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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 <p><module>mod_cache</module> implements an <a
33 href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a> compliant HTTP
34 content cache that can be used to cache either local or proxied content.
35 <module>mod_cache</module> requires the services of one or more storage
36 management modules. Two storage management modules are included in
37 the base Apache distribution:</p>
39 <dt><module>mod_disk_cache</module></dt>
40 <dd>implements a disk based storage manager.</dd>
42 <dt><module>mod_mem_cache</module></dt>
43 <dd>implements a memory based storage manager.
44 <module>mod_mem_cache</module> can be configured to operate in two
45 modes: caching open file descriptors or caching objects in heap storage.
46 <module>mod_mem_cache</module> can be used to cache locally generated content
47 or to cache backend server content for <module>mod_proxy</module> when
48 configured using <directive module="mod_proxy">ProxyPass</directive>
49 (aka <dfn>reverse proxy</dfn>)</dd>
52 <p>Content is stored in and retrieved from the cache using URI based keys. Content with
53 access protection is not cached.</p>
56 <section id="related"><title>Related Modules and Directives</title>
59 <module>mod_disk_cache</module>
60 <module>mod_mem_cache</module>
63 <directive module="mod_disk_cache">CacheRoot</directive>
64 <directive module="mod_disk_cache">CacheSize</directive>
65 <directive module="mod_disk_cache">CacheDirLevels</directive>
66 <directive module="mod_disk_cache">CacheDirLength</directive>
67 <directive module="mod_disk_cache">CacheMinFileSize</directive>
68 <directive module="mod_disk_cache">CacheMaxFileSize</directive>
69 <directive module="mod_mem_cache">MCacheSize</directive>
70 <directive module="mod_mem_cache">MCacheMaxObjectCount</directive>
71 <directive module="mod_mem_cache">MCacheMinObjectSize</directive>
72 <directive module="mod_mem_cache">MCacheMaxObjectSize</directive>
73 <directive module="mod_mem_cache">MCacheRemovalAlgorithm</directive>
74 <directive module="mod_mem_cache">MCacheMaxStreamingBuffer</directive>
79 <section id="sampleconf"><title>Sample Configuration</title>
80 <example><title>Sample httpd.conf</title>
82 # Sample Cache Configuration<br />
84 LoadModule cache_module modules/mod_cache.so<br />
86 <IfModule mod_cache.c><br />
88 #LoadModule disk_cache_module modules/mod_disk_cache.so<br />
89 # If you want to use mod_disk_cache instead of mod_mem_cache,<br />
90 # uncomment the line above and comment out the LoadModule line below.<br />
91 <IfModule mod_disk_cache.c><br />
93 CacheRoot c:/cacheroot<br />
94 CacheEnable disk /<br />
95 CacheDirLevels 5<br />
96 CacheDirLength 3<br />
98 </IfModule> <br />
100 LoadModule mem_cache_module modules/mod_mem_cache.so<br />
101 <IfModule mod_mem_cache.c><br />
103 CacheEnable mem /<br />
104 MCacheSize 4096<br />
105 MCacheMaxObjectCount 100<br />
106 MCacheMinObjectSize 1<br />
107 MCacheMaxObjectSize 2048<br />
109 </IfModule><br />
111 # When acting as a proxy, don't cache the list of security updates<br />
112 CacheDisable http://security.update.server/update-list/<br />
119 <name>CacheEnable</name>
120 <description>Enable caching of specified URLs using a specified storage
121 manager</description>
122 <syntax>CacheEnable <var>cache_type</var> <var>url-string</var></syntax>
123 <contextlist><context>server config</context><context>virtual host</context>
127 <p>The <directive>CacheEnable</directive> directive instructs
128 <module>mod_cache</module> to cache urls at or below
129 <var>url-string</var>. The cache storage manager is specified with the
130 <var>cache_type</var> argument. <var>cache_type</var> <code> mem</code>
131 instructs <module>mod_cache</module> to use the memory based storage
132 manager implemented by <module>mod_mem_cache</module>.
133 <var>cache_type</var> <code>disk</code> instructs
134 <module>mod_cache</module> to use the disk based storage manager
135 implemented by <module>mod_disk_cache</module>.
136 <var>cache_type</var> <code>fd</code> instructs
137 <module>mod_cache</module> to use the file descriptor cache implemented
138 by <module>mod_mem_cache</module>.</p>
139 <p>In the event that the URL space overlaps between different
140 <directive>CacheEnable</directive> directives (as in the example below),
141 each possible storage manager will be run until the first one that
142 actually processes the request. The order in which the storage managers are
143 run is determined by the order of the <directive>CacheEnable</directive>
144 directives in the configuration file.</p>
147 CacheEnable mem /manual<br />
148 CacheEnable fd /images<br />
149 CacheEnable disk /<br />
152 <p>When acting as a forward proxy server, <var>url-string</var> can
153 also be used to specify remote sites and proxy protocols which
154 caching should be enabled for.</p>
157 # Cache proxied url's<br />
158 CacheEnable disk /<br /><br />
159 # Cache FTP-proxied url's<br />
160 CacheEnable disk ftp://<br /><br />
161 # Cache content from www.apache.org<br />
162 CacheEnable disk http://www.apache.org/<br />
169 <name>CacheDisable</name>
170 <description>Disable caching of specified URLs</description>
171 <syntax>CacheDisable <var> url-string</var></syntax>
172 <contextlist><context>server config</context><context>virtual host</context>
176 <p>The <directive>CacheDisable</directive> directive instructs
177 <module>mod_cache</module> to <em>not</em> cache urls at or below
178 <var>url-string</var>.</p>
180 <example><title>Example</title>
181 CacheDisable /local_files
187 <name>CacheMaxExpire</name>
188 <description>The maximum time in seconds to cache a document</description>
189 <syntax>CacheMaxExpire <var>seconds</var></syntax>
190 <default>CacheMaxExpire 86400 (one day)</default>
191 <contextlist><context>server config</context><context>virtual host</context>
195 <p>The <directive>CacheMaxExpire</directive> directive specifies the maximum number of
196 seconds for which cachable HTTP documents will be retained without checking the origin
197 server. Thus, documents will be out of date at most this number of seconds. This maximum
198 value is enforced even if an expiry date was supplied with the document.</p>
201 CacheMaxExpire 604800
207 <name>CacheDefaultExpire</name>
208 <description>The default duration to cache a document when no expiry date is specified.</description>
209 <syntax>CacheDefaultExpire <var>seconds</var></syntax>
210 <default>CacheDefaultExpire 3600 (one hour)</default>
211 <contextlist><context>server config</context><context>virtual host</context>
215 <p>The <directive>CacheDefaultExpire</directive> directive specifies a default time,
216 in seconds, to cache a document if neither an expiry date nor last-modified date are provided
217 with the document. The value specified with the <directive>CacheMaxExpire</directive>
218 directive does <em>not</em> override this setting.</p>
221 CacheDefaultExpire 86400
227 <name>CacheIgnoreNoLastMod</name>
228 <description>Ignore the fact that a response has no Last Modified
229 header.</description>
230 <syntax>CacheIgnoreNoLastMod On|Off</syntax>
231 <default>CacheIgnoreNoLastMod Off</default>
232 <contextlist><context>server config</context><context>virtual host</context>
236 <p>Ordinarily, documents without a last-modified date are not cached.
237 Under some circumstances the last-modified date is removed (during
238 <module>mod_include</module> processing for example) or not provided
239 at all. The <directive>CacheIgnoreNoLastMod</directive> directive
240 provides a way to specify that documents without last-modified dates
241 should be considered for caching, even without a last-modified date.
242 If neither a last-modified date nor an expiry date are provided with
243 the document then the value specified by the
244 <directive>CacheDefaultExpire</directive> directive will be used to
245 generate an expiration date.</p>
248 CacheIgnoreNoLastMod On
254 <name>CacheIgnoreCacheControl</name>
255 <description>Ignore request to not serve cached content to client</description>
256 <syntax>CacheIgnoreCacheControl On|Off</syntax>
257 <default>CacheIgnoreCacheControl Off</default>
258 <contextlist><context>server config</context><context>virtual host</context>
262 <p>Ordinarily, requests containing a Cache-Control: no-cache or
263 Pragma: no-cache header value will not be served from the cache. The
264 <directive>CacheIgnoreCacheControl</directive> directive allows this
265 behavior to be overridden. <directive>CacheIgnoreCacheControl</directive>
266 On tells the server to attempt to serve the resource from the cache even
267 if the request contains no-cache header values. Resources requiring
268 authorization will <em>never</em> be cached.</p>
271 CacheIgnoreCacheControl On
274 <note type="warning"><title>Warning:</title>
275 This directive will allow serving from the cache even if the client has
276 requested that the document not be served from the cache. This might
277 result in stale content being served.
280 <seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>
281 <seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>
285 <name>CacheLastModifiedFactor</name>
286 <description>The factor used to compute an expiry date based on the
287 LastModified date.</description>
288 <syntax>CacheLastModifiedFactor <var>float</var></syntax>
289 <default>CacheLastModifiedFactor 0.1</default>
290 <contextlist><context>server config</context><context>virtual host</context>
294 <p>In the event that a document does not provide an expiry date but does
295 provide a last-modified date, an expiry date can be calculated based on
296 the time since the document was last modified. The
297 <directive>CacheLastModifiedFactor</directive> directive specifies a
298 <var>factor</var> to be used in the generation of this expiry date
299 according to the following formula:
301 <code>expiry-period = time-since-last-modified-date * <var>factor</var>
302 expiry-date = current-date + expiry-period</code>
304 For example, if the document was last modified 10 hours ago, and
305 <var>factor</var> is 0.1 then the expiry-period will be set to
306 10*0.1 = 1 hour. If the current time was 3:00pm then the computed
307 expiry-date would be 3:00pm + 1hour = 4:00pm.
309 If the expiry-period would be longer than that set by
310 <directive>CacheMaxExpire</directive>, then the latter takes
314 CacheLastModifiedFactor 0.5
320 <name>CacheIgnoreHeaders</name>
321 <description>Do not store the given HTTP header(s) in the cache.
323 <syntax>CacheIgnoreHeaders <var>header-string</var> [<var>header-string</var>] ...</syntax>
324 <default>CacheIgnoreHeaders None</default>
325 <contextlist><context>server config</context><context>virtual host</context>
329 <p>According to RFC 2616, hop-by-hop HTTP headers are not stored in
330 the cache. The following HTTP headers are hop-by-hop headers and thus
331 do not get stored in the cache in <em>any</em> case regardless of the
332 setting of <directive>CacheIgnoreHeaders</directive>:</p>
335 <li><code>Connection</code></li>
336 <li><code>Keep-Alive</code></li>
337 <li><code>Proxy-Authenticate</code></li>
338 <li><code>Proxy-Authorization</code></li>
339 <li><code>TE</code></li>
340 <li><code>Trailers</code></li>
341 <li><code>Transfer-Encoding</code></li>
342 <li><code>Upgrade</code></li>
345 <p><directive>CacheIgnoreHeaders</directive> specifies additional HTTP
346 headers that should not to be stored in the cache. For example, it makes
347 sense in some cases to prevent cookies from being stored in the cache.</p>
349 <p><directive>CacheIgnoreHeaders</directive> takes a space separated list
350 of HTTP headers that should not be stored in the cache. If only hop-by-hop
351 headers not should be stored in the cache (the RFC 2616 compliant
352 behaviour), <directive>CacheIgnoreHeaders</directive> can be set to
353 <code>None</code>.</p>
355 <example><title>Example 1</title>
356 CacheIgnoreHeaders Set-Cookie
359 <example><title>Example 2</title>
360 CacheIgnoreHeaders None
363 <note type="warning"><title>Warning:</title>
364 If headers like <code>Expires</code> which are needed for proper cache
365 management are not stored due to a
366 <directive>CacheIgnoreHeaders</directive> setting, the behaviour of
367 mod_cache is undefined.
373 <name>CacheStorePrivate</name>
374 <description>Attempt to cache responses that the server has marked as private</description>
375 <syntax>CacheStorePrivate On|Off</syntax>
376 <default>CacheStorePrivate Off</default>
377 <contextlist><context>server config</context><context>virtual host</context>
381 <p>Ordinarily, responses with Cache-Control: private header values will not
382 be stored in the cache. The <directive>CacheStorePrivate</directive>
383 directive allows this behavior to be overridden.
384 <directive>CacheStorePrivate</directive> On
385 tells the server to attempt to cache the resource even if it contains
386 private header values. Resources requiring authorization will
387 <em>never</em> be cached.</p>
393 <note type="warning"><title>Warning:</title>
394 This directive will allow caching even if the upstream server has
395 requested that the resource not be cached. This directive is only
396 ideal for a 'private' cache.
399 <seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>
400 <seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>
404 <name>CacheStoreNoStore</name>
405 <description>Attempt to cache requests or responses that have been marked as no-store.</description>
406 <syntax>CacheStoreNoStore On|Off</syntax>
407 <default>CacheStoreNoStore Off</default>
408 <contextlist><context>server config</context><context>virtual host</context>
412 <p>Ordinarily, requests or responses with Cache-Control: no-store header
413 values will not be stored in the cache. The
414 <directive>CacheStoreNoCache</directive> directive allows this
415 behavior to be overridden. <directive>CacheStoreNoCache</directive> On
416 tells the server to attempt to cache the resource even if it contains
417 no-store header values. Resources requiring authorization will
418 <em>never</em> be cached.</p>
424 <note type="warning"><title>Warning:</title>
425 As described in RFC 2616, the no-store directive is intended to
426 "prevent the inadvertent release or retention of sensitive information
427 (for example, on backup tapes)." Enabling this option could store
428 sensitive information in the cache. You are hereby warned.
431 <seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>
432 <seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>