2 <!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
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4 <!-- $LastChangedRevision$ -->
7 Copyright 2002-2005 The Apache Software Foundation or its licensors, as
10 Licensed under the Apache License, Version 2.0 (the "License");
11 you may not use this file except in compliance with the License.
12 You may obtain a copy of the License at
14 http://www.apache.org/licenses/LICENSE-2.0
16 Unless required by applicable law or agreed to in writing, software
17 distributed under the License is distributed on an "AS IS" BASIS,
18 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
19 See the License for the specific language governing permissions and
20 limitations under the License.
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>
64 <section id="related"><title>Related Modules and Directives</title>
67 <module>mod_disk_cache</module>
68 <module>mod_mem_cache</module>
71 <directive module="mod_disk_cache">CacheRoot</directive>
72 <directive module="mod_disk_cache">CacheSize</directive>
73 <directive module="mod_disk_cache">CacheDirLevels</directive>
74 <directive module="mod_disk_cache">CacheDirLength</directive>
75 <directive module="mod_disk_cache">CacheMinFileSize</directive>
76 <directive module="mod_disk_cache">CacheMaxFileSize</directive>
77 <directive module="mod_mem_cache">MCacheSize</directive>
78 <directive module="mod_mem_cache">MCacheMaxObjectCount</directive>
79 <directive module="mod_mem_cache">MCacheMinObjectSize</directive>
80 <directive module="mod_mem_cache">MCacheMaxObjectSize</directive>
81 <directive module="mod_mem_cache">MCacheRemovalAlgorithm</directive>
82 <directive module="mod_mem_cache">MCacheMaxStreamingBuffer</directive>
87 <section id="sampleconf"><title>Sample Configuration</title>
88 <example><title>Sample httpd.conf</title>
90 # Sample Cache Configuration<br />
92 LoadModule cache_module modules/mod_cache.so<br />
94 <IfModule mod_cache.c><br />
96 #LoadModule disk_cache_module modules/mod_disk_cache.so<br />
97 # If you want to use mod_disk_cache instead of mod_mem_cache,<br />
98 # uncomment the line above and comment out the LoadModule line below.<br />
99 <IfModule mod_disk_cache.c><br />
101 CacheRoot c:/cacheroot<br />
102 CacheEnable disk /<br />
103 CacheDirLevels 5<br />
104 CacheDirLength 3<br />
106 </IfModule> <br />
108 LoadModule mem_cache_module modules/mod_mem_cache.so<br />
109 <IfModule mod_mem_cache.c><br />
111 CacheEnable mem /<br />
112 MCacheSize 4096<br />
113 MCacheMaxObjectCount 100<br />
114 MCacheMinObjectSize 1<br />
115 MCacheMaxObjectSize 2048<br />
117 </IfModule><br />
119 # When acting as a proxy, don't cache the list of security updates<br />
120 CacheDisable http://security.update.server/update-list/<br />
127 <name>CacheEnable</name>
128 <description>Enable caching of specified URLs using a specified storage
129 manager</description>
130 <syntax>CacheEnable <var>cache_type</var> <var>url-string</var></syntax>
131 <contextlist><context>server config</context><context>virtual host</context>
135 <p>The <directive>CacheEnable</directive> directive instructs
136 <module>mod_cache</module> to cache urls at or below
137 <var>url-string</var>. The cache storage manager is specified with the
138 <var>cache_type</var> argument. <var>cache_type</var> <code> mem</code>
139 instructs <module>mod_cache</module> to use the memory based storage
140 manager implemented by <module>mod_mem_cache</module>.
141 <var>cache_type</var> <code>disk</code> instructs
142 <module>mod_cache</module> to use the disk based storage manager
143 implemented by <module>mod_disk_cache</module>.
144 <var>cache_type</var> <code>fd</code> instructs
145 <module>mod_cache</module> to use the file descriptor cache implemented
146 by <module>mod_mem_cache</module>.</p>
147 <p>In the event that the URL space overlaps between different
148 <directive>CacheEnable</directive> directives (as in the example below),
149 each possible storage manager will be run until the first one that
150 actually processes the request. The order in which the storage managers are
151 run is determined by the order of the <directive>CacheEnable</directive>
152 directives in the configuration file.</p>
155 CacheEnable mem /manual<br />
156 CacheEnable fd /images<br />
157 CacheEnable disk /<br />
160 <p>When acting as a forward proxy server, <var>url-string</var> can
161 also be used to specify remote sites and proxy protocols which
162 caching should be enabled for.</p>
165 # Cache proxied url's<br />
166 CacheEnable disk /<br /><br />
167 # Cache FTP-proxied url's<br />
168 CacheEnable disk ftp://<br /><br />
169 # Cache content from www.apache.org<br />
170 CacheEnable disk http://www.apache.org/<br />
177 <name>CacheDisable</name>
178 <description>Disable caching of specified URLs</description>
179 <syntax>CacheDisable <var> url-string</var></syntax>
180 <contextlist><context>server config</context><context>virtual host</context>
184 <p>The <directive>CacheDisable</directive> directive instructs
185 <module>mod_cache</module> to <em>not</em> cache urls at or below
186 <var>url-string</var>.</p>
188 <example><title>Example</title>
189 CacheDisable /local_files
195 <name>CacheMaxExpire</name>
196 <description>The maximum time in seconds to cache a document</description>
197 <syntax>CacheMaxExpire <var>seconds</var></syntax>
198 <default>CacheMaxExpire 86400 (one day)</default>
199 <contextlist><context>server config</context><context>virtual host</context>
203 <p>The <directive>CacheMaxExpire</directive> directive specifies the maximum number of
204 seconds for which cachable HTTP documents will be retained without checking the origin
205 server. Thus, documents will be out of date at most this number of seconds. This maximum
206 value is enforced even if an expiry date was supplied with the document.</p>
209 CacheMaxExpire 604800
215 <name>CacheDefaultExpire</name>
216 <description>The default duration to cache a document when no expiry date is specified.</description>
217 <syntax>CacheDefaultExpire <var>seconds</var></syntax>
218 <default>CacheDefaultExpire 3600 (one hour)</default>
219 <contextlist><context>server config</context><context>virtual host</context>
223 <p>The <directive>CacheDefaultExpire</directive> directive specifies a default time,
224 in seconds, to cache a document if neither an expiry date nor last-modified date are provided
225 with the document. The value specified with the <directive>CacheMaxExpire</directive>
226 directive does <em>not</em> override this setting.</p>
229 CacheDefaultExpire 86400
235 <name>CacheIgnoreNoLastMod</name>
236 <description>Ignore the fact that a response has no Last Modified
237 header.</description>
238 <syntax>CacheIgnoreNoLastMod On|Off</syntax>
239 <default>CacheIgnoreNoLastMod Off</default>
240 <contextlist><context>server config</context><context>virtual host</context>
244 <p>Ordinarily, documents without a last-modified date are not cached.
245 Under some circumstances the last-modified date is removed (during
246 <module>mod_include</module> processing for example) or not provided
247 at all. The <directive>CacheIgnoreNoLastMod</directive> directive
248 provides a way to specify that documents without last-modified dates
249 should be considered for caching, even without a last-modified date.
250 If neither a last-modified date nor an expiry date are provided with
251 the document then the value specified by the
252 <directive>CacheDefaultExpire</directive> directive will be used to
253 generate an expiration date.</p>
256 CacheIgnoreNoLastMod On
262 <name>CacheIgnoreCacheControl</name>
263 <description>Ignore request to not serve cached content to client</description>
264 <syntax>CacheIgnoreCacheControl On|Off</syntax>
265 <default>CacheIgnoreCacheControl Off</default>
266 <contextlist><context>server config</context><context>virtual host</context>
270 <p>Ordinarily, requests containing a Cache-Control: no-cache or
271 Pragma: no-cache header value will not be served from the cache. The
272 <directive>CacheIgnoreCacheControl</directive> directive allows this
273 behavior to be overridden. <directive>CacheIgnoreCacheControl</directive>
274 On tells the server to attempt to serve the resource from the cache even
275 if the request contains no-cache header values. Resources requiring
276 authorization will <em>never</em> be cached.</p>
279 CacheIgnoreCacheControl On
282 <note type="warning"><title>Warning:</title>
283 This directive will allow serving from the cache even if the client has
284 requested that the document not be served from the cache. This might
285 result in stale content being served.
288 <seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>
289 <seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>
293 <name>CacheLastModifiedFactor</name>
294 <description>The factor used to compute an expiry date based on the
295 LastModified date.</description>
296 <syntax>CacheLastModifiedFactor <var>float</var></syntax>
297 <default>CacheLastModifiedFactor 0.1</default>
298 <contextlist><context>server config</context><context>virtual host</context>
302 <p>In the event that a document does not provide an expiry date but does
303 provide a last-modified date, an expiry date can be calculated based on
304 the time since the document was last modified. The
305 <directive>CacheLastModifiedFactor</directive> directive specifies a
306 <var>factor</var> to be used in the generation of this expiry date
307 according to the following formula:
309 <code>expiry-period = time-since-last-modified-date * <var>factor</var>
310 expiry-date = current-date + expiry-period</code>
312 For example, if the document was last modified 10 hours ago, and
313 <var>factor</var> is 0.1 then the expiry-period will be set to
314 10*0.1 = 1 hour. If the current time was 3:00pm then the computed
315 expiry-date would be 3:00pm + 1hour = 4:00pm.
317 If the expiry-period would be longer than that set by
318 <directive>CacheMaxExpire</directive>, then the latter takes
322 CacheLastModifiedFactor 0.5
328 <name>CacheIgnoreHeaders</name>
329 <description>Do not store the given HTTP header(s) in the cache.
331 <syntax>CacheIgnoreHeaders <var>header-string</var> [<var>header-string</var>] ...</syntax>
332 <default>CacheIgnoreHeaders None</default>
333 <contextlist><context>server config</context><context>virtual host</context>
337 <p>According to RFC 2616, hop-by-hop HTTP headers are not stored in
338 the cache. The following HTTP headers are hop-by-hop headers and thus
339 do not get stored in the cache in <em>any</em> case regardless of the
340 setting of <directive>CacheIgnoreHeaders</directive>:</p>
343 <li><code>Connection</code></li>
344 <li><code>Keep-Alive</code></li>
345 <li><code>Proxy-Authenticate</code></li>
346 <li><code>Proxy-Authorization</code></li>
347 <li><code>TE</code></li>
348 <li><code>Trailers</code></li>
349 <li><code>Transfer-Encoding</code></li>
350 <li><code>Upgrade</code></li>
353 <p><directive>CacheIgnoreHeaders</directive> specifies additional HTTP
354 headers that should not to be stored in the cache. For example, it makes
355 sense in some cases to prevent cookies from being stored in the cache.</p>
357 <p><directive>CacheIgnoreHeaders</directive> takes a space separated list
358 of HTTP headers that should not be stored in the cache. If only hop-by-hop
359 headers not should be stored in the cache (the RFC 2616 compliant
360 behaviour), <directive>CacheIgnoreHeaders</directive> can be set to
361 <code>None</code>.</p>
363 <example><title>Example 1</title>
364 CacheIgnoreHeaders Set-Cookie
367 <example><title>Example 2</title>
368 CacheIgnoreHeaders None
371 <note type="warning"><title>Warning:</title>
372 If headers like <code>Expires</code> which are needed for proper cache
373 management are not stored due to a
374 <directive>CacheIgnoreHeaders</directive> setting, the behaviour of
375 mod_cache is undefined.
381 <name>CacheStorePrivate</name>
382 <description>Attempt to cache responses that the server has marked as private</description>
383 <syntax>CacheStorePrivate On|Off</syntax>
384 <default>CacheStorePrivate Off</default>
385 <contextlist><context>server config</context><context>virtual host</context>
389 <p>Ordinarily, responses with Cache-Control: private header values will not
390 be stored in the cache. The <directive>CacheStorePrivate</directive>
391 directive allows this behavior to be overridden.
392 <directive>CacheStorePrivate</directive> On
393 tells the server to attempt to cache the resource even if it contains
394 private header values. Resources requiring authorization will
395 <em>never</em> be cached.</p>
401 <note type="warning"><title>Warning:</title>
402 This directive will allow caching even if the upstream server has
403 requested that the resource not be cached. This directive is only
404 ideal for a 'private' cache.
407 <seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>
408 <seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>
412 <name>CacheStoreNoStore</name>
413 <description>Attempt to cache requests or responses that have been marked as no-store.</description>
414 <syntax>CacheStoreNoStore On|Off</syntax>
415 <default>CacheStoreNoStore Off</default>
416 <contextlist><context>server config</context><context>virtual host</context>
420 <p>Ordinarily, requests or responses with Cache-Control: no-store header
421 values will not be stored in the cache. The
422 <directive>CacheStoreNoCache</directive> directive allows this
423 behavior to be overridden. <directive>CacheStoreNoCache</directive> On
424 tells the server to attempt to cache the resource even if it contains
425 no-store header values. Resources requiring authorization will
426 <em>never</em> be cached.</p>
432 <note type="warning"><title>Warning:</title>
433 As described in RFC 2616, the no-store directive is intended to
434 "prevent the inadvertent release or retention of sensitive information
435 (for example, on backup tapes)." Enabling this option could store
436 sensitive information in the cache. You are hereby warned.
439 <seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>
440 <seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>