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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,
90 # uncomment the line above and comment out the LoadModule line below.
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 />
116 <name>CacheEnable</name>
117 <description>Enable caching of specified URLs using a specified storage
118 manager</description>
119 <syntax>CacheEnable <var>cache_type</var> <var>url-string</var></syntax>
120 <contextlist><context>server config</context><context>virtual host</context>
124 <p>The <directive>CacheEnable</directive> directive instructs
125 <module>mod_cache</module> to cache urls at or below
126 <var>url-string</var>. The cache storage manager is specified with the
127 <var>cache_type</var> argument. <var>cache_type</var> <code> mem</code>
128 instructs <module>mod_cache</module> to use the memory based storage
129 manager implemented by <module>mod_mem_cache</module>.
130 <var>cache_type</var> <code>disk</code> instructs
131 <module>mod_cache</module> to use the disk based storage manager
132 implemented by <module>mod_disk_cache</module>.
133 <var>cache_type</var> <code>fd</code> instructs
134 <module>mod_cache</module> to use the file descriptor cache implemented
135 by <module>mod_mem_cache</module>.</p>
136 <p>In the event that the URL space overlaps between different
137 <directive>CacheEnable</directive> directives (as in the example below),
138 each possible storage manager will be run until the first one that
139 actually processes the request. The order in which the storage managers are
140 run is determined by the order of the <directive>CacheEnable</directive>
141 directives in the configuration file.</p>
144 CacheEnable mem /manual<br />
145 CacheEnable fd /images<br />
146 CacheEnable disk /<br />
152 <name>CacheDisable</name>
153 <description>Disable caching of specified URLs</description>
154 <syntax>CacheDisable <var> url-string</var></syntax>
155 <contextlist><context>server config</context><context>virtual host</context>
159 <p>The <directive>CacheDisable</directive> directive instructs
160 <module>mod_cache</module> to <em>not</em> cache urls at or below
161 <var>url-string</var>.</p>
163 <example><title>Example</title>
164 CacheDisable /local_files
170 <name>CacheMaxExpire</name>
171 <description>The maximum time in seconds to cache a document</description>
172 <syntax>CacheMaxExpire <var>seconds</var></syntax>
173 <default>CacheMaxExpire 86400 (one day)</default>
174 <contextlist><context>server config</context><context>virtual host</context>
178 <p>The <directive>CacheMaxExpire</directive> directive specifies the maximum number of
179 seconds for which cachable HTTP documents will be retained without checking the origin
180 server. Thus, documents will be out of date at most this number of seconds. This maximum
181 value is enforced even if an expiry date was supplied with the document.</p>
184 CacheMaxExpire 604800
190 <name>CacheDefaultExpire</name>
191 <description>The default duration to cache a document when no expiry date is specified.</description>
192 <syntax>CacheDefaultExpire <var>seconds</var></syntax>
193 <default>CacheDefaultExpire 3600 (one hour)</default>
194 <contextlist><context>server config</context><context>virtual host</context>
198 <p>The <directive>CacheDefaultExpire</directive> directive specifies a default time,
199 in seconds, to cache a document if neither an expiry date nor last-modified date are provided
200 with the document. The value specified with the <directive>CacheMaxExpire</directive>
201 directive does <em>not</em> override this setting.</p>
204 CacheDefaultExpire 86400
210 <name>CacheIgnoreNoLastMod</name>
211 <description>Ignore the fact that a response has no Last Modified
212 header.</description>
213 <syntax>CacheIgnoreNoLastMod On|Off</syntax>
214 <default>CacheIgnoreNoLastMod Off</default>
215 <contextlist><context>server config</context><context>virtual host</context>
219 <p>Ordinarily, documents without a last-modified date are not cached.
220 Under some circumstances the last-modified date is removed (during
221 <module>mod_include</module> processing for example) or not provided
222 at all. The <directive>CacheIgnoreNoLastMod</directive> directive
223 provides a way to specify that documents without last-modified dates
224 should be considered for caching, even without a last-modified date.
225 If neither a last-modified date nor an expiry date are provided with
226 the document then the value specified by the
227 <directive>CacheDefaultExpire</directive> directive will be used to
228 generate an expiration date.</p>
231 CacheIgnoreNoLastMod On
237 <name>CacheIgnoreCacheControl</name>
238 <description>Ignore request to not serve cached content to client</description>
239 <syntax>CacheIgnoreCacheControl On|Off</syntax>
240 <default>CacheIgnoreCacheControl Off</default>
241 <contextlist><context>server config</context><context>virtual host</context>
245 <p>Ordinarily, requests containing a Cache-Control: no-cache or
246 Pragma: no-cache header value will not be served from the cache. The
247 <directive>CacheIgnoreCacheControl</directive> directive allows this
248 behavior to be overridden. <directive>CacheIgnoreCacheControl</directive>
249 On tells the server to attempt to serve the resource from the cache even
250 if the request contains no-cache header values. Resources requiring
251 authorization will <em>never</em> be cached.</p>
254 CacheIgnoreCacheControl On
257 <note type="warning"><title>Warning:</title>
258 This directive will allow serving from the cache even if the client has
259 requested that the document not be served from the cache. This might
260 result in stale content being served.
263 <seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>
264 <seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>
268 <name>CacheLastModifiedFactor</name>
269 <description>The factor used to compute an expiry date based on the
270 LastModified date.</description>
271 <syntax>CacheLastModifiedFactor <var>float</var></syntax>
272 <default>CacheLastModifiedFactor 0.1</default>
273 <contextlist><context>server config</context><context>virtual host</context>
277 <p>In the event that a document does not provide an expiry date but does
278 provide a last-modified date, an expiry date can be calculated based on
279 the time since the document was last modified. The
280 <directive>CacheLastModifiedFactor</directive> directive specifies a
281 <var>factor</var> to be used in the generation of this expiry date
282 according to the following formula:
284 <code>expiry-period = time-since-last-modified-date * <var>factor</var>
285 expiry-date = current-date + expiry-period</code>
287 For example, if the document was last modified 10 hours ago, and
288 <var>factor</var> is 0.1 then the expiry-period will be set to
289 10*0.1 = 1 hour. If the current time was 3:00pm then the computed
290 expiry-date would be 3:00pm + 1hour = 4:00pm.
292 If the expiry-period would be longer than that set by
293 <directive>CacheMaxExpire</directive>, then the latter takes
297 CacheLastModifiedFactor 0.5
303 <name>CacheIgnoreHeaders</name>
304 <description>Do not store the given HTTP header(s) in the cache.
306 <syntax>CacheIgnoreHeaders <var>header-string</var> [<var>header-string</var>] ...</syntax>
307 <default>CacheIgnoreHeaders None</default>
308 <contextlist><context>server config</context><context>virtual host</context>
312 <p>According to RFC 2616, hop-by-hop HTTP headers are not stored in
313 the cache. The following HTTP headers are hop-by-hop headers and thus
314 do not get stored in the cache in <em>any</em> case regardless of the
315 setting of <directive>CacheIgnoreHeaders</directive>:</p>
318 <li><code>Connection</code></li>
319 <li><code>Keep-Alive</code></li>
320 <li><code>Proxy-Authenticate</code></li>
321 <li><code>Proxy-Authorization</code></li>
322 <li><code>TE</code></li>
323 <li><code>Trailers</code></li>
324 <li><code>Transfer-Encoding</code></li>
325 <li><code>Upgrade</code></li>
328 <p><directive>CacheIgnoreHeaders</directive> specifies additional HTTP
329 headers that should not to be stored in the cache. For example, it makes
330 sense in some cases to prevent cookies from being stored in the cache.</p>
332 <p><directive>CacheIgnoreHeaders</directive> takes a space separated list
333 of HTTP headers that should not be stored in the cache. If only hop-by-hop
334 headers not should be stored in the cache (the RFC 2616 compliant
335 behaviour), <directive>CacheIgnoreHeaders</directive> can be set to
336 <code>None</code>.</p>
338 <example><title>Example 1</title>
339 CacheIgnoreHeaders Set-Cookie
342 <example><title>Example 2</title>
343 CacheIgnoreHeaders None
346 <note type="warning"><title>Warning:</title>
347 If headers like <code>Expires</code> which are needed for proper cache
348 management are not stored due to a
349 <directive>CacheIgnoreHeaders</directive> setting, the behaviour of
350 mod_cache is undefined.
356 <name>CacheStorePrivate</name>
357 <description>Attempt to cache responses that the server has marked as private</description>
358 <syntax>CacheStorePrivate On|Off</syntax>
359 <default>CacheStorePrivate Off</default>
360 <contextlist><context>server config</context><context>virtual host</context>
364 <p>Ordinarily, responses with Cache-Control: private header values will not
365 be stored in the cache. The <directive>CacheStorePrivate</directive>
366 directive allows this behavior to be overridden.
367 <directive>CacheStorePrivate</directive> On
368 tells the server to attempt to cache the resource even if it contains
369 private header values. Resources requiring authorization will
370 <em>never</em> be cached.</p>
376 <note type="warning"><title>Warning:</title>
377 This directive will allow caching even if the upstream server has
378 requested that the resource not be cached. This directive is only
379 ideal for a 'private' cache.
382 <seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>
383 <seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>
387 <name>CacheStoreNoStore</name>
388 <description>Attempt to cache requests or responses that have been marked as no-store.</description>
389 <syntax>CacheStoreNoStore On|Off</syntax>
390 <default>CacheStoreNoStore Off</default>
391 <contextlist><context>server config</context><context>virtual host</context>
395 <p>Ordinarily, requests or responses with Cache-Control: no-store header
396 values will not be stored in the cache. The
397 <directive>CacheStoreNoCache</directive> directive allows this
398 behavior to be overridden. <directive>CacheStoreNoCache</directive> On
399 tells the server to attempt to cache the resource even if it contains
400 no-store header values. Resources requiring authorization will
401 <em>never</em> be cached.</p>
407 <note type="warning"><title>Warning:</title>
408 As described in RFC 2616, the no-store directive is intended to
409 "prevent the inadvertent release or retention of sensitive information
410 (for example, on backup tapes)." Enabling this option could store
411 sensitive information in the cache. You are hereby warned.
414 <seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>
415 <seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>