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19 <p class="apache">Apache HTTP Server Version 2.5</p>
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24 <div id="page-content">
25 <div id="preamble"><h1>Apache Module mod_cache</h1>
27 <p><span>Available Languages: </span><a href="../en/mod/mod_cache.html" title="English"> en </a> |
28 <a href="../fr/mod/mod_cache.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
29 <a href="../ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
30 <a href="../ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
32 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>RFC 2616 compliant HTTP caching filter.</td></tr>
33 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
34 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>cache_module</td></tr>
35 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_cache.c</td></tr></table>
38 <div class="warning">This module should be used with care, as when the
39 <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code> directive is
40 in its default value of <strong>on</strong>, the <code class="directive"><a href="../mod/mod_access_compat.html#allow">Allow</a></code> and <code class="directive"><a href="../mod/mod_access_compat.html#deny">Deny</a></code> directives will be circumvented.
41 You should not enable quick handler caching for any content to which you
42 wish to limit access by client host name, address or environment
45 <p><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> implements an <a href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a> compliant
46 <strong>HTTP content caching filter</strong>, with support for the caching
47 of content negotiated responses containing the Vary header.</p>
49 <p>RFC 2616 compliant caching provides a mechanism to verify whether
50 stale or expired content is still fresh, and can represent a significant
51 performance boost when the origin server supports <strong>conditional
52 requests</strong> by honouring the
53 <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26">If-None-Match</a>
54 HTTP request header. Content is only regenerated from scratch when the content
55 has changed, and not when the cached entry expires.</p>
57 <p>As a filter, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> can be placed in front of
58 content originating from any handler, including <strong>flat
59 files</strong> (served from a slow disk cached on a fast disk), the output
60 of a <strong>CGI script</strong> or <strong>dynamic content
61 generator</strong>, or content <strong>proxied from another
64 <p>In the default configuration, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> inserts the
65 caching filter as far forward as possible within the filter stack,
66 utilising the <strong>quick handler</strong> to bypass all per request
67 processing when returning content to the client. In this mode of
68 operation, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> may be thought of as a caching
69 proxy server bolted to the front of the webserver, while running within
70 the webserver itself.</p>
72 <p>When the quick handler is switched off using the
73 <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code> directive,
74 it becomes possible to insert the <strong>CACHE</strong> filter at a
75 point in the filter stack chosen by the administrator. This provides the
76 opportunity to cache content before that content is personalised by the
77 <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> filter, or optionally compressed by the
78 <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> filter.</p>
80 <p>Under normal operation, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> will respond to
81 and can be controlled by the
82 <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9">Cache-Control</a>
84 <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.32">Pragma</a>
85 headers sent from a client in a request, or from a
86 server within a response. Under exceptional circumstances,
87 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> can be configured to override these headers
88 and force site specific behaviour, however such behaviour will be limited
89 to this cache only, and will not affect the operation of other caches
90 that may exist between the client and server, and as a result is not
91 recommended unless strictly necessary.</p>
93 <p>RFC 2616 allows for the cache to return stale data while the existing
94 stale entry is refreshed from the origin server, and this is supported
95 by <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> when the
96 <code class="directive"><a href="#cachelock">CacheLock</a></code> directive is suitably
97 configured. Such responses will contain a
98 <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.46">Warning</a>
99 HTTP header with a 110 response code. RFC 2616 also allows a cache to return
100 stale data when the attempt made to refresh the stale data returns an
101 error 500 or above, and this behaviour is supported by default by
102 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>. Such responses will contain a
103 <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.46">Warning</a>
104 HTTP header with a 111 response code.</p>
106 <p><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> requires the services of one or more
107 storage management modules. The following storage management modules are included in
108 the base Apache distribution:</p>
110 <dt><code class="module"><a href="../mod/mod_cache_disk.html">mod_cache_disk</a></code></dt>
111 <dd>Implements a disk based storage manager. Headers and bodies are
112 stored separately on disk, in a directory structure derived from the
113 md5 hash of the cached URL. Multiple content negotiated responses can
114 be stored concurrently, however the caching of partial content is not
115 supported by this module. The <code class="program"><a href="../programs/htcacheclean.html">htcacheclean</a></code> tool is
116 provided to list cached URLs, remove cached URLs, or to maintain the size
117 of the disk cache within size and inode limits.</dd>
118 <dt><code class="module"><a href="../mod/mod_cache_socache.html">mod_cache_socache</a></code></dt>
119 <dd>Implements a shared object cache based storage manager. Headers and
120 bodies are stored together beneath a single key based on the URL of the
121 response being cached. Multiple content negotiated responses can
122 be stored concurrently, however the caching of partial content is not
123 supported by this module.</dd>
126 <p>Further details, discussion, and examples, are provided in the
127 <a href="../caching.html">Caching Guide</a>.</p>
129 <div id="quickview"><h3 class="directives">Directives</h3>
131 <li><img alt="" src="../images/down.gif" /> <a href="#cachedefaultexpire">CacheDefaultExpire</a></li>
132 <li><img alt="" src="../images/down.gif" /> <a href="#cachedetailheader">CacheDetailHeader</a></li>
133 <li><img alt="" src="../images/down.gif" /> <a href="#cachedisable">CacheDisable</a></li>
134 <li><img alt="" src="../images/down.gif" /> <a href="#cacheenable">CacheEnable</a></li>
135 <li><img alt="" src="../images/down.gif" /> <a href="#cacheheader">CacheHeader</a></li>
136 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></li>
137 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignoreheaders">CacheIgnoreHeaders</a></li>
138 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignorenolastmod">CacheIgnoreNoLastMod</a></li>
139 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignorequerystring">CacheIgnoreQueryString</a></li>
140 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignoreurlsessionidentifiers">CacheIgnoreURLSessionIdentifiers</a></li>
141 <li><img alt="" src="../images/down.gif" /> <a href="#cachekeybaseurl">CacheKeyBaseURL</a></li>
142 <li><img alt="" src="../images/down.gif" /> <a href="#cachelastmodifiedfactor">CacheLastModifiedFactor</a></li>
143 <li><img alt="" src="../images/down.gif" /> <a href="#cachelock">CacheLock</a></li>
144 <li><img alt="" src="../images/down.gif" /> <a href="#cachelockmaxage">CacheLockMaxAge</a></li>
145 <li><img alt="" src="../images/down.gif" /> <a href="#cachelockpath">CacheLockPath</a></li>
146 <li><img alt="" src="../images/down.gif" /> <a href="#cachemaxexpire">CacheMaxExpire</a></li>
147 <li><img alt="" src="../images/down.gif" /> <a href="#cacheminexpire">CacheMinExpire</a></li>
148 <li><img alt="" src="../images/down.gif" /> <a href="#cachequickhandler">CacheQuickHandler</a></li>
149 <li><img alt="" src="../images/down.gif" /> <a href="#cachestaleonerror">CacheStaleOnError</a></li>
150 <li><img alt="" src="../images/down.gif" /> <a href="#cachestoreexpired">CacheStoreExpired</a></li>
151 <li><img alt="" src="../images/down.gif" /> <a href="#cachestorenostore">CacheStoreNoStore</a></li>
152 <li><img alt="" src="../images/down.gif" /> <a href="#cachestoreprivate">CacheStorePrivate</a></li>
156 <li><img alt="" src="../images/down.gif" /> <a href="#related">Related Modules and Directives</a></li>
157 <li><img alt="" src="../images/down.gif" /> <a href="#sampleconf">Sample Configuration</a></li>
158 <li><img alt="" src="../images/down.gif" /> <a href="#thunderingherd">Avoiding the Thundering Herd</a></li>
159 <li><img alt="" src="../images/down.gif" /> <a href="#finecontrol">Fine Control with the CACHE Filter</a></li>
160 <li><img alt="" src="../images/down.gif" /> <a href="#status">Cache Status and Logging</a></li>
161 </ul><h3>See also</h3>
163 <li><a href="../caching.html">Caching Guide</a></li>
164 </ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
165 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
166 <div class="section">
167 <h2><a name="related" id="related">Related Modules and Directives</a></h2>
168 <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="../mod/mod_cache_disk.html">mod_cache_disk</a></code></li><li><code class="module"><a href="../mod/mod_cache_socache.html">mod_cache_socache</a></code></li></ul></td><td><ul><li><code class="directive"><a href="../mod/mod_cache_disk.html#cacheroot">CacheRoot</a></code></li><li><code class="directive"><a href="../mod/mod_cache_disk.html#cachedirlevels">CacheDirLevels</a></code></li><li><code class="directive"><a href="../mod/mod_cache_disk.html#cachedirlength">CacheDirLength</a></code></li><li><code class="directive"><a href="../mod/mod_cache_disk.html#cacheminfilesize">CacheMinFileSize</a></code></li><li><code class="directive"><a href="../mod/mod_cache_disk.html#cachemaxfilesize">CacheMaxFileSize</a></code></li><li><code class="directive"><a href="../mod/mod_cache_socache.html#cachesocache">CacheSocache</a></code></li><li><code class="directive"><a href="../mod/mod_cache_socache.html#cachesocachemaxtime">CacheSocacheMaxTime</a></code></li><li><code class="directive"><a href="../mod/mod_cache_socache.html#cachesocachemintime">CacheSocacheMinTime</a></code></li><li><code class="directive"><a href="../mod/mod_cache_socache.html#cachesocachemaxsize">CacheSocacheMaxSize</a></code></li><li><code class="directive"><a href="../mod/mod_cache_socache.html#cachesocachereadsize">CacheSocacheReadSize</a></code></li><li><code class="directive"><a href="../mod/mod_cache_socache.html#cachesocachereadtime">CacheSocacheReadTime</a></code></li></ul></td></tr></table>
169 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
170 <div class="section">
171 <h2><a name="sampleconf" id="sampleconf">Sample Configuration</a></h2>
172 <div class="example"><h3>Sample httpd.conf</h3><pre class="prettyprint lang-config">#
173 # Sample Cache Configuration
175 LoadModule cache_module modules/mod_cache.so
176 <IfModule mod_cache.c>
177 LoadModule cache_disk_module modules/mod_cache_disk.so
178 <IfModule mod_cache_disk.c>
179 CacheRoot c:/cacheroot
185 # When acting as a proxy, don't cache the list of security updates
186 CacheDisable http://security.update.server/update-list/
187 </IfModule></pre>
189 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
190 <div class="section">
191 <h2><a name="thunderingherd" id="thunderingherd">Avoiding the Thundering Herd</a></h2>
192 <p>When a cached entry becomes stale, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> will submit
193 a conditional request to the backend, which is expected to confirm whether the
194 cached entry is still fresh, and send an updated entity if not.</p>
195 <p>A small but finite amount of time exists between the time the cached entity
196 becomes stale, and the time the stale entity is fully refreshed. On a busy
197 server, a significant number of requests might arrive during this time, and
198 cause a <strong>thundering herd</strong> of requests to strike the backend
199 suddenly and unpredictably.</p>
200 <p>To keep the thundering herd at bay, the <code class="directive">CacheLock</code>
201 directive can be used to define a directory in which locks are created for
202 URLs <strong>in flight</strong>. The lock is used as a <strong>hint</strong>
203 by other requests to either suppress an attempt to cache (someone else has
204 gone to fetch the entity), or to indicate that a stale entry is being refreshed
205 (stale content will be returned in the mean time).
207 <h3>Initial caching of an entry</h3>
209 <p>When an entity is cached for the first time, a lock will be created for the
210 entity until the response has been fully cached. During the lifetime of the
211 lock, the cache will suppress the second and subsequent attempt to cache the
212 same entity. While this doesn't hold back the thundering herd, it does stop
213 the cache attempting to cache the same entity multiple times simultaneously.
216 <h3>Refreshment of a stale entry</h3>
218 <p>When an entity reaches its freshness lifetime and becomes stale, a lock
219 will be created for the entity until the response has either been confirmed as
220 still fresh, or replaced by the backend. During the lifetime of the lock, the
221 second and subsequent incoming request will cause stale data to be returned,
222 and the thundering herd is kept at bay.</p>
224 <h3>Locks and Cache-Control: no-cache</h3>
226 <p>Locks are used as a <strong>hint only</strong> to enable the cache to be
227 more gentle on backend servers, however the lock can be overridden if necessary.
228 If the client sends a request with a Cache-Control header forcing a reload, any
229 lock that may be present will be ignored, and the client's request will be
230 honored immediately and the cached entry refreshed.</p>
231 <p>As a further safety mechanism, locks have a configurable maximum age.
232 Once this age has been reached, the lock is removed, and a new request is
233 given the opportunity to create a new lock. This maximum age can be set using
234 the <code class="directive">CacheLockMaxAge</code> directive, and defaults to 5
238 <h3>Example configuration</h3>
240 <div class="example"><h3>Enabling the cache lock</h3><pre class="prettyprint lang-config">#
241 # Enable the cache lock
243 <IfModule mod_cache.c>
245 CacheLockPath /tmp/mod_cache-lock
247 </IfModule></pre>
250 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
251 <div class="section">
252 <h2><a name="finecontrol" id="finecontrol">Fine Control with the CACHE Filter</a></h2>
253 <p>Under the default mode of cache operation, the cache runs as a quick handler,
254 short circuiting the majority of server processing and offering the highest
255 cache performance available.</p>
257 <p>In this mode, the cache <strong>bolts onto</strong> the front of the server,
258 acting as if a free standing RFC 2616 caching proxy had been placed in front of
261 <p>While this mode offers the best performance, the administrator may find that
262 under certain circumstances they may want to perform further processing on the
263 request after the request is cached, such as to inject personalisation into the
264 cached page, or to apply authorization restrictions to the content. Under these
265 circumstances, an administrator is often forced to place independent reverse
266 proxy servers either behind or in front of the caching server to achieve this.</p>
268 <p>To solve this problem the <code class="directive"><a href="#cachequickhandler">CacheQuickHandler
269 </a></code> directive can be set to <strong>off</strong>, and the server will
270 process all phases normally handled by a non-cached request, including the
271 <strong>authentication and authorization</strong> phases.</p>
273 <p>In addition, the administrator may optionally specify the <strong>precise point
274 within the filter chain</strong> where caching is to take place by adding the
275 <strong>CACHE</strong> filter to the output filter chain.</p>
277 <p>For example, to cache content before applying compression to the response,
278 place the <strong>CACHE</strong> filter before the <strong>DEFLATE</strong>
279 filter as in the example below:</p>
281 <pre class="prettyprint lang-config"># Cache content before optional compression
282 CacheQuickHandler off
283 AddOutputFilterByType CACHE;DEFLATE text/plain</pre>
286 <p>Another option is to have content cached before personalisation is applied
287 by <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> (or another content processing filter). In this
288 example templates containing tags understood by
289 <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> are cached before being parsed:</p>
291 <pre class="prettyprint lang-config"># Cache content before mod_include and mod_deflate
292 CacheQuickHandler off
293 AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html</pre>
296 <p>You may place the <strong>CACHE</strong> filter anywhere you wish within the
297 filter chain. In this example, content is cached after being parsed by
298 <code class="module"><a href="../mod/mod_include.html">mod_include</a></code>, but before being processed by
299 <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code>:</p>
301 <pre class="prettyprint lang-config"># Cache content between mod_include and mod_deflate
302 CacheQuickHandler off
303 AddOutputFilterByType INCLUDES;CACHE;DEFLATE text/html</pre>
306 <div class="warning"><h3>Warning:</h3>If the location of the
307 <strong>CACHE</strong> filter in the filter chain is changed for any reason,
308 you may need to <strong>flush your cache</strong> to ensure that your data
309 served remains consistent. <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> is not in a position
310 to enforce this for you.</div>
312 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
313 <div class="section">
314 <h2><a name="status" id="status">Cache Status and Logging</a></h2>
315 <p>Once <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> has made a decision as to whether or not
316 an entity is to be served from cache, the detailed reason for the decision
317 is written to the subprocess environment within the request under the
318 <strong>cache-status</strong> key. This reason can be logged by the
319 <code class="directive"><a href="../mod/mod_log_config.html#logformat">LogFormat</a></code> directive as
322 <pre class="prettyprint lang-config">LogFormat "%{cache-status}e ..."</pre>
325 <p>Based on the caching decision made, the reason is also written to the
326 subprocess environment under one the following four keys, as appropriate:</p>
329 <dt>cache-hit</dt><dd>The response was served from cache.</dd>
330 <dt>cache-revalidate</dt><dd>The response was stale and was successfully
331 revalidated, then served from cache.</dd>
332 <dt>cache-miss</dt><dd>The response was served from the upstream server.</dd>
333 <dt>cache-invalidate</dt><dd>The cached entity was invalidated by a request
334 method other than GET or HEAD.</dd>
337 <p>This makes it possible to support conditional logging of cached requests
338 as per the following example:</p>
340 <pre class="prettyprint lang-config">CustomLog cached-requests.log common env=cache-hit
341 CustomLog uncached-requests.log common env=cache-miss
342 CustomLog revalidated-requests.log common env=cache-revalidate
343 CustomLog invalidated-requests.log common env=cache-invalidate</pre>
346 <p>For module authors, a hook called <var>cache_status</var> is available,
347 allowing modules to respond to the caching outcomes above in customised
350 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
351 <div class="directive-section"><h2><a name="CacheDefaultExpire" id="CacheDefaultExpire">CacheDefaultExpire</a> <a name="cachedefaultexpire" id="cachedefaultexpire">Directive</a></h2>
352 <table class="directive">
353 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The default duration to cache a document when no expiry date is specified.</td></tr>
354 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDefaultExpire <var>seconds</var></code></td></tr>
355 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheDefaultExpire 3600 (one hour)</code></td></tr>
356 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
357 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
358 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
360 <p>The <code class="directive">CacheDefaultExpire</code> directive specifies a default time,
361 in seconds, to cache a document if neither an expiry date nor last-modified date are provided
362 with the document. The value specified with the <code class="directive">CacheMaxExpire</code>
363 directive does <em>not</em> override this setting.</p>
365 <pre class="prettyprint lang-config">CacheDefaultExpire 86400</pre>
369 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
370 <div class="directive-section"><h2><a name="CacheDetailHeader" id="CacheDetailHeader">CacheDetailHeader</a> <a name="cachedetailheader" id="cachedetailheader">Directive</a></h2>
371 <table class="directive">
372 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Add an X-Cache-Detail header to the response.</td></tr>
373 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDetailHeader <var>on|off</var></code></td></tr>
374 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheDetailHeader off</code></td></tr>
375 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
376 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
377 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
378 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr>
380 <p>When the <code class="directive"><a href="#cachedetailheader">CacheDetailHeader</a></code> directive
381 is switched on, an <strong>X-Cache-Detail</strong> header will be added to the response
382 containing the detailed reason for a particular caching decision.</p>
384 <p>It can be useful during development of cached RESTful services to have additional
385 information about the caching decision written to the response headers, so as to
386 confirm whether <code>Cache-Control</code> and other headers have been correctly
387 used by the service and client.</p>
389 <p>If the normal handler is used, this directive may appear within a
390 <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code> or
391 <code class="directive"><a href="../mod/core.html#location"><Location></a></code> directive. If the quick handler
392 is used, this directive must appear within a server or virtual host context, otherwise
393 the setting will be ignored.</p>
395 <pre class="prettyprint lang-config"># Enable the X-Cache-Detail header
396 CacheDetailHeader on</pre>
399 <div class="example"><p><code>
400 X-Cache-Detail: "conditional cache hit: entity refreshed" from localhost<br />
405 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
406 <div class="directive-section"><h2><a name="CacheDisable" id="CacheDisable">CacheDisable</a> <a name="cachedisable" id="cachedisable">Directive</a></h2>
407 <table class="directive">
408 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Disable caching of specified URLs</td></tr>
409 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDisable <var>url-string</var> | <var>on</var></code></td></tr>
410 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
411 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
412 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
414 <p>The <code class="directive">CacheDisable</code> directive instructs
415 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to <em>not</em> cache urls at or below
416 <var>url-string</var>.</p>
418 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">CacheDisable /local_files</pre>
421 <p>If used in a <code class="directive"><Location></code> directive,
422 the path needs to be specified below the Location, or if the word "on"
423 is used, caching for the whole location will be disabled.</p>
425 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config"><Location /foo>
427 </Location></pre>
430 <p>The <code>no-cache</code> environment variable can be set to
431 disable caching on a finer grained set of resources in versions
432 2.2.12 and later.</p>
437 <li><a href="../env.html">Environment Variables in Apache</a></li>
440 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
441 <div class="directive-section"><h2><a name="CacheEnable" id="CacheEnable">CacheEnable</a> <a name="cacheenable" id="cacheenable">Directive</a></h2>
442 <table class="directive">
443 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable caching of specified URLs using a specified storage
445 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheEnable <var>cache_type</var> [<var>url-string</var>]</code></td></tr>
446 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory</td></tr>
447 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
448 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
449 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>A url-string of '/' applied to forward proxy content in 2.2 and
452 <p>The <code class="directive">CacheEnable</code> directive instructs
453 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to cache urls at or below
454 <var>url-string</var>. The cache storage manager is specified with the
455 <var>cache_type</var> argument. The <code class="directive">CacheEnable</code>
456 directive can alternatively be placed inside either
457 <code class="directive"><Location></code> or
458 <code class="directive"><LocationMatch></code> sections to indicate
459 the content is cacheable.
460 <var>cache_type</var> <code>disk</code> instructs
461 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the disk based storage manager
462 implemented by <code class="module"><a href="../mod/mod_cache_disk.html">mod_cache_disk</a></code>. <var>cache_type</var>
463 <code>socache</code> instructs <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the
464 shared object cache based storage manager implemented by
465 <code class="module"><a href="../mod/mod_cache_socache.html">mod_cache_socache</a></code>.</p>
466 <p>In the event that the URL space overlaps between different
467 <code class="directive">CacheEnable</code> directives (as in the example below),
468 each possible storage manager will be run until the first one that
469 actually processes the request. The order in which the storage managers are
470 run is determined by the order of the <code class="directive">CacheEnable</code>
471 directives in the configuration file. <code class="directive">CacheEnable</code>
472 directives within <code class="directive"><Location></code> or
473 <code class="directive"><LocationMatch></code> sections are processed
474 before globally defined <code class="directive">CacheEnable</code> directives.</p>
476 <p>When acting as a forward proxy server, <var>url-string</var> must
477 minimally begin with a protocol for which caching should be enabled.</p>
479 <pre class="prettyprint lang-config"># Cache content (normal handler only)
480 CacheQuickHandler off
481 <Location /foo>
485 # Cache regex (normal handler only)
486 CacheQuickHandler off
487 <LocationMatch foo$>
489 </LocationMatch>
491 # Cache all but forward proxy url's (normal or quick handler)
494 # Cache FTP-proxied url's (normal or quick handler)
495 CacheEnable disk ftp://
497 # Cache forward proxy content from www.example.org (normal or quick handler)
498 CacheEnable disk http://www.example.org/</pre>
501 <p>A hostname starting with a <strong>"*"</strong> matches all hostnames with
502 that suffix. A hostname starting with <strong>"."</strong> matches all
503 hostnames containing the domain components that follow.</p>
505 <pre class="prettyprint lang-config"># Match www.example.org, and fooexample.org
506 CacheEnable disk http://*example.org/
507 # Match www.example.org, but not fooexample.org
508 CacheEnable disk http://.example.org/</pre>
511 <p> The <code>no-cache</code> environment variable can be set to
512 disable caching on a finer grained set of resources in versions
513 2.2.12 and later.</p>
518 <li><a href="../env.html">Environment Variables in Apache</a></li>
521 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
522 <div class="directive-section"><h2><a name="CacheHeader" id="CacheHeader">CacheHeader</a> <a name="cacheheader" id="cacheheader">Directive</a></h2>
523 <table class="directive">
524 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Add an X-Cache header to the response.</td></tr>
525 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheHeader <var>on|off</var></code></td></tr>
526 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheHeader off</code></td></tr>
527 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
528 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
529 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
530 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr>
532 <p>When the <code class="directive"><a href="#cacheheader">CacheHeader</a></code> directive
533 is switched on, an <strong>X-Cache</strong> header will be added to the response
534 with the cache status of this response. If the normal handler is used, this
535 directive may appear within a <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code>
536 or <code class="directive"><a href="../mod/core.html#location"><Location></a></code> directive. If the quick
537 handler is used, this directive must appear within a server or virtual host
538 context, otherwise the setting will be ignored.</p>
541 <dt><strong>HIT</strong></dt><dd>The entity was fresh, and was served from
543 <dt><strong>REVALIDATE</strong></dt><dd>The entity was stale, was successfully
544 revalidated and was served from cache.</dd>
545 <dt><strong>MISS</strong></dt><dd>The entity was fetched from the upstream
546 server and was not served from cache.</dd>
549 <pre class="prettyprint lang-config"># Enable the X-Cache header
553 <pre class="prettyprint lang-config">X-Cache: HIT from localhost</pre>
558 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
559 <div class="directive-section"><h2><a name="CacheIgnoreCacheControl" id="CacheIgnoreCacheControl">CacheIgnoreCacheControl</a> <a name="cacheignorecachecontrol" id="cacheignorecachecontrol">Directive</a></h2>
560 <table class="directive">
561 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore request to not serve cached content to client</td></tr>
562 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreCacheControl On|Off</code></td></tr>
563 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreCacheControl Off</code></td></tr>
564 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
565 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
566 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
568 <p>Ordinarily, requests containing a Cache-Control: no-cache or
569 Pragma: no-cache header value will not be served from the cache. The
570 <code class="directive">CacheIgnoreCacheControl</code> directive allows this
571 behavior to be overridden. <code class="directive">CacheIgnoreCacheControl On</code>
572 tells the server to attempt to serve the resource from the cache even
573 if the request contains no-cache header values.</p>
575 <pre class="prettyprint lang-config">CacheIgnoreCacheControl On</pre>
578 <div class="warning"><h3>Warning:</h3>
579 This directive will allow serving from the cache even if the client has
580 requested that the document not be served from the cache. This might
581 result in stale content being served.
586 <li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li>
587 <li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li>
590 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
591 <div class="directive-section"><h2><a name="CacheIgnoreHeaders" id="CacheIgnoreHeaders">CacheIgnoreHeaders</a> <a name="cacheignoreheaders" id="cacheignoreheaders">Directive</a></h2>
592 <table class="directive">
593 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Do not store the given HTTP header(s) in the cache.
595 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreHeaders <var>header-string</var> [<var>header-string</var>] ...</code></td></tr>
596 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreHeaders None</code></td></tr>
597 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
598 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
599 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
601 <p>According to RFC 2616, hop-by-hop HTTP headers are not stored in
602 the cache. The following HTTP headers are hop-by-hop headers and thus
603 do not get stored in the cache in <em>any</em> case regardless of the
604 setting of <code class="directive">CacheIgnoreHeaders</code>:</p>
607 <li><code>Connection</code></li>
608 <li><code>Keep-Alive</code></li>
609 <li><code>Proxy-Authenticate</code></li>
610 <li><code>Proxy-Authorization</code></li>
611 <li><code>TE</code></li>
612 <li><code>Trailers</code></li>
613 <li><code>Transfer-Encoding</code></li>
614 <li><code>Upgrade</code></li>
617 <p><code class="directive">CacheIgnoreHeaders</code> specifies additional HTTP
618 headers that should not to be stored in the cache. For example, it makes
619 sense in some cases to prevent cookies from being stored in the cache.</p>
621 <p><code class="directive">CacheIgnoreHeaders</code> takes a space separated list
622 of HTTP headers that should not be stored in the cache. If only hop-by-hop
623 headers not should be stored in the cache (the RFC 2616 compliant
624 behaviour), <code class="directive">CacheIgnoreHeaders</code> can be set to
625 <code>None</code>.</p>
627 <div class="example"><h3>Example 1</h3><pre class="prettyprint lang-config">CacheIgnoreHeaders Set-Cookie</pre>
630 <div class="example"><h3>Example 2</h3><pre class="prettyprint lang-config">CacheIgnoreHeaders None</pre>
633 <div class="warning"><h3>Warning:</h3>
634 If headers like <code>Expires</code> which are needed for proper cache
635 management are not stored due to a
636 <code class="directive">CacheIgnoreHeaders</code> setting, the behaviour of
637 mod_cache is undefined.
641 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
642 <div class="directive-section"><h2><a name="CacheIgnoreNoLastMod" id="CacheIgnoreNoLastMod">CacheIgnoreNoLastMod</a> <a name="cacheignorenolastmod" id="cacheignorenolastmod">Directive</a></h2>
643 <table class="directive">
644 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore the fact that a response has no Last Modified
646 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreNoLastMod On|Off</code></td></tr>
647 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreNoLastMod Off</code></td></tr>
648 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
649 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
650 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
652 <p>Ordinarily, documents without a last-modified date are not cached.
653 Under some circumstances the last-modified date is removed (during
654 <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> processing for example) or not provided
655 at all. The <code class="directive">CacheIgnoreNoLastMod</code> directive
656 provides a way to specify that documents without last-modified dates
657 should be considered for caching, even without a last-modified date.
658 If neither a last-modified date nor an expiry date are provided with
659 the document then the value specified by the
660 <code class="directive">CacheDefaultExpire</code> directive will be used to
661 generate an expiration date.</p>
663 <pre class="prettyprint lang-config">CacheIgnoreNoLastMod On</pre>
667 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
668 <div class="directive-section"><h2><a name="CacheIgnoreQueryString" id="CacheIgnoreQueryString">CacheIgnoreQueryString</a> <a name="cacheignorequerystring" id="cacheignorequerystring">Directive</a></h2>
669 <table class="directive">
670 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore query string when caching</td></tr>
671 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreQueryString On|Off</code></td></tr>
672 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreQueryString Off</code></td></tr>
673 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
674 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
675 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
677 <p>Ordinarily, requests with query string parameters are cached separately
678 for each unique query string. This is according to RFC 2616/13.9 done only
679 if an expiration time is specified. The
680 <code class="directive">CacheIgnoreQueryString</code> directive tells the cache to
681 cache requests even if no expiration time is specified, and to reply with
682 a cached reply even if the query string differs. From a caching point of
683 view the request is treated as if having no query string when this
684 directive is enabled.</p>
686 <pre class="prettyprint lang-config">CacheIgnoreQueryString On</pre>
691 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
692 <div class="directive-section"><h2><a name="CacheIgnoreURLSessionIdentifiers" id="CacheIgnoreURLSessionIdentifiers">CacheIgnoreURLSessionIdentifiers</a> <a name="cacheignoreurlsessionidentifiers" id="cacheignoreurlsessionidentifiers">Directive</a></h2>
693 <table class="directive">
694 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore defined session identifiers encoded in the URL when caching
696 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreURLSessionIdentifiers <var>identifier</var> [<var>identifier</var>] ...</code></td></tr>
697 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreURLSessionIdentifiers None</code></td></tr>
698 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
699 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
700 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
702 <p>Sometimes applications encode the session identifier into the URL like in the following
706 <li><code>/someapplication/image.gif;jsessionid=123456789</code></li>
707 <li><code>/someapplication/image.gif?PHPSESSIONID=12345678</code></li>
709 <p>This causes cachable resources to be stored separately for each session, which
710 is often not desired. <code class="directive">CacheIgnoreURLSessionIdentifiers</code> lets
711 define a list of identifiers that are removed from the key that is used to identify
712 an entity in the cache, such that cachable resources are not stored separately for
715 <p><code>CacheIgnoreURLSessionIdentifiers None</code> clears the list of ignored
716 identifiers. Otherwise, each identifier is added to the list.</p>
718 <div class="example"><h3>Example 1</h3><pre class="prettyprint lang-config">CacheIgnoreURLSessionIdentifiers jsessionid</pre>
721 <div class="example"><h3>Example 2</h3><pre class="prettyprint lang-config">CacheIgnoreURLSessionIdentifiers None</pre>
726 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
727 <div class="directive-section"><h2><a name="CacheKeyBaseURL" id="CacheKeyBaseURL">CacheKeyBaseURL</a> <a name="cachekeybaseurl" id="cachekeybaseurl">Directive</a></h2>
728 <table class="directive">
729 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Override the base URL of reverse proxied cache keys.</td></tr>
730 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheKeyBaseURL <var>URL</var></code></td></tr>
731 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheKeyBaseURL http://example.com</code></td></tr>
732 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
733 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
734 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
735 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr>
737 <p>When the <code class="directive"><a href="#cachekeybaseurl">CacheKeyBaseURL</a></code> directive
738 is specified, the URL provided will be used as the base URL to calculate
739 the URL of the cache keys in the reverse proxy configuration. When not specified,
740 the scheme, hostname and port of the current virtual host is used to construct
741 the cache key. When a cluster of machines is present, and all cached entries
742 should be cached beneath the same cache key, a new base URL can be specified
743 with this directive.</p>
745 <pre class="prettyprint lang-config"># Override the base URL of the cache key.
746 CacheKeyBaseURL http://www.example.com/</pre>
749 <div class="warning">Take care when setting this directive. If two separate virtual
750 hosts are accidentally given the same base URL, entries from one virtual host
751 will be served to the other.</div>
755 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
756 <div class="directive-section"><h2><a name="CacheLastModifiedFactor" id="CacheLastModifiedFactor">CacheLastModifiedFactor</a> <a name="cachelastmodifiedfactor" id="cachelastmodifiedfactor">Directive</a></h2>
757 <table class="directive">
758 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The factor used to compute an expiry date based on the
759 LastModified date.</td></tr>
760 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLastModifiedFactor <var>float</var></code></td></tr>
761 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLastModifiedFactor 0.1</code></td></tr>
762 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
763 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
764 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
766 <p>In the event that a document does not provide an expiry date but does
767 provide a last-modified date, an expiry date can be calculated based on
768 the time since the document was last modified. The
769 <code class="directive">CacheLastModifiedFactor</code> directive specifies a
770 <var>factor</var> to be used in the generation of this expiry date
771 according to the following formula:
773 <code>expiry-period = time-since-last-modified-date * <var>factor</var>
774 expiry-date = current-date + expiry-period</code>
776 For example, if the document was last modified 10 hours ago, and
777 <var>factor</var> is 0.1 then the expiry-period will be set to
778 10*0.1 = 1 hour. If the current time was 3:00pm then the computed
779 expiry-date would be 3:00pm + 1hour = 4:00pm.
781 If the expiry-period would be longer than that set by
782 <code class="directive">CacheMaxExpire</code>, then the latter takes
785 <pre class="prettyprint lang-config">CacheLastModifiedFactor 0.5</pre>
789 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
790 <div class="directive-section"><h2><a name="CacheLock" id="CacheLock">CacheLock</a> <a name="cachelock" id="cachelock">Directive</a></h2>
791 <table class="directive">
792 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable the thundering herd lock.</td></tr>
793 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLock <var>on|off</var></code></td></tr>
794 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLock off</code></td></tr>
795 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
796 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
797 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
799 <p>The <code class="directive">CacheLock</code> directive enables the thundering herd lock
800 for the given URL space.</p>
802 <p>In a minimal configuration the following directive is all that is needed to
803 enable the thundering herd lock in the default run-time file directory.</p>
805 <pre class="prettyprint lang-config"># Enable cache lock
809 <p>Locks consist of empty files that only exist for stale URLs in flight, so this
810 is significantly less resource intensive than the traditional disk cache.</p>
813 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
814 <div class="directive-section"><h2><a name="CacheLockMaxAge" id="CacheLockMaxAge">CacheLockMaxAge</a> <a name="cachelockmaxage" id="cachelockmaxage">Directive</a></h2>
815 <table class="directive">
816 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the maximum possible age of a cache lock.</td></tr>
817 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockMaxAge <var>integer</var></code></td></tr>
818 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockMaxAge 5</code></td></tr>
819 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
820 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
821 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
823 <p>The <code class="directive">CacheLockMaxAge</code> directive specifies the maximum
824 age of any cache lock.</p>
826 <p>A lock older than this value in seconds will be ignored, and the next
827 incoming request will be given the opportunity to re-establish the lock.
828 This mechanism prevents a slow client taking an excessively long time to refresh
833 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
834 <div class="directive-section"><h2><a name="CacheLockPath" id="CacheLockPath">CacheLockPath</a> <a name="cachelockpath" id="cachelockpath">Directive</a></h2>
835 <table class="directive">
836 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the lock path directory.</td></tr>
837 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockPath <var>directory</var></code></td></tr>
838 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockPath mod_cache-lock</code></td></tr>
839 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
840 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
841 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
843 <p>The <code class="directive">CacheLockPath</code> directive allows you to specify the
844 directory in which the locks are created. If <var>directory</var> is not an absolute
845 path, the location specified will be relative to the value of
846 <code class="directive"><a href="../mod/core.html#defaultruntimedir">DefaultRuntimeDir</a></code>.</p>
849 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
850 <div class="directive-section"><h2><a name="CacheMaxExpire" id="CacheMaxExpire">CacheMaxExpire</a> <a name="cachemaxexpire" id="cachemaxexpire">Directive</a></h2>
851 <table class="directive">
852 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum time in seconds to cache a document</td></tr>
853 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMaxExpire <var>seconds</var></code></td></tr>
854 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMaxExpire 86400 (one day)</code></td></tr>
855 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
856 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
857 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
859 <p>The <code class="directive">CacheMaxExpire</code> directive specifies the maximum number of
860 seconds for which cachable HTTP documents will be retained without checking the origin
861 server. Thus, documents will be out of date at most this number of seconds. This maximum
862 value is enforced even if an expiry date was supplied with the document.</p>
864 <pre class="prettyprint lang-config">CacheMaxExpire 604800</pre>
868 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
869 <div class="directive-section"><h2><a name="CacheMinExpire" id="CacheMinExpire">CacheMinExpire</a> <a name="cacheminexpire" id="cacheminexpire">Directive</a></h2>
870 <table class="directive">
871 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The minimum time in seconds to cache a document</td></tr>
872 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMinExpire <var>seconds</var></code></td></tr>
873 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMinExpire 0</code></td></tr>
874 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
875 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
876 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
878 <p>The <code class="directive">CacheMinExpire</code> directive specifies the minimum number of
879 seconds for which cachable HTTP documents will be retained without checking the origin
880 server. This is only used if no valid expire time was supplied with the document.</p>
883 <pre class="prettyprint lang-config">CacheMinExpire 3600</pre>
887 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
888 <div class="directive-section"><h2><a name="CacheQuickHandler" id="CacheQuickHandler">CacheQuickHandler</a> <a name="cachequickhandler" id="cachequickhandler">Directive</a></h2>
889 <table class="directive">
890 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Run the cache from the quick handler.</td></tr>
891 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheQuickHandler <var>on|off</var></code></td></tr>
892 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheQuickHandler on</code></td></tr>
893 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
894 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
895 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
896 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Apache HTTP Server 2.3.3 and later</td></tr>
898 <p>The <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code> directive
899 controls the phase in which the cache is handled.</p>
901 <p>In the default enabled configuration, the cache operates within the quick
902 handler phase. This phase short circuits the majority of server processing,
903 and represents the most performant mode of operation for a typical server.
904 The cache <strong>bolts onto</strong> the front of the server, and the
905 majority of server processing is avoided.</p>
907 <p>When disabled, the cache operates as a normal handler, and is subject to
908 the full set of phases when handling a server request. While this mode is
909 slower than the default, it allows the cache to be used in cases where full
910 processing is required, such as when content is subject to authorization.</p>
912 <pre class="prettyprint lang-config"># Run cache as a normal handler
913 CacheQuickHandler off</pre>
916 <p>It is also possible, when the quick handler is disabled, for the
917 administrator to choose the precise location within the filter chain where
918 caching is to be performed, by adding the <strong>CACHE</strong> filter to
921 <pre class="prettyprint lang-config"># Cache content before mod_include and mod_deflate
922 CacheQuickHandler off
923 AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html</pre>
926 <p>If the CACHE filter is specified more than once, the last instance will
931 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
932 <div class="directive-section"><h2><a name="CacheStaleOnError" id="CacheStaleOnError">CacheStaleOnError</a> <a name="cachestaleonerror" id="cachestaleonerror">Directive</a></h2>
933 <table class="directive">
934 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Serve stale content in place of 5xx responses.</td></tr>
935 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStaleOnError <var>on|off</var></code></td></tr>
936 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStaleOnError on</code></td></tr>
937 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
938 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
939 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
940 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr>
942 <p>When the <code class="directive"><a href="#cachestaleonerror">CacheStaleOnError</a></code> directive
943 is switched on, and when stale data is available in the cache, the cache will
944 respond to 5xx responses from the backend by returning the stale data instead of
945 the 5xx response. While the Cache-Control headers sent by clients will be respected,
946 and the raw 5xx responses returned to the client on request, the 5xx response so
947 returned to the client will not invalidate the content in the cache.</p>
949 <pre class="prettyprint lang-config"># Serve stale data on error.
950 CacheStaleOnError on</pre>
955 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
956 <div class="directive-section"><h2><a name="CacheStoreExpired" id="CacheStoreExpired">CacheStoreExpired</a> <a name="cachestoreexpired" id="cachestoreexpired">Directive</a></h2>
957 <table class="directive">
958 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Attempt to cache responses that the server reports as expired</td></tr>
959 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStoreExpired On|Off</code></td></tr>
960 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStoreExpired Off</code></td></tr>
961 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
962 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
963 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
965 <p>Since httpd 2.2.4, responses which have already expired are not
966 stored in the cache. The <code class="directive">CacheStoreExpired</code>
967 directive allows this behavior to be overridden.
968 <code class="directive">CacheStoreExpired</code> On
969 tells the server to attempt to cache the resource if it is stale.
970 Subsequent requests would trigger an If-Modified-Since request of
971 the origin server, and the response may be fulfilled from cache
972 if the backend resource has not changed.</p>
974 <pre class="prettyprint lang-config">CacheStoreExpired On</pre>
978 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
979 <div class="directive-section"><h2><a name="CacheStoreNoStore" id="CacheStoreNoStore">CacheStoreNoStore</a> <a name="cachestorenostore" id="cachestorenostore">Directive</a></h2>
980 <table class="directive">
981 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Attempt to cache requests or responses that have been marked as no-store.</td></tr>
982 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStoreNoStore On|Off</code></td></tr>
983 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStoreNoStore Off</code></td></tr>
984 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
985 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
986 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
988 <p>Ordinarily, requests or responses with Cache-Control: no-store header
989 values will not be stored in the cache. The
990 <code class="directive">CacheStoreNoStore</code> directive allows this
991 behavior to be overridden. <code class="directive">CacheStoreNoStore</code> On
992 tells the server to attempt to cache the resource even if it contains
993 no-store header values.</p>
995 <pre class="prettyprint lang-config">CacheStoreNoStore On</pre>
998 <div class="warning"><h3>Warning:</h3>
999 As described in RFC 2616, the no-store directive is intended to
1000 "prevent the inadvertent release or retention of sensitive information
1001 (for example, on backup tapes)." Enabling this option could store
1002 sensitive information in the cache. You are hereby warned.
1007 <li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li>
1008 <li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li>
1011 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
1012 <div class="directive-section"><h2><a name="CacheStorePrivate" id="CacheStorePrivate">CacheStorePrivate</a> <a name="cachestoreprivate" id="cachestoreprivate">Directive</a></h2>
1013 <table class="directive">
1014 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Attempt to cache responses that the server has marked as private</td></tr>
1015 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStorePrivate On|Off</code></td></tr>
1016 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStorePrivate Off</code></td></tr>
1017 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
1018 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
1019 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
1021 <p>Ordinarily, responses with Cache-Control: private header values will not
1022 be stored in the cache. The <code class="directive">CacheStorePrivate</code>
1023 directive allows this behavior to be overridden.
1024 <code class="directive">CacheStorePrivate</code> On
1025 tells the server to attempt to cache the resource even if it contains
1026 private header values.</p>
1028 <pre class="prettyprint lang-config">CacheStorePrivate On</pre>
1031 <div class="warning"><h3>Warning:</h3>
1032 This directive will allow caching even if the upstream server has
1033 requested that the resource not be cached. This directive is only
1034 ideal for a 'private' cache.
1039 <li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li>
1040 <li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li>
1044 <div class="bottomlang">
1045 <p><span>Available Languages: </span><a href="../en/mod/mod_cache.html" title="English"> en </a> |
1046 <a href="../fr/mod/mod_cache.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
1047 <a href="../ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
1048 <a href="../ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
1049 </div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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