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11 (the "License"); you may not use this file except in compliance with
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14 http://www.apache.org/licenses/LICENSE-2.0
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23 <modulesynopsis metafile="mod_cache.xml.meta">
25 <name>mod_cache</name>
26 <description>Content cache keyed to URIs.</description>
27 <status>Extension</status>
28 <sourcefile>mod_cache.c</sourcefile>
29 <identifier>cache_module</identifier>
32 <note type="warning">This module should be used with care and
33 can be used to circumvent <directive
34 module="mod_authz_host">Allow</directive> and <directive
35 module="mod_authz_host">Deny</directive> directives. You
36 should not enable caching for any content to which you wish
37 to limit access by client host name, address or environment
40 <p><module>mod_cache</module> implements an <a
41 href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a> compliant HTTP
42 content cache that can be used to cache either local or proxied content.
43 <module>mod_cache</module> requires the services of one or more storage
44 management modules. Two storage management modules are included in
45 the base Apache distribution:</p>
47 <dt><module>mod_disk_cache</module></dt>
48 <dd>implements a disk based storage manager.</dd>
50 <dt><module>mod_mem_cache</module></dt>
51 <dd>implements a memory based storage manager.
52 <module>mod_mem_cache</module> can be configured to operate in two
53 modes: caching open file descriptors or caching objects in heap storage.
54 <module>mod_mem_cache</module> can be used to cache locally generated content
55 or to cache backend server content for <module>mod_proxy</module> when
56 configured using <directive module="mod_proxy">ProxyPass</directive>
57 (aka <dfn>reverse proxy</dfn>)</dd>
60 <p>Content is stored in and retrieved from the cache using URI based keys. Content with
61 access protection is not cached.</p>
62 <p>Further details, discussion, and examples, are provided in the
63 <a href="../caching.html">Caching Guide</a>.</p>
65 <seealso><a href="../caching.html">Caching Guide</a></seealso>
67 <section id="related"><title>Related Modules and Directives</title>
70 <module>mod_disk_cache</module>
71 <module>mod_mem_cache</module>
74 <directive module="mod_disk_cache">CacheRoot</directive>
75 <directive module="mod_disk_cache">CacheDirLevels</directive>
76 <directive module="mod_disk_cache">CacheDirLength</directive>
77 <directive module="mod_disk_cache">CacheMinFileSize</directive>
78 <directive module="mod_disk_cache">CacheMaxFileSize</directive>
79 <directive module="mod_mem_cache">MCacheSize</directive>
80 <directive module="mod_mem_cache">MCacheMaxObjectCount</directive>
81 <directive module="mod_mem_cache">MCacheMinObjectSize</directive>
82 <directive module="mod_mem_cache">MCacheMaxObjectSize</directive>
83 <directive module="mod_mem_cache">MCacheRemovalAlgorithm</directive>
84 <directive module="mod_mem_cache">MCacheMaxStreamingBuffer</directive>
89 <section id="sampleconf"><title>Sample Configuration</title>
90 <example><title>Sample httpd.conf</title>
92 # Sample Cache Configuration<br />
94 LoadModule cache_module modules/mod_cache.so<br />
96 <IfModule mod_cache.c><br />
98 #LoadModule disk_cache_module modules/mod_disk_cache.so<br />
99 # If you want to use mod_disk_cache instead of mod_mem_cache,<br />
100 # uncomment the line above and comment out the LoadModule line below.<br />
101 <IfModule mod_disk_cache.c><br />
103 CacheRoot c:/cacheroot<br />
104 CacheEnable disk /<br />
105 CacheDirLevels 5<br />
106 CacheDirLength 3<br />
108 </IfModule> <br />
110 LoadModule mem_cache_module modules/mod_mem_cache.so<br />
111 <IfModule mod_mem_cache.c><br />
113 CacheEnable mem /<br />
114 MCacheSize 4096<br />
115 MCacheMaxObjectCount 100<br />
116 MCacheMinObjectSize 1<br />
117 MCacheMaxObjectSize 2048<br />
119 </IfModule><br />
121 # When acting as a proxy, don't cache the list of security updates<br />
122 CacheDisable http://security.update.server/update-list/<br />
129 <name>CacheEnable</name>
130 <description>Enable caching of specified URLs using a specified storage
131 manager</description>
132 <syntax>CacheEnable <var>cache_type</var> <var>url-string</var></syntax>
133 <contextlist><context>server config</context><context>virtual host</context>
137 <p>The <directive>CacheEnable</directive> directive instructs
138 <module>mod_cache</module> to cache urls at or below
139 <var>url-string</var>. The cache storage manager is specified with the
140 <var>cache_type</var> argument. <var>cache_type</var> <code> mem</code>
141 instructs <module>mod_cache</module> to use the memory based storage
142 manager implemented by <module>mod_mem_cache</module>.
143 <var>cache_type</var> <code>disk</code> instructs
144 <module>mod_cache</module> to use the disk based storage manager
145 implemented by <module>mod_disk_cache</module>.
146 <var>cache_type</var> <code>fd</code> instructs
147 <module>mod_cache</module> to use the file descriptor cache implemented
148 by <module>mod_mem_cache</module>.</p>
149 <p>In the event that the URL space overlaps between different
150 <directive>CacheEnable</directive> directives (as in the example below),
151 each possible storage manager will be run until the first one that
152 actually processes the request. The order in which the storage managers are
153 run is determined by the order of the <directive>CacheEnable</directive>
154 directives in the configuration file.</p>
157 CacheEnable mem /manual<br />
158 CacheEnable fd /images<br />
159 CacheEnable disk /<br />
162 <p>When acting as a forward proxy server, <var>url-string</var> can
163 also be used to specify remote sites and proxy protocols which
164 caching should be enabled for.</p>
167 # Cache proxied url's<br />
168 CacheEnable disk /<br /><br />
169 # Cache FTP-proxied url's<br />
170 CacheEnable disk ftp://<br /><br />
171 # Cache content from www.apache.org<br />
172 CacheEnable disk http://www.apache.org/<br />
179 <name>CacheDisable</name>
180 <description>Disable caching of specified URLs</description>
181 <syntax>CacheDisable <var> url-string</var></syntax>
182 <contextlist><context>server config</context><context>virtual host</context>
186 <p>The <directive>CacheDisable</directive> directive instructs
187 <module>mod_cache</module> to <em>not</em> cache urls at or below
188 <var>url-string</var>.</p>
190 <example><title>Example</title>
191 CacheDisable /local_files
197 <name>CacheMaxExpire</name>
198 <description>The maximum time in seconds to cache a document</description>
199 <syntax>CacheMaxExpire <var>seconds</var></syntax>
200 <default>CacheMaxExpire 86400 (one day)</default>
201 <contextlist><context>server config</context><context>virtual host</context>
205 <p>The <directive>CacheMaxExpire</directive> directive specifies the maximum number of
206 seconds for which cachable HTTP documents will be retained without checking the origin
207 server. Thus, documents will be out of date at most this number of seconds. This maximum
208 value is enforced even if an expiry date was supplied with the document.</p>
211 CacheMaxExpire 604800
217 <name>CacheMinExpire</name>
218 <description>The minimum time in seconds to cache a document</description>
219 <syntax>CacheMinExpire <var>seconds</var></syntax>
220 <default>CacheMinExpire 0</default>
221 <contextlist><context>server config</context><context>virtual host</context>
225 <p>The <directive>CacheMinExpire</directive> directive specifies the minimum number of
226 seconds for which cachable HTTP documents will be retained without checking the origin
227 server. This is only used if no valid expire time was supplied with the document.</p>
237 <name>CacheDefaultExpire</name>
238 <description>The default duration to cache a document when no expiry date is specified.</description>
239 <syntax>CacheDefaultExpire <var>seconds</var></syntax>
240 <default>CacheDefaultExpire 3600 (one hour)</default>
241 <contextlist><context>server config</context><context>virtual host</context>
245 <p>The <directive>CacheDefaultExpire</directive> directive specifies a default time,
246 in seconds, to cache a document if neither an expiry date nor last-modified date are provided
247 with the document. The value specified with the <directive>CacheMaxExpire</directive>
248 directive does <em>not</em> override this setting.</p>
251 CacheDefaultExpire 86400
257 <name>CacheIgnoreNoLastMod</name>
258 <description>Ignore the fact that a response has no Last Modified
259 header.</description>
260 <syntax>CacheIgnoreNoLastMod On|Off</syntax>
261 <default>CacheIgnoreNoLastMod Off</default>
262 <contextlist><context>server config</context><context>virtual host</context>
266 <p>Ordinarily, documents without a last-modified date are not cached.
267 Under some circumstances the last-modified date is removed (during
268 <module>mod_include</module> processing for example) or not provided
269 at all. The <directive>CacheIgnoreNoLastMod</directive> directive
270 provides a way to specify that documents without last-modified dates
271 should be considered for caching, even without a last-modified date.
272 If neither a last-modified date nor an expiry date are provided with
273 the document then the value specified by the
274 <directive>CacheDefaultExpire</directive> directive will be used to
275 generate an expiration date.</p>
278 CacheIgnoreNoLastMod On
284 <name>CacheIgnoreCacheControl</name>
285 <description>Ignore request to not serve cached content to client</description>
286 <syntax>CacheIgnoreCacheControl On|Off</syntax>
287 <default>CacheIgnoreCacheControl Off</default>
288 <contextlist><context>server config</context><context>virtual host</context>
292 <p>Ordinarily, requests containing a Cache-Control: no-cache or
293 Pragma: no-cache header value will not be served from the cache. The
294 <directive>CacheIgnoreCacheControl</directive> directive allows this
295 behavior to be overridden. <directive>CacheIgnoreCacheControl</directive>
296 On tells the server to attempt to serve the resource from the cache even
297 if the request contains no-cache header values. Resources requiring
298 authorization will <em>never</em> be cached.</p>
301 CacheIgnoreCacheControl On
304 <note type="warning"><title>Warning:</title>
305 This directive will allow serving from the cache even if the client has
306 requested that the document not be served from the cache. This might
307 result in stale content being served.
310 <seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>
311 <seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>
315 <name>CacheLastModifiedFactor</name>
316 <description>The factor used to compute an expiry date based on the
317 LastModified date.</description>
318 <syntax>CacheLastModifiedFactor <var>float</var></syntax>
319 <default>CacheLastModifiedFactor 0.1</default>
320 <contextlist><context>server config</context><context>virtual host</context>
324 <p>In the event that a document does not provide an expiry date but does
325 provide a last-modified date, an expiry date can be calculated based on
326 the time since the document was last modified. The
327 <directive>CacheLastModifiedFactor</directive> directive specifies a
328 <var>factor</var> to be used in the generation of this expiry date
329 according to the following formula:
331 <code>expiry-period = time-since-last-modified-date * <var>factor</var>
332 expiry-date = current-date + expiry-period</code>
334 For example, if the document was last modified 10 hours ago, and
335 <var>factor</var> is 0.1 then the expiry-period will be set to
336 10*0.1 = 1 hour. If the current time was 3:00pm then the computed
337 expiry-date would be 3:00pm + 1hour = 4:00pm.
339 If the expiry-period would be longer than that set by
340 <directive>CacheMaxExpire</directive>, then the latter takes
344 CacheLastModifiedFactor 0.5
350 <name>CacheIgnoreHeaders</name>
351 <description>Do not store the given HTTP header(s) in the cache.
353 <syntax>CacheIgnoreHeaders <var>header-string</var> [<var>header-string</var>] ...</syntax>
354 <default>CacheIgnoreHeaders None</default>
355 <contextlist><context>server config</context><context>virtual host</context>
359 <p>According to RFC 2616, hop-by-hop HTTP headers are not stored in
360 the cache. The following HTTP headers are hop-by-hop headers and thus
361 do not get stored in the cache in <em>any</em> case regardless of the
362 setting of <directive>CacheIgnoreHeaders</directive>:</p>
365 <li><code>Connection</code></li>
366 <li><code>Keep-Alive</code></li>
367 <li><code>Proxy-Authenticate</code></li>
368 <li><code>Proxy-Authorization</code></li>
369 <li><code>TE</code></li>
370 <li><code>Trailers</code></li>
371 <li><code>Transfer-Encoding</code></li>
372 <li><code>Upgrade</code></li>
375 <p><directive>CacheIgnoreHeaders</directive> specifies additional HTTP
376 headers that should not to be stored in the cache. For example, it makes
377 sense in some cases to prevent cookies from being stored in the cache.</p>
379 <p><directive>CacheIgnoreHeaders</directive> takes a space separated list
380 of HTTP headers that should not be stored in the cache. If only hop-by-hop
381 headers not should be stored in the cache (the RFC 2616 compliant
382 behaviour), <directive>CacheIgnoreHeaders</directive> can be set to
383 <code>None</code>.</p>
385 <example><title>Example 1</title>
386 CacheIgnoreHeaders Set-Cookie
389 <example><title>Example 2</title>
390 CacheIgnoreHeaders None
393 <note type="warning"><title>Warning:</title>
394 If headers like <code>Expires</code> which are needed for proper cache
395 management are not stored due to a
396 <directive>CacheIgnoreHeaders</directive> setting, the behaviour of
397 mod_cache is undefined.
403 <name>CacheStorePrivate</name>
404 <description>Attempt to cache responses that the server has marked as private</description>
405 <syntax>CacheStorePrivate On|Off</syntax>
406 <default>CacheStorePrivate Off</default>
407 <contextlist><context>server config</context><context>virtual host</context>
411 <p>Ordinarily, responses with Cache-Control: private header values will not
412 be stored in the cache. The <directive>CacheStorePrivate</directive>
413 directive allows this behavior to be overridden.
414 <directive>CacheStorePrivate</directive> On
415 tells the server to attempt to cache the resource even if it contains
416 private header values. Resources requiring authorization will
417 <em>never</em> be cached.</p>
423 <note type="warning"><title>Warning:</title>
424 This directive will allow caching even if the upstream server has
425 requested that the resource not be cached. This directive is only
426 ideal for a 'private' cache.
429 <seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>
430 <seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>
434 <name>CacheStoreNoStore</name>
435 <description>Attempt to cache requests or responses that have been marked as no-store.</description>
436 <syntax>CacheStoreNoStore On|Off</syntax>
437 <default>CacheStoreNoStore Off</default>
438 <contextlist><context>server config</context><context>virtual host</context>
442 <p>Ordinarily, requests or responses with Cache-Control: no-store header
443 values will not be stored in the cache. The
444 <directive>CacheStoreNoCache</directive> directive allows this
445 behavior to be overridden. <directive>CacheStoreNoCache</directive> On
446 tells the server to attempt to cache the resource even if it contains
447 no-store header values. Resources requiring authorization will
448 <em>never</em> be cached.</p>
454 <note type="warning"><title>Warning:</title>
455 As described in RFC 2616, the no-store directive is intended to
456 "prevent the inadvertent release or retention of sensitive information
457 (for example, on backup tapes)." Enabling this option could store
458 sensitive information in the cache. You are hereby warned.
461 <seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>
462 <seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>