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26 <div id="page-content">
27 <div id="preamble"><h1>Apache Module mod_cache</h1>
29 <p><span>Available Languages: </span><a href="../en/mod/mod_cache.html" title="English"> en </a> |
30 <a href="../fr/mod/mod_cache.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
31 <a href="../ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
32 <a href="../ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
34 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>RFC 2616 compliant HTTP caching filter.</td></tr>
35 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
36 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>cache_module</td></tr>
37 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_cache.c</td></tr></table>
40 <div class="warning">This module should be used with care, as when the
41 <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code> directive is
42 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.
43 You should not enable quick handler caching for any content to which you
44 wish to limit access by client host name, address or environment
47 <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
48 <strong>HTTP content caching filter</strong>, with support for the caching
49 of content negotiated responses containing the Vary header.</p>
51 <p>RFC 2616 compliant caching provides a mechanism to verify whether
52 stale or expired content is still fresh, and can represent a significant
53 performance boost when the origin server supports <strong>conditional
54 requests</strong> by honouring the
55 <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26">If-None-Match</a>
56 HTTP request header. Content is only regenerated from scratch when the content
57 has changed, and not when the cached entry expires.</p>
59 <p>As a filter, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> can be placed in front of
60 content originating from any handler, including <strong>flat
61 files</strong> (served from a slow disk cached on a fast disk), the output
62 of a <strong>CGI script</strong> or <strong>dynamic content
63 generator</strong>, or content <strong>proxied from another
66 <p>In the default configuration, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> inserts the
67 caching filter as far forward as possible within the filter stack,
68 utilising the <strong>quick handler</strong> to bypass all per request
69 processing when returning content to the client. In this mode of
70 operation, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> may be thought of as a caching
71 proxy server bolted to the front of the webserver, while running within
72 the webserver itself.</p>
74 <p>When the quick handler is switched off using the
75 <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code> directive,
76 it becomes possible to insert the <strong>CACHE</strong> filter at a
77 point in the filter stack chosen by the administrator. This provides the
78 opportunity to cache content before that content is personalised by the
79 <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> filter, or optionally compressed by the
80 <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> filter.</p>
82 <p>Under normal operation, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> will respond to
83 and can be controlled by the
84 <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9">Cache-Control</a>
86 <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.32">Pragma</a>
87 headers sent from a client in a request, or from a
88 server within a response. Under exceptional circumstances,
89 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> can be configured to override these headers
90 and force site specific behaviour, however such behaviour will be limited
91 to this cache only, and will not affect the operation of other caches
92 that may exist between the client and server, and as a result is not
93 recommended unless strictly necessary.</p>
95 <p>RFC 2616 allows for the cache to return stale data while the existing
96 stale entry is refreshed from the origin server, and this is supported
97 by <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> when the
98 <code class="directive"><a href="#cachelock">CacheLock</a></code> directive is suitably
99 configured. Such responses will contain a
100 <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.46">Warning</a>
101 HTTP header with a 110 response code. RFC 2616 also allows a cache to return
102 stale data when the attempt made to refresh the stale data returns an
103 error 500 or above, and this behaviour is supported by default by
104 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>. Such responses will contain a
105 <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.46">Warning</a>
106 HTTP header with a 111 response code.</p>
108 <p><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> requires the services of one or more
109 storage management modules. The following storage management modules are included in
110 the base Apache distribution:</p>
112 <dt><code class="module"><a href="../mod/mod_cache_disk.html">mod_cache_disk</a></code></dt>
113 <dd>Implements a disk based storage manager. Headers and bodies are
114 stored separately on disk, in a directory structure derived from the
115 md5 hash of the cached URL. Multiple content negotiated responses can
116 be stored concurrently, however the caching of partial content is not
117 supported by this module. The <code class="program"><a href="../programs/htcacheclean.html">htcacheclean</a></code> tool is
118 provided to list cached URLs, remove cached URLs, or to maintain the size
119 of the disk cache within size and inode limits.</dd>
120 <dt><code class="module"><a href="../mod/mod_cache_socache.html">mod_cache_socache</a></code></dt>
121 <dd>Implements a shared object cache based storage manager. Headers and
122 bodies are stored together beneath a single key based on the URL of the
123 response being cached. Multiple content negotiated responses can
124 be stored concurrently, however the caching of partial content is not
125 supported by this module.</dd>
128 <p>Further details, discussion, and examples, are provided in the
129 <a href="../caching.html">Caching Guide</a>.</p>
131 <div id="quickview"><h3>Topics</h3>
133 <li><img alt="" src="../images/down.gif" /> <a href="#related">Related Modules and Directives</a></li>
134 <li><img alt="" src="../images/down.gif" /> <a href="#sampleconf">Sample Configuration</a></li>
135 <li><img alt="" src="../images/down.gif" /> <a href="#thunderingherd">Avoiding the Thundering Herd</a></li>
136 <li><img alt="" src="../images/down.gif" /> <a href="#finecontrol">Fine Control with the CACHE Filter</a></li>
137 <li><img alt="" src="../images/down.gif" /> <a href="#status">Cache Status and Logging</a></li>
138 </ul><h3 class="directives">Directives</h3>
140 <li><img alt="" src="../images/down.gif" /> <a href="#cachedefaultexpire">CacheDefaultExpire</a></li>
141 <li><img alt="" src="../images/down.gif" /> <a href="#cachedetailheader">CacheDetailHeader</a></li>
142 <li><img alt="" src="../images/down.gif" /> <a href="#cachedisable">CacheDisable</a></li>
143 <li><img alt="" src="../images/down.gif" /> <a href="#cacheenable">CacheEnable</a></li>
144 <li><img alt="" src="../images/down.gif" /> <a href="#cacheheader">CacheHeader</a></li>
145 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></li>
146 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignoreheaders">CacheIgnoreHeaders</a></li>
147 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignorenolastmod">CacheIgnoreNoLastMod</a></li>
148 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignorequerystring">CacheIgnoreQueryString</a></li>
149 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignoreurlsessionidentifiers">CacheIgnoreURLSessionIdentifiers</a></li>
150 <li><img alt="" src="../images/down.gif" /> <a href="#cachekeybaseurl">CacheKeyBaseURL</a></li>
151 <li><img alt="" src="../images/down.gif" /> <a href="#cachelastmodifiedfactor">CacheLastModifiedFactor</a></li>
152 <li><img alt="" src="../images/down.gif" /> <a href="#cachelock">CacheLock</a></li>
153 <li><img alt="" src="../images/down.gif" /> <a href="#cachelockmaxage">CacheLockMaxAge</a></li>
154 <li><img alt="" src="../images/down.gif" /> <a href="#cachelockpath">CacheLockPath</a></li>
155 <li><img alt="" src="../images/down.gif" /> <a href="#cachemaxexpire">CacheMaxExpire</a></li>
156 <li><img alt="" src="../images/down.gif" /> <a href="#cacheminexpire">CacheMinExpire</a></li>
157 <li><img alt="" src="../images/down.gif" /> <a href="#cachequickhandler">CacheQuickHandler</a></li>
158 <li><img alt="" src="../images/down.gif" /> <a href="#cachestaleonerror">CacheStaleOnError</a></li>
159 <li><img alt="" src="../images/down.gif" /> <a href="#cachestoreexpired">CacheStoreExpired</a></li>
160 <li><img alt="" src="../images/down.gif" /> <a href="#cachestorenostore">CacheStoreNoStore</a></li>
161 <li><img alt="" src="../images/down.gif" /> <a href="#cachestoreprivate">CacheStorePrivate</a></li>
163 <h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mod_cache">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mod_cache">Report a bug</a></li></ul><h3>See also</h3>
165 <li><a href="../caching.html">Caching Guide</a></li>
166 <li><a href="#comments_section">Comments</a></li></ul></div>
167 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
168 <div class="section">
169 <h2><a name="related" id="related">Related Modules and Directives</a></h2>
170 <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>
171 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
172 <div class="section">
173 <h2><a name="sampleconf" id="sampleconf">Sample Configuration</a></h2>
174 <div class="example"><h3>Sample httpd.conf</h3><pre class="prettyprint lang-config">#
175 # Sample Cache Configuration
177 LoadModule cache_module modules/mod_cache.so
178 <IfModule mod_cache.c>
179 LoadModule cache_disk_module modules/mod_cache_disk.so
180 <IfModule mod_cache_disk.c>
181 CacheRoot c:/cacheroot
187 # When acting as a proxy, don't cache the list of security updates
188 CacheDisable http://security.update.server/update-list/
189 </IfModule></pre>
191 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
192 <div class="section">
193 <h2><a name="thunderingherd" id="thunderingherd">Avoiding the Thundering Herd</a></h2>
194 <p>When a cached entry becomes stale, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> will submit
195 a conditional request to the backend, which is expected to confirm whether the
196 cached entry is still fresh, and send an updated entity if not.</p>
197 <p>A small but finite amount of time exists between the time the cached entity
198 becomes stale, and the time the stale entity is fully refreshed. On a busy
199 server, a significant number of requests might arrive during this time, and
200 cause a <strong>thundering herd</strong> of requests to strike the backend
201 suddenly and unpredictably.</p>
202 <p>To keep the thundering herd at bay, the <code class="directive">CacheLock</code>
203 directive can be used to define a directory in which locks are created for
204 URLs <strong>in flight</strong>. The lock is used as a <strong>hint</strong>
205 by other requests to either suppress an attempt to cache (someone else has
206 gone to fetch the entity), or to indicate that a stale entry is being refreshed
207 (stale content will be returned in the mean time).
209 <h3>Initial caching of an entry</h3>
211 <p>When an entity is cached for the first time, a lock will be created for the
212 entity until the response has been fully cached. During the lifetime of the
213 lock, the cache will suppress the second and subsequent attempt to cache the
214 same entity. While this doesn't hold back the thundering herd, it does stop
215 the cache attempting to cache the same entity multiple times simultaneously.
218 <h3>Refreshment of a stale entry</h3>
220 <p>When an entity reaches its freshness lifetime and becomes stale, a lock
221 will be created for the entity until the response has either been confirmed as
222 still fresh, or replaced by the backend. During the lifetime of the lock, the
223 second and subsequent incoming request will cause stale data to be returned,
224 and the thundering herd is kept at bay.</p>
226 <h3>Locks and Cache-Control: no-cache</h3>
228 <p>Locks are used as a <strong>hint only</strong> to enable the cache to be
229 more gentle on backend servers, however the lock can be overridden if necessary.
230 If the client sends a request with a Cache-Control header forcing a reload, any
231 lock that may be present will be ignored, and the client's request will be
232 honored immediately and the cached entry refreshed.</p>
233 <p>As a further safety mechanism, locks have a configurable maximum age.
234 Once this age has been reached, the lock is removed, and a new request is
235 given the opportunity to create a new lock. This maximum age can be set using
236 the <code class="directive">CacheLockMaxAge</code> directive, and defaults to 5
240 <h3>Example configuration</h3>
242 <div class="example"><h3>Enabling the cache lock</h3><pre class="prettyprint lang-config">#
243 # Enable the cache lock
245 <IfModule mod_cache.c>
247 CacheLockPath /tmp/mod_cache-lock
249 </IfModule></pre>
252 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
253 <div class="section">
254 <h2><a name="finecontrol" id="finecontrol">Fine Control with the CACHE Filter</a></h2>
255 <p>Under the default mode of cache operation, the cache runs as a quick handler,
256 short circuiting the majority of server processing and offering the highest
257 cache performance available.</p>
259 <p>In this mode, the cache <strong>bolts onto</strong> the front of the server,
260 acting as if a free standing RFC 2616 caching proxy had been placed in front of
263 <p>While this mode offers the best performance, the administrator may find that
264 under certain circumstances they may want to perform further processing on the
265 request after the request is cached, such as to inject personalisation into the
266 cached page, or to apply authorization restrictions to the content. Under these
267 circumstances, an administrator is often forced to place independent reverse
268 proxy servers either behind or in front of the caching server to achieve this.</p>
270 <p>To solve this problem the <code class="directive"><a href="#cachequickhandler">CacheQuickHandler
271 </a></code> directive can be set to <strong>off</strong>, and the server will
272 process all phases normally handled by a non-cached request, including the
273 <strong>authentication and authorization</strong> phases.</p>
275 <p>In addition, the administrator may optionally specify the <strong>precise point
276 within the filter chain</strong> where caching is to take place by adding the
277 <strong>CACHE</strong> filter to the output filter chain.</p>
279 <p>For example, to cache content before applying compression to the response,
280 place the <strong>CACHE</strong> filter before the <strong>DEFLATE</strong>
281 filter as in the example below:</p>
283 <pre class="prettyprint lang-config"># Cache content before optional compression
284 CacheQuickHandler off
285 AddOutputFilterByType CACHE;DEFLATE text/plain</pre>
288 <p>Another option is to have content cached before personalisation is applied
289 by <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> (or another content processing filter). In this
290 example templates containing tags understood by
291 <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> are cached before being parsed:</p>
293 <pre class="prettyprint lang-config"># Cache content before mod_include and mod_deflate
294 CacheQuickHandler off
295 AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html</pre>
298 <p>You may place the <strong>CACHE</strong> filter anywhere you wish within the
299 filter chain. In this example, content is cached after being parsed by
300 <code class="module"><a href="../mod/mod_include.html">mod_include</a></code>, but before being processed by
301 <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code>:</p>
303 <pre class="prettyprint lang-config"># Cache content between mod_include and mod_deflate
304 CacheQuickHandler off
305 AddOutputFilterByType INCLUDES;CACHE;DEFLATE text/html</pre>
308 <div class="warning"><h3>Warning:</h3>If the location of the
309 <strong>CACHE</strong> filter in the filter chain is changed for any reason,
310 you may need to <strong>flush your cache</strong> to ensure that your data
311 served remains consistent. <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> is not in a position
312 to enforce this for you.</div>
314 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
315 <div class="section">
316 <h2><a name="status" id="status">Cache Status and Logging</a></h2>
317 <p>Once <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> has made a decision as to whether or not
318 an entity is to be served from cache, the detailed reason for the decision
319 is written to the subprocess environment within the request under the
320 <strong>cache-status</strong> key. This reason can be logged by the
321 <code class="directive"><a href="../mod/mod_log_config.html#logformat">LogFormat</a></code> directive as
324 <pre class="prettyprint lang-config">LogFormat "%{cache-status}e ..."</pre>
327 <p>Based on the caching decision made, the reason is also written to the
328 subprocess environment under one the following four keys, as appropriate:</p>
331 <dt>cache-hit</dt><dd>The response was served from cache.</dd>
332 <dt>cache-revalidate</dt><dd>The response was stale and was successfully
333 revalidated, then served from cache.</dd>
334 <dt>cache-miss</dt><dd>The response was served from the upstream server.</dd>
335 <dt>cache-invalidate</dt><dd>The cached entity was invalidated by a request
336 method other than GET or HEAD.</dd>
339 <p>This makes it possible to support conditional logging of cached requests
340 as per the following example:</p>
342 <pre class="prettyprint lang-config">CustomLog "cached-requests.log" common env=cache-hit
343 CustomLog "uncached-requests.log" common env=cache-miss
344 CustomLog "revalidated-requests.log" common env=cache-revalidate
345 CustomLog "invalidated-requests.log" common env=cache-invalidate</pre>
348 <p>For module authors, a hook called <var>cache_status</var> is available,
349 allowing modules to respond to the caching outcomes above in customised
352 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
353 <div class="directive-section"><h2><a name="CacheDefaultExpire" id="CacheDefaultExpire">CacheDefaultExpire</a> <a name="cachedefaultexpire" id="cachedefaultexpire">Directive</a></h2>
354 <table class="directive">
355 <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>
356 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDefaultExpire <var>seconds</var></code></td></tr>
357 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheDefaultExpire 3600 (one hour)</code></td></tr>
358 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
359 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
360 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
362 <p>The <code class="directive">CacheDefaultExpire</code> directive specifies a default time,
363 in seconds, to cache a document if neither an expiry date nor last-modified date are provided
364 with the document. The value specified with the <code class="directive">CacheMaxExpire</code>
365 directive does <em>not</em> override this setting.</p>
367 <pre class="prettyprint lang-config">CacheDefaultExpire 86400</pre>
371 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
372 <div class="directive-section"><h2><a name="CacheDetailHeader" id="CacheDetailHeader">CacheDetailHeader</a> <a name="cachedetailheader" id="cachedetailheader">Directive</a></h2>
373 <table class="directive">
374 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Add an X-Cache-Detail header to the response.</td></tr>
375 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDetailHeader <var>on|off</var></code></td></tr>
376 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheDetailHeader off</code></td></tr>
377 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
378 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
379 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
380 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr>
382 <p>When the <code class="directive"><a href="#cachedetailheader">CacheDetailHeader</a></code> directive
383 is switched on, an <strong>X-Cache-Detail</strong> header will be added to the response
384 containing the detailed reason for a particular caching decision.</p>
386 <p>It can be useful during development of cached RESTful services to have additional
387 information about the caching decision written to the response headers, so as to
388 confirm whether <code>Cache-Control</code> and other headers have been correctly
389 used by the service and client.</p>
391 <p>If the normal handler is used, this directive may appear within a
392 <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code> or
393 <code class="directive"><a href="../mod/core.html#location"><Location></a></code> directive. If the quick handler
394 is used, this directive must appear within a server or virtual host context, otherwise
395 the setting will be ignored.</p>
397 <pre class="prettyprint lang-config"># Enable the X-Cache-Detail header
398 CacheDetailHeader on</pre>
401 <div class="example"><p><code>
402 X-Cache-Detail: "conditional cache hit: entity refreshed" from localhost<br />
407 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
408 <div class="directive-section"><h2><a name="CacheDisable" id="CacheDisable">CacheDisable</a> <a name="cachedisable" id="cachedisable">Directive</a></h2>
409 <table class="directive">
410 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Disable caching of specified URLs</td></tr>
411 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDisable <var>url-string</var> | <var>on</var></code></td></tr>
412 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
413 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
414 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
416 <p>The <code class="directive">CacheDisable</code> directive instructs
417 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to <em>not</em> cache urls at or below
418 <var>url-string</var>.</p>
420 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">CacheDisable /local_files</pre>
423 <p>If used in a <code class="directive"><Location></code> directive,
424 the path needs to be specified below the Location, or if the word "on"
425 is used, caching for the whole location will be disabled.</p>
427 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config"><Location "/foo">
429 </Location></pre>
432 <p>The <code>no-cache</code> environment variable can be set to
433 disable caching on a finer grained set of resources in versions
434 2.2.12 and later.</p>
439 <li><a href="../env.html">Environment Variables in Apache</a></li>
442 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
443 <div class="directive-section"><h2><a name="CacheEnable" id="CacheEnable">CacheEnable</a> <a name="cacheenable" id="cacheenable">Directive</a></h2>
444 <table class="directive">
445 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable caching of specified URLs using a specified storage
447 <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>
448 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory</td></tr>
449 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
450 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
451 <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
454 <p>The <code class="directive">CacheEnable</code> directive instructs
455 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to cache urls at or below
456 <var>url-string</var>. The cache storage manager is specified with the
457 <var>cache_type</var> argument. The <code class="directive">CacheEnable</code>
458 directive can alternatively be placed inside either
459 <code class="directive"><Location></code> or
460 <code class="directive"><LocationMatch></code> sections to indicate
461 the content is cacheable.
462 <var>cache_type</var> <code>disk</code> instructs
463 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the disk based storage manager
464 implemented by <code class="module"><a href="../mod/mod_cache_disk.html">mod_cache_disk</a></code>. <var>cache_type</var>
465 <code>socache</code> instructs <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the
466 shared object cache based storage manager implemented by
467 <code class="module"><a href="../mod/mod_cache_socache.html">mod_cache_socache</a></code>.</p>
468 <p>In the event that the URL space overlaps between different
469 <code class="directive">CacheEnable</code> directives (as in the example below),
470 each possible storage manager will be run until the first one that
471 actually processes the request. The order in which the storage managers are
472 run is determined by the order of the <code class="directive">CacheEnable</code>
473 directives in the configuration file. <code class="directive">CacheEnable</code>
474 directives within <code class="directive"><Location></code> or
475 <code class="directive"><LocationMatch></code> sections are processed
476 before globally defined <code class="directive">CacheEnable</code> directives.</p>
478 <p>When acting as a forward proxy server, <var>url-string</var> must
479 minimally begin with a protocol for which caching should be enabled.</p>
481 <pre class="prettyprint lang-config"># Cache content (normal handler only)
482 CacheQuickHandler off
483 <Location "/foo">
487 # Cache regex (normal handler only)
488 CacheQuickHandler off
489 <LocationMatch "foo$">
491 </LocationMatch>
493 # Cache all but forward proxy url's (normal or quick handler)
496 # Cache FTP-proxied url's (normal or quick handler)
497 CacheEnable disk ftp://
499 # Cache forward proxy content from www.example.org (normal or quick handler)
500 CacheEnable disk http://www.example.org/</pre>
503 <p>A hostname starting with a <strong>"*"</strong> matches all hostnames with
504 that suffix. A hostname starting with <strong>"."</strong> matches all
505 hostnames containing the domain components that follow.</p>
507 <pre class="prettyprint lang-config"># Match www.example.org, and fooexample.org
508 CacheEnable disk http://*example.org/
509 # Match www.example.org, but not fooexample.org
510 CacheEnable disk http://.example.org/</pre>
513 <p> The <code>no-cache</code> environment variable can be set to
514 disable caching on a finer grained set of resources in versions
515 2.2.12 and later.</p>
520 <li><a href="../env.html">Environment Variables in Apache</a></li>
523 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
524 <div class="directive-section"><h2><a name="CacheHeader" id="CacheHeader">CacheHeader</a> <a name="cacheheader" id="cacheheader">Directive</a></h2>
525 <table class="directive">
526 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Add an X-Cache header to the response.</td></tr>
527 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheHeader <var>on|off</var></code></td></tr>
528 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheHeader off</code></td></tr>
529 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
530 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
531 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
532 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr>
534 <p>When the <code class="directive"><a href="#cacheheader">CacheHeader</a></code> directive
535 is switched on, an <strong>X-Cache</strong> header will be added to the response
536 with the cache status of this response. If the normal handler is used, this
537 directive may appear within a <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code>
538 or <code class="directive"><a href="../mod/core.html#location"><Location></a></code> directive. If the quick
539 handler is used, this directive must appear within a server or virtual host
540 context, otherwise the setting will be ignored.</p>
543 <dt><strong>HIT</strong></dt><dd>The entity was fresh, and was served from
545 <dt><strong>REVALIDATE</strong></dt><dd>The entity was stale, was successfully
546 revalidated and was served from cache.</dd>
547 <dt><strong>MISS</strong></dt><dd>The entity was fetched from the upstream
548 server and was not served from cache.</dd>
551 <pre class="prettyprint lang-config"># Enable the X-Cache header
555 <pre class="prettyprint lang-config">X-Cache: HIT from localhost</pre>
560 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
561 <div class="directive-section"><h2><a name="CacheIgnoreCacheControl" id="CacheIgnoreCacheControl">CacheIgnoreCacheControl</a> <a name="cacheignorecachecontrol" id="cacheignorecachecontrol">Directive</a></h2>
562 <table class="directive">
563 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore request to not serve cached content to client</td></tr>
564 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreCacheControl On|Off</code></td></tr>
565 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreCacheControl Off</code></td></tr>
566 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
567 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
568 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
570 <p>Ordinarily, requests containing a Cache-Control: no-cache or
571 Pragma: no-cache header value will not be served from the cache. The
572 <code class="directive">CacheIgnoreCacheControl</code> directive allows this
573 behavior to be overridden. <code class="directive">CacheIgnoreCacheControl On</code>
574 tells the server to attempt to serve the resource from the cache even
575 if the request contains no-cache header values.</p>
577 <pre class="prettyprint lang-config">CacheIgnoreCacheControl On</pre>
580 <div class="warning"><h3>Warning:</h3>
581 This directive will allow serving from the cache even if the client has
582 requested that the document not be served from the cache. This might
583 result in stale content being served.
588 <li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li>
589 <li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li>
592 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
593 <div class="directive-section"><h2><a name="CacheIgnoreHeaders" id="CacheIgnoreHeaders">CacheIgnoreHeaders</a> <a name="cacheignoreheaders" id="cacheignoreheaders">Directive</a></h2>
594 <table class="directive">
595 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Do not store the given HTTP header(s) in the cache.
597 <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>
598 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreHeaders None</code></td></tr>
599 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
600 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
601 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
603 <p>According to RFC 2616, hop-by-hop HTTP headers are not stored in
604 the cache. The following HTTP headers are hop-by-hop headers and thus
605 do not get stored in the cache in <em>any</em> case regardless of the
606 setting of <code class="directive">CacheIgnoreHeaders</code>:</p>
609 <li><code>Connection</code></li>
610 <li><code>Keep-Alive</code></li>
611 <li><code>Proxy-Authenticate</code></li>
612 <li><code>Proxy-Authorization</code></li>
613 <li><code>TE</code></li>
614 <li><code>Trailers</code></li>
615 <li><code>Transfer-Encoding</code></li>
616 <li><code>Upgrade</code></li>
619 <p><code class="directive">CacheIgnoreHeaders</code> specifies additional HTTP
620 headers that should not to be stored in the cache. For example, it makes
621 sense in some cases to prevent cookies from being stored in the cache.</p>
623 <p><code class="directive">CacheIgnoreHeaders</code> takes a space separated list
624 of HTTP headers that should not be stored in the cache. If only hop-by-hop
625 headers not should be stored in the cache (the RFC 2616 compliant
626 behaviour), <code class="directive">CacheIgnoreHeaders</code> can be set to
627 <code>None</code>.</p>
629 <div class="example"><h3>Example 1</h3><pre class="prettyprint lang-config">CacheIgnoreHeaders Set-Cookie</pre>
632 <div class="example"><h3>Example 2</h3><pre class="prettyprint lang-config">CacheIgnoreHeaders None</pre>
635 <div class="warning"><h3>Warning:</h3>
636 If headers like <code>Expires</code> which are needed for proper cache
637 management are not stored due to a
638 <code class="directive">CacheIgnoreHeaders</code> setting, the behaviour of
639 mod_cache is undefined.
643 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
644 <div class="directive-section"><h2><a name="CacheIgnoreNoLastMod" id="CacheIgnoreNoLastMod">CacheIgnoreNoLastMod</a> <a name="cacheignorenolastmod" id="cacheignorenolastmod">Directive</a></h2>
645 <table class="directive">
646 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore the fact that a response has no Last Modified
648 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreNoLastMod On|Off</code></td></tr>
649 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreNoLastMod Off</code></td></tr>
650 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
651 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
652 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
654 <p>Ordinarily, documents without a last-modified date are not cached.
655 Under some circumstances the last-modified date is removed (during
656 <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> processing for example) or not provided
657 at all. The <code class="directive">CacheIgnoreNoLastMod</code> directive
658 provides a way to specify that documents without last-modified dates
659 should be considered for caching, even without a last-modified date.
660 If neither a last-modified date nor an expiry date are provided with
661 the document then the value specified by the
662 <code class="directive">CacheDefaultExpire</code> directive will be used to
663 generate an expiration date.</p>
665 <pre class="prettyprint lang-config">CacheIgnoreNoLastMod On</pre>
669 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
670 <div class="directive-section"><h2><a name="CacheIgnoreQueryString" id="CacheIgnoreQueryString">CacheIgnoreQueryString</a> <a name="cacheignorequerystring" id="cacheignorequerystring">Directive</a></h2>
671 <table class="directive">
672 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore query string when caching</td></tr>
673 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreQueryString On|Off</code></td></tr>
674 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreQueryString Off</code></td></tr>
675 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
676 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
677 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
679 <p>Ordinarily, requests with query string parameters are cached separately
680 for each unique query string. This is according to RFC 2616/13.9 done only
681 if an expiration time is specified. The
682 <code class="directive">CacheIgnoreQueryString</code> directive tells the cache to
683 cache requests even if no expiration time is specified, and to reply with
684 a cached reply even if the query string differs. From a caching point of
685 view the request is treated as if having no query string when this
686 directive is enabled.</p>
688 <pre class="prettyprint lang-config">CacheIgnoreQueryString On</pre>
693 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
694 <div class="directive-section"><h2><a name="CacheIgnoreURLSessionIdentifiers" id="CacheIgnoreURLSessionIdentifiers">CacheIgnoreURLSessionIdentifiers</a> <a name="cacheignoreurlsessionidentifiers" id="cacheignoreurlsessionidentifiers">Directive</a></h2>
695 <table class="directive">
696 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore defined session identifiers encoded in the URL when caching
698 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreURLSessionIdentifiers <var>identifier</var> [<var>identifier</var>] ...</code></td></tr>
699 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreURLSessionIdentifiers None</code></td></tr>
700 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
701 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
702 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
704 <p>Sometimes applications encode the session identifier into the URL like in the following
708 <li><code>/someapplication/image.gif;jsessionid=123456789</code></li>
709 <li><code>/someapplication/image.gif?PHPSESSIONID=12345678</code></li>
711 <p>This causes cacheable resources to be stored separately for each session, which
712 is often not desired. <code class="directive">CacheIgnoreURLSessionIdentifiers</code> lets
713 define a list of identifiers that are removed from the key that is used to identify
714 an entity in the cache, such that cacheable resources are not stored separately for
717 <p><code>CacheIgnoreURLSessionIdentifiers None</code> clears the list of ignored
718 identifiers. Otherwise, each identifier is added to the list.</p>
720 <div class="example"><h3>Example 1</h3><pre class="prettyprint lang-config">CacheIgnoreURLSessionIdentifiers jsessionid</pre>
723 <div class="example"><h3>Example 2</h3><pre class="prettyprint lang-config">CacheIgnoreURLSessionIdentifiers None</pre>
728 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
729 <div class="directive-section"><h2><a name="CacheKeyBaseURL" id="CacheKeyBaseURL">CacheKeyBaseURL</a> <a name="cachekeybaseurl" id="cachekeybaseurl">Directive</a></h2>
730 <table class="directive">
731 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Override the base URL of reverse proxied cache keys.</td></tr>
732 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheKeyBaseURL <var>URL</var></code></td></tr>
733 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheKeyBaseURL http://example.com</code></td></tr>
734 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
735 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
736 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
737 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr>
739 <p>When the <code class="directive"><a href="#cachekeybaseurl">CacheKeyBaseURL</a></code> directive
740 is specified, the URL provided will be used as the base URL to calculate
741 the URL of the cache keys in the reverse proxy configuration. When not specified,
742 the scheme, hostname and port of the current virtual host is used to construct
743 the cache key. When a cluster of machines is present, and all cached entries
744 should be cached beneath the same cache key, a new base URL can be specified
745 with this directive.</p>
747 <pre class="prettyprint lang-config"># Override the base URL of the cache key.
748 CacheKeyBaseURL http://www.example.com/</pre>
751 <div class="warning">Take care when setting this directive. If two separate virtual
752 hosts are accidentally given the same base URL, entries from one virtual host
753 will be served to the other.</div>
757 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
758 <div class="directive-section"><h2><a name="CacheLastModifiedFactor" id="CacheLastModifiedFactor">CacheLastModifiedFactor</a> <a name="cachelastmodifiedfactor" id="cachelastmodifiedfactor">Directive</a></h2>
759 <table class="directive">
760 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The factor used to compute an expiry date based on the
761 LastModified date.</td></tr>
762 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLastModifiedFactor <var>float</var></code></td></tr>
763 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLastModifiedFactor 0.1</code></td></tr>
764 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
765 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
766 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
768 <p>In the event that a document does not provide an expiry date but does
769 provide a last-modified date, an expiry date can be calculated based on
770 the time since the document was last modified. The
771 <code class="directive">CacheLastModifiedFactor</code> directive specifies a
772 <var>factor</var> to be used in the generation of this expiry date
773 according to the following formula:
775 <code>expiry-period = time-since-last-modified-date * <var>factor</var>
776 expiry-date = current-date + expiry-period</code>
778 For example, if the document was last modified 10 hours ago, and
779 <var>factor</var> is 0.1 then the expiry-period will be set to
780 10*0.1 = 1 hour. If the current time was 3:00pm then the computed
781 expiry-date would be 3:00pm + 1hour = 4:00pm.
783 If the expiry-period would be longer than that set by
784 <code class="directive">CacheMaxExpire</code>, then the latter takes
787 <pre class="prettyprint lang-config">CacheLastModifiedFactor 0.5</pre>
791 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
792 <div class="directive-section"><h2><a name="CacheLock" id="CacheLock">CacheLock</a> <a name="cachelock" id="cachelock">Directive</a></h2>
793 <table class="directive">
794 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable the thundering herd lock.</td></tr>
795 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLock <var>on|off</var></code></td></tr>
796 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLock off</code></td></tr>
797 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
798 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
799 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
801 <p>The <code class="directive">CacheLock</code> directive enables the thundering herd lock
802 for the given URL space.</p>
804 <p>In a minimal configuration the following directive is all that is needed to
805 enable the thundering herd lock in the default run-time file directory.</p>
807 <pre class="prettyprint lang-config"># Enable cache lock
811 <p>Locks consist of empty files that only exist for stale URLs in flight, so this
812 is significantly less resource intensive than the traditional disk cache.</p>
815 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
816 <div class="directive-section"><h2><a name="CacheLockMaxAge" id="CacheLockMaxAge">CacheLockMaxAge</a> <a name="cachelockmaxage" id="cachelockmaxage">Directive</a></h2>
817 <table class="directive">
818 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the maximum possible age of a cache lock.</td></tr>
819 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockMaxAge <var>integer</var></code></td></tr>
820 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockMaxAge 5</code></td></tr>
821 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
822 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
823 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
825 <p>The <code class="directive">CacheLockMaxAge</code> directive specifies the maximum
826 age of any cache lock.</p>
828 <p>A lock older than this value in seconds will be ignored, and the next
829 incoming request will be given the opportunity to re-establish the lock.
830 This mechanism prevents a slow client taking an excessively long time to refresh
835 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
836 <div class="directive-section"><h2><a name="CacheLockPath" id="CacheLockPath">CacheLockPath</a> <a name="cachelockpath" id="cachelockpath">Directive</a></h2>
837 <table class="directive">
838 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the lock path directory.</td></tr>
839 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockPath <var>directory</var></code></td></tr>
840 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockPath mod_cache-lock</code></td></tr>
841 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
842 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
843 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
845 <p>The <code class="directive">CacheLockPath</code> directive allows you to specify the
846 directory in which the locks are created. If <var>directory</var> is not an absolute
847 path, the location specified will be relative to the value of
848 <code class="directive"><a href="../mod/core.html#defaultruntimedir">DefaultRuntimeDir</a></code>.</p>
851 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
852 <div class="directive-section"><h2><a name="CacheMaxExpire" id="CacheMaxExpire">CacheMaxExpire</a> <a name="cachemaxexpire" id="cachemaxexpire">Directive</a></h2>
853 <table class="directive">
854 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum time in seconds to cache a document</td></tr>
855 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMaxExpire <var>seconds</var></code></td></tr>
856 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMaxExpire 86400 (one day)</code></td></tr>
857 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
858 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
859 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
861 <p>The <code class="directive">CacheMaxExpire</code> directive specifies the maximum number of
862 seconds for which cacheable HTTP documents will be retained without checking the origin
863 server. Thus, documents will be out of date at most this number of seconds. This maximum
864 value is enforced even if an expiry date was supplied with the document.</p>
866 <pre class="prettyprint lang-config">CacheMaxExpire 604800</pre>
870 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
871 <div class="directive-section"><h2><a name="CacheMinExpire" id="CacheMinExpire">CacheMinExpire</a> <a name="cacheminexpire" id="cacheminexpire">Directive</a></h2>
872 <table class="directive">
873 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The minimum time in seconds to cache a document</td></tr>
874 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMinExpire <var>seconds</var></code></td></tr>
875 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMinExpire 0</code></td></tr>
876 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
877 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
878 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
880 <p>The <code class="directive">CacheMinExpire</code> directive specifies the minimum number of
881 seconds for which cacheable HTTP documents will be retained without checking the origin
882 server. This is only used if no valid expire time was supplied with the document.</p>
885 <pre class="prettyprint lang-config">CacheMinExpire 3600</pre>
889 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
890 <div class="directive-section"><h2><a name="CacheQuickHandler" id="CacheQuickHandler">CacheQuickHandler</a> <a name="cachequickhandler" id="cachequickhandler">Directive</a></h2>
891 <table class="directive">
892 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Run the cache from the quick handler.</td></tr>
893 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheQuickHandler <var>on|off</var></code></td></tr>
894 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheQuickHandler on</code></td></tr>
895 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
896 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
897 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
898 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Apache HTTP Server 2.3.3 and later</td></tr>
900 <p>The <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code> directive
901 controls the phase in which the cache is handled.</p>
903 <p>In the default enabled configuration, the cache operates within the quick
904 handler phase. This phase short circuits the majority of server processing,
905 and represents the most performant mode of operation for a typical server.
906 The cache <strong>bolts onto</strong> the front of the server, and the
907 majority of server processing is avoided.</p>
909 <p>When disabled, the cache operates as a normal handler, and is subject to
910 the full set of phases when handling a server request. While this mode is
911 slower than the default, it allows the cache to be used in cases where full
912 processing is required, such as when content is subject to authorization.</p>
914 <pre class="prettyprint lang-config"># Run cache as a normal handler
915 CacheQuickHandler off</pre>
918 <p>It is also possible, when the quick handler is disabled, for the
919 administrator to choose the precise location within the filter chain where
920 caching is to be performed, by adding the <strong>CACHE</strong> filter to
923 <pre class="prettyprint lang-config"># Cache content before mod_include and mod_deflate
924 CacheQuickHandler off
925 AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html</pre>
928 <p>If the CACHE filter is specified more than once, the last instance will
933 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
934 <div class="directive-section"><h2><a name="CacheStaleOnError" id="CacheStaleOnError">CacheStaleOnError</a> <a name="cachestaleonerror" id="cachestaleonerror">Directive</a></h2>
935 <table class="directive">
936 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Serve stale content in place of 5xx responses.</td></tr>
937 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStaleOnError <var>on|off</var></code></td></tr>
938 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStaleOnError on</code></td></tr>
939 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
940 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
941 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
942 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr>
944 <p>When the <code class="directive"><a href="#cachestaleonerror">CacheStaleOnError</a></code> directive
945 is switched on, and when stale data is available in the cache, the cache will
946 respond to 5xx responses from the backend by returning the stale data instead of
947 the 5xx response. While the Cache-Control headers sent by clients will be respected,
948 and the raw 5xx responses returned to the client on request, the 5xx response so
949 returned to the client will not invalidate the content in the cache.</p>
951 <pre class="prettyprint lang-config"># Serve stale data on error.
952 CacheStaleOnError on</pre>
957 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
958 <div class="directive-section"><h2><a name="CacheStoreExpired" id="CacheStoreExpired">CacheStoreExpired</a> <a name="cachestoreexpired" id="cachestoreexpired">Directive</a></h2>
959 <table class="directive">
960 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Attempt to cache responses that the server reports as expired</td></tr>
961 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStoreExpired On|Off</code></td></tr>
962 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStoreExpired Off</code></td></tr>
963 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
964 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
965 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
967 <p>Since httpd 2.2.4, responses which have already expired are not
968 stored in the cache. The <code class="directive">CacheStoreExpired</code>
969 directive allows this behavior to be overridden.
970 <code class="directive">CacheStoreExpired</code> On
971 tells the server to attempt to cache the resource if it is stale.
972 Subsequent requests would trigger an If-Modified-Since request of
973 the origin server, and the response may be fulfilled from cache
974 if the backend resource has not changed.</p>
976 <pre class="prettyprint lang-config">CacheStoreExpired On</pre>
980 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
981 <div class="directive-section"><h2><a name="CacheStoreNoStore" id="CacheStoreNoStore">CacheStoreNoStore</a> <a name="cachestorenostore" id="cachestorenostore">Directive</a></h2>
982 <table class="directive">
983 <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>
984 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStoreNoStore On|Off</code></td></tr>
985 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStoreNoStore Off</code></td></tr>
986 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
987 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
988 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
990 <p>Ordinarily, requests or responses with Cache-Control: no-store header
991 values will not be stored in the cache. The
992 <code class="directive">CacheStoreNoStore</code> directive allows this
993 behavior to be overridden. <code class="directive">CacheStoreNoStore</code> On
994 tells the server to attempt to cache the resource even if it contains
995 no-store header values.</p>
997 <pre class="prettyprint lang-config">CacheStoreNoStore On</pre>
1000 <div class="warning"><h3>Warning:</h3>
1001 As described in RFC 2616, the no-store directive is intended to
1002 "prevent the inadvertent release or retention of sensitive information
1003 (for example, on backup tapes)." Enabling this option could store
1004 sensitive information in the cache. You are hereby warned.
1009 <li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li>
1010 <li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li>
1013 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
1014 <div class="directive-section"><h2><a name="CacheStorePrivate" id="CacheStorePrivate">CacheStorePrivate</a> <a name="cachestoreprivate" id="cachestoreprivate">Directive</a></h2>
1015 <table class="directive">
1016 <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>
1017 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStorePrivate On|Off</code></td></tr>
1018 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStorePrivate Off</code></td></tr>
1019 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
1020 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
1021 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
1023 <p>Ordinarily, responses with Cache-Control: private header values will not
1024 be stored in the cache. The <code class="directive">CacheStorePrivate</code>
1025 directive allows this behavior to be overridden.
1026 <code class="directive">CacheStorePrivate</code> On
1027 tells the server to attempt to cache the resource even if it contains
1028 private header values.</p>
1030 <pre class="prettyprint lang-config">CacheStorePrivate On</pre>
1033 <div class="warning"><h3>Warning:</h3>
1034 This directive will allow caching even if the upstream server has
1035 requested that the resource not be cached. This directive is only
1036 ideal for a 'private' cache.
1041 <li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li>
1042 <li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li>
1046 <div class="bottomlang">
1047 <p><span>Available Languages: </span><a href="../en/mod/mod_cache.html" title="English"> en </a> |
1048 <a href="../fr/mod/mod_cache.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
1049 <a href="../ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
1050 <a href="../ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
1051 </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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