2 <!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
3 <?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
4 <!-- $Revision: 1.17 $ -->
7 Copyright 2002-2004 The Apache Software Foundation
9 Licensed under the Apache License, Version 2.0 (the "License");
10 you may not use this file except in compliance with the License.
11 You may obtain a copy of the License at
13 http://www.apache.org/licenses/LICENSE-2.0
15 Unless required by applicable law or agreed to in writing, software
16 distributed under the License is distributed on an "AS IS" BASIS,
17 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
18 See the License for the specific language governing permissions and
19 limitations under the License.
22 <modulesynopsis metafile="mod_cache.xml.meta">
24 <name>mod_cache</name>
25 <description>Content cache keyed to URIs.</description>
26 <status>Experimental</status>
27 <sourcefile>mod_cache.c</sourcefile>
28 <identifier>cache_module</identifier>
32 This module is experimental. Documentation is still under development...
35 <p><module>mod_cache</module> implements an <a
36 href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a> compliant HTTP
37 content cache that can be used to cache either local or proxied content.
38 <module>mod_cache</module> requires the services of one or more storage
39 management modules. Two storage management modules are included in
40 the base Apache distribution:</p>
42 <dt><module>mod_disk_cache</module></dt>
43 <dd>implements a disk based storage manager.</dd>
45 <dt><module>mod_mem_cache</module></dt>
46 <dd>implements a memory based storage manager.
47 <module>mod_mem_cache</module> can be configured to operate in two
48 modes: caching open file descriptors or caching objects in heap storage.
49 <module>mod_mem_cache</module> can be used to cache locally generated content
50 or to cache backend server content for <module>mod_proxy</module> when
51 configured using <directive module="mod_proxy">ProxyPass</directive>
52 (aka <dfn>reverse proxy</dfn>)</dd>
55 <p>Content is stored in and retrieved from the cache using URI based keys. Content with
56 access protection is not cached.</p>
59 <section id="related"><title>Related Modules and Directives</title>
62 <module>mod_disk_cache</module>
63 <module>mod_mem_cache</module>
66 <directive module="mod_disk_cache">CacheRoot</directive>
67 <directive module="mod_disk_cache">CacheSize</directive>
68 <directive module="mod_disk_cache">CacheGcInterval</directive>
69 <directive module="mod_disk_cache">CacheDirLevels</directive>
70 <directive module="mod_disk_cache">CacheDirLength</directive>
71 <directive module="mod_disk_cache">CacheExpiryCheck</directive>
72 <directive module="mod_disk_cache">CacheMinFileSize</directive>
73 <directive module="mod_disk_cache">CacheMaxFileSize</directive>
74 <directive module="mod_disk_cache">CacheTimeMargin</directive>
75 <directive module="mod_disk_cache">CacheGcDaily</directive>
76 <directive module="mod_disk_cache">CacheGcUnused</directive>
77 <directive module="mod_disk_cache">CacheGcClean</directive>
78 <directive module="mod_disk_cache">CacheGcMemUsage</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 <IfModule mod_disk_cache.c><br />
101 CacheRoot c:/cacheroot<br />
103 CacheEnable disk /<br />
104 CacheDirLevels 5<br />
105 CacheDirLength 3<br />
107 </IfModule> <br />
109 LoadModule mem_cache_module modules/mod_mem_cache.so<br />
110 <IfModule mod_mem_cache.c><br />
112 CacheEnable mem /<br />
113 MCacheSize 4096<br />
114 MCacheMaxObjectCount 100<br />
115 MCacheMinObjectSize 1<br />
116 MCacheMaxObjectSize 2048<br />
118 </IfModule><br />
125 <name>CacheEnable</name>
126 <description>Enable caching of specified URLs using a specified storage
127 manager</description>
128 <syntax>CacheEnable <var>cache_type</var> <var>url-string</var></syntax>
129 <contextlist><context>server config</context><context>virtual host</context>
133 <p>The <directive>CacheEnable</directive> directive instructs
134 <module>mod_cache</module> to cache urls at or below
135 <var>url-string</var>. The cache storage manager is specified with the
136 <var>cache_type</var> argument. <var>cache_type</var> <code> mem</code>
137 instructs <module>mod_cache</module> to use the memory based storage
138 manager implemented by <module>mod_mem_cache</module>.
139 <var>cache_type</var> <code>disk</code> instructs
140 <module>mod_cache</module> to use the disk based storage manager
141 implemented by <module>mod_disk_cache</module>.
142 <var>cache_type</var> <code>fd</code> instructs
143 <module>mod_cache</module> to use the file descriptor cache implemented
144 by <module>mod_mem_cache</module>.</p>
145 <p>In the event that the URL space overlaps between different
146 <directive>CacheEnable</directive> directives (as in the example below),
147 each possible storage manager will be run until the first one that
148 actually processes the request. The order in which the storage managers are
149 run is determined by the order of the <directive>CacheEnable</directive>
150 directives in the configuration file.</p>
153 CacheEnable mem /manual<br />
154 CacheEnable fd /images<br />
155 CacheEnable disk /<br />
161 <name>CacheDisable</name>
162 <description>Disable caching of specified URLs</description>
163 <syntax>CacheDisable <var> url-string</var></syntax>
164 <contextlist><context>server config</context><context>virtual host</context>
168 <p>The <directive>CacheDisable</directive> directive instructs
169 <module>mod_cache</module> to <em>not</em> cache urls at or below
170 <var>url-string</var>.</p>
172 <example><title>Example</title>
173 CacheDisable /local_files
179 <name>CacheMaxExpire</name>
180 <description>The maximum time in seconds to cache a document</description>
181 <syntax>CacheMaxExpire <var>seconds</var></syntax>
182 <default>CacheMaxExpire 86400 (one day)</default>
183 <contextlist><context>server config</context><context>virtual host</context>
187 <p>The <directive>CacheMaxExpire</directive> directive specifies the maximum number of
188 seconds for which cachable HTTP documents will be retained without checking the origin
189 server. Thus, documents will be out of date at most this number of seconds. This maximum
190 value is enforced even if an expiry date was supplied with the document.</p>
193 CacheMaxExpire 604800
199 <name>CacheDefaultExpire</name>
200 <description>The default duration to cache a document when no expiry date is specified.</description>
201 <syntax>CacheDefaultExpire <var>seconds</var></syntax>
202 <default>CacheDefaultExpire 3600 (one hour)</default>
203 <contextlist><context>server config</context><context>virtual host</context>
207 <p>The <directive>CacheDefaultExpire</directive> directive specifies a default time,
208 in seconds, to cache a document if neither an expiry date nor last-modified date are provided
209 with the document. The value specified with the <directive>CacheMaxExpire</directive>
210 directive does <em>not</em> override this setting.</p>
213 CacheDefaultExpire 86400
219 <name>CacheIgnoreNoLastMod</name>
220 <description>Ignore the fact that a response has no Last Modified
221 header.</description>
222 <syntax>CacheIgnoreNoLastMod On|Off</syntax>
223 <default>CacheIgnoreNoLastMod Off</default>
224 <contextlist><context>server config</context><context>virtual host</context>
228 <p>Ordinarily, documents without a last-modified date are not cached.
229 Under some circumstances the last-modified date is removed (during
230 <module>mod_include</module> processing for example) or not provided
231 at all. The <directive>CacheIgnoreNoLastMod</directive> directive
232 provides a way to specify that documents without last-modified dates
233 should be considered for caching, even without a last-modified date.
234 If neither a last-modified date nor an expiry date are provided with
235 the document then the value specified by the
236 <directive>CacheDefaultExpire</directive> directive will be used to
237 generate an expiration date.</p>
240 CacheIgnoreNoLastMod On
246 <name>CacheIgnoreCacheControl</name>
247 <description>Ignore the fact that the client requested the content not be
248 cached.</description>
249 <syntax>CacheIgnoreCacheControl On|Off</syntax>
250 <default>CacheIgnoreCacheControl Off</default>
251 <contextlist><context>server config</context><context>virtual host</context>
255 <p>Ordinarily, documents with no-cache or no-store header values will not be stored in the cache.
256 The <directive>CacheIgnoreCacheControl</directive> directive allows this behavior to be overridden.
257 <directive>CacheIgnoreCacheControl</directive> On tells the server to attempt to cache the document
258 even if it contains no-cache or no-store header values. Documents requiring authorization will
259 <em>never</em> be cached.</p>
262 CacheIgnoreCacheControl On
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>CacheForceCompletion</name>
304 <description>Percentage of document served, after which the server
305 will complete caching the file even if the request is cancelled.</description>
306 <syntax>CacheForceCompletion <var>Percentage</var></syntax>
307 <default>CacheForceCompletion 60</default>
308 <contextlist><context>server config</context><context>virtual host</context>
312 <p>Ordinarily, if a request is cancelled while the response is being
313 cached and delivered to the client the processing of the response will
314 stop and the cache entry will be removed. The
315 <directive>CacheForceCompletion</directive> directive specifies a
316 threshold beyond which the document will continue to be cached to
317 completion, even if the request is cancelled.</p>
319 <p>The threshold is a percentage specified as a value between
320 <code>1</code> and <code>100</code>. A value of <code>0</code>
321 specifies that the default be used. A value of <code>100</code>
322 will only cache documents that are served in their entirety. A value
323 between 60 and 90 is recommended.</p>
326 CacheForceCompletion 80
329 <note type="warning"><title>Note:</title>
330 This feature is currently <em>not</em> implemented.