2 <!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
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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">CacheDirLevels</directive>
73 <directive module="mod_disk_cache">CacheDirLength</directive>
74 <directive module="mod_disk_cache">CacheMinFileSize</directive>
75 <directive module="mod_disk_cache">CacheMaxFileSize</directive>
76 <directive module="mod_mem_cache">MCacheSize</directive>
77 <directive module="mod_mem_cache">MCacheMaxObjectCount</directive>
78 <directive module="mod_mem_cache">MCacheMinObjectSize</directive>
79 <directive module="mod_mem_cache">MCacheMaxObjectSize</directive>
80 <directive module="mod_mem_cache">MCacheRemovalAlgorithm</directive>
81 <directive module="mod_mem_cache">MCacheMaxStreamingBuffer</directive>
86 <section id="sampleconf"><title>Sample Configuration</title>
87 <example><title>Sample httpd.conf</title>
89 # Sample Cache Configuration<br />
91 LoadModule cache_module modules/mod_cache.so<br />
93 <IfModule mod_cache.c><br />
95 #LoadModule disk_cache_module modules/mod_disk_cache.so<br />
96 # If you want to use mod_disk_cache instead of mod_mem_cache,<br />
97 # uncomment the line above and comment out the LoadModule line below.<br />
98 <IfModule mod_disk_cache.c><br />
100 CacheRoot c:/cacheroot<br />
101 CacheEnable disk /<br />
102 CacheDirLevels 5<br />
103 CacheDirLength 3<br />
105 </IfModule> <br />
107 LoadModule mem_cache_module modules/mod_mem_cache.so<br />
108 <IfModule mod_mem_cache.c><br />
110 CacheEnable mem /<br />
111 MCacheSize 4096<br />
112 MCacheMaxObjectCount 100<br />
113 MCacheMinObjectSize 1<br />
114 MCacheMaxObjectSize 2048<br />
116 </IfModule><br />
118 # When acting as a proxy, don't cache the list of security updates<br />
119 CacheDisable http://security.update.server/update-list/<br />
126 <name>CacheEnable</name>
127 <description>Enable caching of specified URLs using a specified storage
128 manager</description>
129 <syntax>CacheEnable <var>cache_type</var> <var>url-string</var></syntax>
130 <contextlist><context>server config</context><context>virtual host</context>
134 <p>The <directive>CacheEnable</directive> directive instructs
135 <module>mod_cache</module> to cache urls at or below
136 <var>url-string</var>. The cache storage manager is specified with the
137 <var>cache_type</var> argument. <var>cache_type</var> <code> mem</code>
138 instructs <module>mod_cache</module> to use the memory based storage
139 manager implemented by <module>mod_mem_cache</module>.
140 <var>cache_type</var> <code>disk</code> instructs
141 <module>mod_cache</module> to use the disk based storage manager
142 implemented by <module>mod_disk_cache</module>.
143 <var>cache_type</var> <code>fd</code> instructs
144 <module>mod_cache</module> to use the file descriptor cache implemented
145 by <module>mod_mem_cache</module>.</p>
146 <p>In the event that the URL space overlaps between different
147 <directive>CacheEnable</directive> directives (as in the example below),
148 each possible storage manager will be run until the first one that
149 actually processes the request. The order in which the storage managers are
150 run is determined by the order of the <directive>CacheEnable</directive>
151 directives in the configuration file.</p>
154 CacheEnable mem /manual<br />
155 CacheEnable fd /images<br />
156 CacheEnable disk /<br />
159 <p>When acting as a forward proxy server, <var>url-string</var> can
160 also be used to specify remote sites and proxy protocols which
161 caching should be enabled for.</p>
164 # Cache proxied url's<br />
165 CacheEnable disk /<br /><br />
166 # Cache FTP-proxied url's<br />
167 CacheEnable disk ftp://<br /><br />
168 # Cache content from www.apache.org<br />
169 CacheEnable disk http://www.apache.org/<br />
176 <name>CacheDisable</name>
177 <description>Disable caching of specified URLs</description>
178 <syntax>CacheDisable <var> url-string</var></syntax>
179 <contextlist><context>server config</context><context>virtual host</context>
183 <p>The <directive>CacheDisable</directive> directive instructs
184 <module>mod_cache</module> to <em>not</em> cache urls at or below
185 <var>url-string</var>.</p>
187 <example><title>Example</title>
188 CacheDisable /local_files
194 <name>CacheMaxExpire</name>
195 <description>The maximum time in seconds to cache a document</description>
196 <syntax>CacheMaxExpire <var>seconds</var></syntax>
197 <default>CacheMaxExpire 86400 (one day)</default>
198 <contextlist><context>server config</context><context>virtual host</context>
202 <p>The <directive>CacheMaxExpire</directive> directive specifies the maximum number of
203 seconds for which cachable HTTP documents will be retained without checking the origin
204 server. Thus, documents will be out of date at most this number of seconds. This maximum
205 value is enforced even if an expiry date was supplied with the document.</p>
208 CacheMaxExpire 604800
214 <name>CacheMinExpire</name>
215 <description>The minimum time in seconds to cache a document</description>
216 <syntax>CacheMinExpire <var>seconds</var></syntax>
217 <default>CacheMinExpire 0</default>
218 <contextlist><context>server config</context><context>virtual host</context>
222 <p>The <directive>CacheMinExpire</directive> directive specifies the minimum number of
223 seconds for which cachable HTTP documents will be retained without checking the origin
224 server. This is only used if no valid expire time was supplied with the document.</p>
234 <name>CacheDefaultExpire</name>
235 <description>The default duration to cache a document when no expiry date is specified.</description>
236 <syntax>CacheDefaultExpire <var>seconds</var></syntax>
237 <default>CacheDefaultExpire 3600 (one hour)</default>
238 <contextlist><context>server config</context><context>virtual host</context>
242 <p>The <directive>CacheDefaultExpire</directive> directive specifies a default time,
243 in seconds, to cache a document if neither an expiry date nor last-modified date are provided
244 with the document. The value specified with the <directive>CacheMaxExpire</directive>
245 directive does <em>not</em> override this setting.</p>
248 CacheDefaultExpire 86400
254 <name>CacheIgnoreNoLastMod</name>
255 <description>Ignore the fact that a response has no Last Modified
256 header.</description>
257 <syntax>CacheIgnoreNoLastMod On|Off</syntax>
258 <default>CacheIgnoreNoLastMod Off</default>
259 <contextlist><context>server config</context><context>virtual host</context>
263 <p>Ordinarily, documents without a last-modified date are not cached.
264 Under some circumstances the last-modified date is removed (during
265 <module>mod_include</module> processing for example) or not provided
266 at all. The <directive>CacheIgnoreNoLastMod</directive> directive
267 provides a way to specify that documents without last-modified dates
268 should be considered for caching, even without a last-modified date.
269 If neither a last-modified date nor an expiry date are provided with
270 the document then the value specified by the
271 <directive>CacheDefaultExpire</directive> directive will be used to
272 generate an expiration date.</p>
275 CacheIgnoreNoLastMod On
281 <name>CacheIgnoreCacheControl</name>
282 <description>Ignore request to not serve cached content to client</description>
283 <syntax>CacheIgnoreCacheControl On|Off</syntax>
284 <default>CacheIgnoreCacheControl Off</default>
285 <contextlist><context>server config</context><context>virtual host</context>
289 <p>Ordinarily, requests containing a Cache-Control: no-cache or
290 Pragma: no-cache header value will not be served from the cache. The
291 <directive>CacheIgnoreCacheControl</directive> directive allows this
292 behavior to be overridden. <directive>CacheIgnoreCacheControl</directive>
293 On tells the server to attempt to serve the resource from the cache even
294 if the request contains no-cache header values. Resources requiring
295 authorization will <em>never</em> be cached.</p>
298 CacheIgnoreCacheControl On
301 <note type="warning"><title>Warning:</title>
302 This directive will allow serving from the cache even if the client has
303 requested that the document not be served from the cache. This might
304 result in stale content being served.
307 <seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>
308 <seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>
312 <name>CacheLastModifiedFactor</name>
313 <description>The factor used to compute an expiry date based on the
314 LastModified date.</description>
315 <syntax>CacheLastModifiedFactor <var>float</var></syntax>
316 <default>CacheLastModifiedFactor 0.1</default>
317 <contextlist><context>server config</context><context>virtual host</context>
321 <p>In the event that a document does not provide an expiry date but does
322 provide a last-modified date, an expiry date can be calculated based on
323 the time since the document was last modified. The
324 <directive>CacheLastModifiedFactor</directive> directive specifies a
325 <var>factor</var> to be used in the generation of this expiry date
326 according to the following formula:
328 <code>expiry-period = time-since-last-modified-date * <var>factor</var>
329 expiry-date = current-date + expiry-period</code>
331 For example, if the document was last modified 10 hours ago, and
332 <var>factor</var> is 0.1 then the expiry-period will be set to
333 10*0.1 = 1 hour. If the current time was 3:00pm then the computed
334 expiry-date would be 3:00pm + 1hour = 4:00pm.
336 If the expiry-period would be longer than that set by
337 <directive>CacheMaxExpire</directive>, then the latter takes
341 CacheLastModifiedFactor 0.5
347 <name>CacheIgnoreHeaders</name>
348 <description>Do not store the given HTTP header(s) in the cache.
350 <syntax>CacheIgnoreHeaders <var>header-string</var> [<var>header-string</var>] ...</syntax>
351 <default>CacheIgnoreHeaders None</default>
352 <contextlist><context>server config</context><context>virtual host</context>
356 <p>According to RFC 2616, hop-by-hop HTTP headers are not stored in
357 the cache. The following HTTP headers are hop-by-hop headers and thus
358 do not get stored in the cache in <em>any</em> case regardless of the
359 setting of <directive>CacheIgnoreHeaders</directive>:</p>
362 <li><code>Connection</code></li>
363 <li><code>Keep-Alive</code></li>
364 <li><code>Proxy-Authenticate</code></li>
365 <li><code>Proxy-Authorization</code></li>
366 <li><code>TE</code></li>
367 <li><code>Trailers</code></li>
368 <li><code>Transfer-Encoding</code></li>
369 <li><code>Upgrade</code></li>
372 <p><directive>CacheIgnoreHeaders</directive> specifies additional HTTP
373 headers that should not to be stored in the cache. For example, it makes
374 sense in some cases to prevent cookies from being stored in the cache.</p>
376 <p><directive>CacheIgnoreHeaders</directive> takes a space separated list
377 of HTTP headers that should not be stored in the cache. If only hop-by-hop
378 headers not should be stored in the cache (the RFC 2616 compliant
379 behaviour), <directive>CacheIgnoreHeaders</directive> can be set to
380 <code>None</code>.</p>
382 <example><title>Example 1</title>
383 CacheIgnoreHeaders Set-Cookie
386 <example><title>Example 2</title>
387 CacheIgnoreHeaders None
390 <note type="warning"><title>Warning:</title>
391 If headers like <code>Expires</code> which are needed for proper cache
392 management are not stored due to a
393 <directive>CacheIgnoreHeaders</directive> setting, the behaviour of
394 mod_cache is undefined.
400 <name>CacheStorePrivate</name>
401 <description>Attempt to cache responses that the server has marked as private</description>
402 <syntax>CacheStorePrivate On|Off</syntax>
403 <default>CacheStorePrivate Off</default>
404 <contextlist><context>server config</context><context>virtual host</context>
408 <p>Ordinarily, responses with Cache-Control: private header values will not
409 be stored in the cache. The <directive>CacheStorePrivate</directive>
410 directive allows this behavior to be overridden.
411 <directive>CacheStorePrivate</directive> On
412 tells the server to attempt to cache the resource even if it contains
413 private header values. Resources requiring authorization will
414 <em>never</em> be cached.</p>
420 <note type="warning"><title>Warning:</title>
421 This directive will allow caching even if the upstream server has
422 requested that the resource not be cached. This directive is only
423 ideal for a 'private' cache.
426 <seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>
427 <seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>
431 <name>CacheStoreNoStore</name>
432 <description>Attempt to cache requests or responses that have been marked as no-store.</description>
433 <syntax>CacheStoreNoStore On|Off</syntax>
434 <default>CacheStoreNoStore Off</default>
435 <contextlist><context>server config</context><context>virtual host</context>
439 <p>Ordinarily, requests or responses with Cache-Control: no-store header
440 values will not be stored in the cache. The
441 <directive>CacheStoreNoCache</directive> directive allows this
442 behavior to be overridden. <directive>CacheStoreNoCache</directive> On
443 tells the server to attempt to cache the resource even if it contains
444 no-store header values. Resources requiring authorization will
445 <em>never</em> be cached.</p>
451 <note type="warning"><title>Warning:</title>
452 As described in RFC 2616, the no-store directive is intended to
453 "prevent the inadvertent release or retention of sensitive information
454 (for example, on backup tapes)." Enabling this option could store
455 sensitive information in the cache. You are hereby warned.
458 <seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>
459 <seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>