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
119 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
120 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_mem_cache</td></tr>
122 <p>The <code class="directive">MCacheMaxStreamingBuffer</code> directive
123 specifies the maximum number of bytes of a streamed response to
124 buffer before deciding that the response is too big to cache.
125 A streamed response is one in which the entire content is not
126 immediately available and in which the <code>Content-Length</code>
127 may not be known. Sources of streaming responses include proxied
128 responses and the output of CGI scripts. By default, a streamed
129 response will <em>not</em> be cached unless it has a
130 <code>Content-Length</code> header. The reason for this is to
131 avoid using a large amount of memory to buffer a partial response
132 that might end up being too large to fit in the cache.
133 The <code class="directive">MCacheMaxStreamingBuffer</code> directive allows
134 buffering of streamed responses that don't contain a
135 <code>Content-Length</code> up to the specified maximum amount of
136 space. If the maximum buffer space is reached, the buffered
137 content is discarded and the attempt to cache is abandoned.</p>
139 <div class="note"><h3>Note:</h3>
140 <p>Using a nonzero value for <code class="directive">MCacheMaxStreamingBuffer</code>
141 will not delay the transmission of the response to the client.
142 As soon as <code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code> copies a block of streamed
143 content into a buffer, it sends the block on to the next output
144 filter for delivery to the client.</p>
147 <div class="example"><p><code>
148 # Enable caching of streamed responses up to 64KB:<br />
149 MCacheMaxStreamingBuffer 65536
153 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
154 <div class="directive-section"><h2><a name="MCacheMinObjectSize" id="MCacheMinObjectSize">MCacheMinObjectSize</a> <a name="mcacheminobjectsize" id="mcacheminobjectsize">Directive</a></h2>
155 <table class="directive">
156 <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
158 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MCacheMinObjectSize <var>bytes</var></code></td></tr>
159 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MCacheMinObjectSize 0</code></td></tr>
160 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
161 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
162 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_mem_cache</td></tr>
164 <p>The <code class="directive">MCacheMinObjectSize</code> directive sets the
165 minimum size in bytes of a document for it to be considered
168 <div class="example"><h3>Example</h3><p><code>
169 MCacheMinObjectSize 10000
173 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
174 <div class="directive-section"><h2><a name="MCacheRemovalAlgorithm" id="MCacheRemovalAlgorithm">MCacheRemovalAlgorithm</a> <a name="mcacheremovalalgorithm" id="mcacheremovalalgorithm">Directive</a></h2>
175 <table class="directive">
176 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The algorithm used to select documents for removal from the
178 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MCacheRemovalAlgorithm LRU|GDSF</code></td></tr>
179 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MCacheRemovalAlgorithm GDSF</code></td></tr>
180 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
181 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
182 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_mem_cache</td></tr>
184 <p>The <code class="directive">MCacheRemovalAlgorithm</code> directive specifies
185 the algorithm used to select documents for removal from the cache.
186 Two choices are available:</p>
189 <dt><code>LRU</code> (Least Recently Used)</dt>
190 <dd><code>LRU</code> removes the documents that have not been accessed
191 for the longest time.</dd>
193 <dt><code>GDSF</code> (GreadyDual-Size)</dt>
194 <dd><code>GDSF</code> assigns a priority to cached documents based
195 on the cost of a cache miss and the size of the document. Documents
196 with the lowest priority are removed first.</dd>
199 <div class="example"><h3>Example</h3><p><code>
200 MCacheRemovalAlgorithm GDSF<br />
201 MCacheRemovalAlgorithm LRU
205 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
206 <div class="directive-section"><h2><a name="MCacheSize" id="MCacheSize">MCacheSize</a> <a name="mcachesize" id="mcachesize">Directive</a></h2>
207 <table class="directive">
208 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum amount of memory used by the cache in
210 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MCacheSize <var>KBytes</var></code></td></tr>
211 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MCacheSize 100</code></td></tr>
212 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
213 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
214 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_mem_cache</td></tr>
216 <p>The <code class="directive">MCacheSize</code> directive sets the maximum
217 amount of memory to be used by the cache, in KBytes (1024-byte units).
218 If a new object needs to be inserted in the cache and the size of the
219 object is greater than the remaining memory, objects will be removed
220 until the new object can be cached. The object to be removed is
221 selected using the algorithm specified by <code class="directive"><a href="#mcacheremovalalgorithm">MCacheRemovalAlgorithm</a></code>.</p>
223 <div class="example"><h3>Example</h3><p><code>
227 <div class="note"><h3>Note</h3>
228 <p>The <code class="directive">MCacheSize</code> value must be greater than
229 the value specified by the <code class="directive"><a href="#mcachemaxobjectsize">MCacheMaxObjectSize</a></code> directive.</p>
234 <div class="bottomlang">
235 <p><span>Available Languages: </span><a href="../en/mod/mod_mem_cache.html" title="English"> en </a> |
236 <a href="../ja/mod/mod_mem_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
237 <a href="../ko/mod/mod_mem_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
238 </div><div id="footer">
239 <p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
240 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>