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16 <p class="apache">Apache HTTP Server Version 2.3</p>
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21 <div id="page-content">
22 <div id="preamble"><h1>Apache Module mod_cache</h1>
24 <p><span>Available Languages: </span><a href="../en/mod/mod_cache.html" title="English"> en </a> |
25 <a href="../fr/mod/mod_cache.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
26 <a href="../ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
27 <a href="../ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
29 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Content cache keyed to URIs.</td></tr>
30 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
31 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>cache_module</td></tr>
32 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_cache.c</td></tr></table>
35 <div class="warning">This module should be used with care, as when the
36 <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code> directive is
37 in its default value of <strong>on</strong>, the <code class="directive"><a href="../mod/mod_authz_host.html#allow">Allow</a></code> and <code class="directive"><a href="../mod/mod_authz_host.html#deny">Deny</a></code> directives will be circumvented.
38 You should not enable quick handler caching for any content to which you
39 wish to limit access by client host name, address or environment
42 <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 HTTP
43 content cache that can be used to cache either local or proxied content.
44 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> requires the services of one or more storage
45 management modules. One storage management module is included in
46 the base Apache distribution:</p>
48 <dt><code class="module"><a href="../mod/mod_disk_cache.html">mod_disk_cache</a></code></dt>
49 <dd>implements a disk based storage manager.</dd>
52 <p>Content is stored in and retrieved from the cache using URI based keys. Content with
53 access protection is not cached.</p>
54 <p>Further details, discussion, and examples, are provided in the
55 <a href="../caching.html">Caching Guide</a>.</p>
57 <div id="quickview"><h3 class="directives">Directives</h3>
59 <li><img alt="" src="../images/down.gif" /> <a href="#cachedefaultexpire">CacheDefaultExpire</a></li>
60 <li><img alt="" src="../images/down.gif" /> <a href="#cachedisable">CacheDisable</a></li>
61 <li><img alt="" src="../images/down.gif" /> <a href="#cacheenable">CacheEnable</a></li>
62 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></li>
63 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignoreheaders">CacheIgnoreHeaders</a></li>
64 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignorenolastmod">CacheIgnoreNoLastMod</a></li>
65 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignorequerystring">CacheIgnoreQueryString</a></li>
66 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignoreurlsessionidentifiers">CacheIgnoreURLSessionIdentifiers</a></li>
67 <li><img alt="" src="../images/down.gif" /> <a href="#cachelastmodifiedfactor">CacheLastModifiedFactor</a></li>
68 <li><img alt="" src="../images/down.gif" /> <a href="#cachelock">CacheLock</a></li>
69 <li><img alt="" src="../images/down.gif" /> <a href="#cachelockmaxage">CacheLockMaxAge</a></li>
70 <li><img alt="" src="../images/down.gif" /> <a href="#cachelockpath">CacheLockPath</a></li>
71 <li><img alt="" src="../images/down.gif" /> <a href="#cachemaxexpire">CacheMaxExpire</a></li>
72 <li><img alt="" src="../images/down.gif" /> <a href="#cacheminexpire">CacheMinExpire</a></li>
73 <li><img alt="" src="../images/down.gif" /> <a href="#cachequickhandler">CacheQuickHandler</a></li>
74 <li><img alt="" src="../images/down.gif" /> <a href="#cachestoreexpired">CacheStoreExpired</a></li>
75 <li><img alt="" src="../images/down.gif" /> <a href="#cachestorenostore">CacheStoreNoStore</a></li>
76 <li><img alt="" src="../images/down.gif" /> <a href="#cachestoreprivate">CacheStorePrivate</a></li>
80 <li><img alt="" src="../images/down.gif" /> <a href="#related">Related Modules and Directives</a></li>
81 <li><img alt="" src="../images/down.gif" /> <a href="#sampleconf">Sample Configuration</a></li>
82 <li><img alt="" src="../images/down.gif" /> <a href="#thunderingherd">Avoiding the Thundering Herd</a></li>
83 <li><img alt="" src="../images/down.gif" /> <a href="#finecontrol">Fine Control with the CACHE Filter</a></li>
84 </ul><h3>See also</h3>
86 <li><a href="../caching.html">Caching Guide</a></li>
88 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
90 <h2><a name="related" id="related">Related Modules and Directives</a></h2>
91 <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="../mod/mod_disk_cache.html">mod_disk_cache</a></code></li></ul></td><td><ul><li><code class="directive"><a href="../mod/mod_disk_cache.html#cacheroot">CacheRoot</a></code></li><li><code class="directive"><a href="../mod/mod_disk_cache.html#cachedirlevels">CacheDirLevels</a></code></li><li><code class="directive"><a href="../mod/mod_disk_cache.html#cachedirlength">CacheDirLength</a></code></li><li><code class="directive"><a href="../mod/mod_disk_cache.html#cacheminfilesize">CacheMinFileSize</a></code></li><li><code class="directive"><a href="../mod/mod_disk_cache.html#cachemaxfilesize">CacheMaxFileSize</a></code></li></ul></td></tr></table>
92 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
94 <h2><a name="sampleconf" id="sampleconf">Sample Configuration</a></h2>
95 <div class="example"><h3>Sample httpd.conf</h3><p><code>
97 # Sample Cache Configuration<br />
99 LoadModule cache_module modules/mod_cache.so<br />
101 <IfModule mod_cache.c><br />
102 <span class="indent">
103 LoadModule disk_cache_module modules/mod_disk_cache.so<br />
104 <IfModule mod_disk_cache.c><br />
105 <span class="indent">
106 CacheRoot c:/cacheroot<br />
107 CacheEnable disk /<br />
108 CacheDirLevels 5<br />
109 CacheDirLength 3<br />
111 </IfModule> <br />
113 # When acting as a proxy, don't cache the list of security updates<br />
114 CacheDisable http://security.update.server/update-list/<br />
118 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
119 <div class="section">
120 <h2><a name="thunderingherd" id="thunderingherd">Avoiding the Thundering Herd</a></h2>
121 <p>When a cached entry becomes stale, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> will submit
122 a conditional request to the backend, which is expected to confirm whether the
123 cached entry is still fresh, and send an updated entity if not.</p>
124 <p>A small but finite amount of time exists between the time the cached entity
125 becomes stale, and the time the stale entity is fully refreshed. On a busy
126 server, a significant number of requests might arrive during this time, and
127 cause a <strong>thundering herd</strong> of requests to strike the backend
128 suddenly and unpredicably.</p>
129 <p>To keep the thundering herd at bay, the <code class="directive">CacheLock</code>
130 directive can be used to define a directory in which locks are created for
131 URLs <strong>in flight</strong>. The lock is used as a <strong>hint</strong>
132 by other requests to either suppress an attempt to cache (someone else has
133 gone to fetch the entity), or to indicate that a stale entry is being refreshed
134 (stale content will be returned in the mean time).
136 <h3>Initial caching of an entry</h3>
138 <p>When an entity is cached for the first time, a lock will be created for the
139 entity until the response has been fully cached. During the lifetime of the
140 lock, the cache will suppress the second and subsequent attempt to cache the
141 same entity. While this doesn't hold back the thundering herd, it does stop
142 the cache attempting to cache the same entity multiple times simultaneously.
145 <h3>Refreshment of a stale entry</h3>
147 <p>When an entity reaches its freshness lifetime and becomes stale, a lock
148 will be created for the entity until the response has either been confirmed as
149 still fresh, or replaced by the backend. During the lifetime of the lock, the
150 second and subsequent incoming request will cause stale data to be returned,
151 and the thundering herd is kept at bay.</p>
153 <h3>Locks and Cache-Control: no-cache</h3>
155 <p>Locks are used as a <strong>hint only</strong> to enable the cache to be
156 more gentle on backend servers, however the lock can be overridden if necessary.
157 If the client sends a request with a Cache-Control header forcing a reload, any
158 lock that may be present will be ignored, and the client's request will be
159 honoured immediately and the cached entry refreshed.</p>
160 <p>As a further safety mechanism, locks have a configurable maximum age.
161 Once this age has been reached, the lock is removed, and a new request is
162 given the opportunity to create a new lock. This maximum age can be set using
163 the <code class="directive">CacheLockMaxAge</code> directive, and defaults to 5
167 <h3>Example configuration</h3>
169 <div class="example"><h3>Enabling the cache lock</h3><p><code>
171 # Enable the cache lock<br />
173 <IfModule mod_cache.c><br />
174 <span class="indent">
176 CacheLockPath /tmp/mod_cache-lock<br />
177 CacheLockMaxAge 5<br />
182 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
183 <div class="section">
184 <h2><a name="finecontrol" id="finecontrol">Fine Control with the CACHE Filter</a></h2>
185 <p>Under the default mode of cache operation, the cache runs as a quick handler,
186 short circuiting the majority of server processing and offering the highest
187 cache performance available.</p>
189 <p>In this mode, the cache <strong>bolts onto</strong> the front of the server,
190 acting as if a free standing RFC2616 caching proxy had been placed in front of
193 <p>While this mode offers the best performance, the administrator may find that
194 under certain circumstances they may want to perform further processing on the
195 request after the request is cached, such as to inject personalisation into the
196 cached page, or to apply authorisation restrictions to the content. Under these
197 circumstances, an administrator is often forced to place independent reverse
198 proxy servers either behind or in front of the caching server to achieve this.</p>
200 <p>To solve this problem the <code class="directive"><a href="#cachequickhandler ">CacheQuickHandler
201 </a></code> directive can be set to <strong>off</strong>, and the server will
202 process all phases normally handled by a non-cached request, including the
203 <strong>authentication and authorisation</strong> phases.</p>
205 <p>In addition, the administrator may optionally specify the <strong>precise point
206 within the filter chain</strong> where caching is to take place by adding the
207 <strong>CACHE</strong> filter to the output filter chain.</p>
209 <p>For example, to cache content before applying compression to the response,
210 place the <strong>CACHE</strong> filter before the <strong>DEFLATE</strong>
211 filter as in the example below:</p>
213 <div class="example"><p><code>
214 # Cache content before optional compression<br />
215 CacheQuickHandler off<br />
216 AddOutputFilterByType CACHE;DEFLATE text/plain<br /><br />
219 <p>Another option is to have content cached before personalisation is applied
220 by <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> (or another content processing filter). In this
221 example templates containing tags understood by
222 <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> are cached before being parsed:</p>
224 <div class="example"><p><code>
225 # Cache content before mod_include and mod_deflate<br />
226 CacheQuickHandler off<br />
227 AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html<br /><br />
230 <p>You may place the <strong>CACHE</strong> filter anywhere you wish within the
231 filter chain. In this example, content is cached after being parsed by
232 <code class="module"><a href="../mod/mod_include.html">mod_include</a></code>, but before being processed by
233 <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code>:</p>
235 <div class="example"><p><code>
236 # Cache content between mod_include and mod_deflate<br />
237 CacheQuickHandler off<br />
238 AddOutputFilterByType INCLUDES;CACHE;DEFLATE text/html<br /><br />
241 <div class="warning"><h3>Warning:</h3>If the location of the
242 <strong>CACHE</strong> filter in the filter chain is changed for any reason,
243 you may need to <strong>flush your cache</strong> to ensure that your data
244 served remains consistent. <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> is not in a position
245 to enforce this for you.</div>
248 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
249 <div class="directive-section"><h2><a name="CacheDefaultExpire" id="CacheDefaultExpire">CacheDefaultExpire</a> <a name="cachedefaultexpire" id="cachedefaultexpire">Directive</a></h2>
250 <table class="directive">
251 <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>
252 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDefaultExpire <var>seconds</var></code></td></tr>
253 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheDefaultExpire 3600 (one hour)</code></td></tr>
254 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
255 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
256 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
258 <p>The <code class="directive">CacheDefaultExpire</code> directive specifies a default time,
259 in seconds, to cache a document if neither an expiry date nor last-modified date are provided
260 with the document. The value specified with the <code class="directive">CacheMaxExpire</code>
261 directive does <em>not</em> override this setting.</p>
263 <div class="example"><p><code>
264 CacheDefaultExpire 86400
268 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
269 <div class="directive-section"><h2><a name="CacheDisable" id="CacheDisable">CacheDisable</a> <a name="cachedisable" id="cachedisable">Directive</a></h2>
270 <table class="directive">
271 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Disable caching of specified URLs</td></tr>
272 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDisable <var>url-string</var> | <var>on</var></code></td></tr>
273 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
274 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
275 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
277 <p>The <code class="directive">CacheDisable</code> directive instructs
278 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to <em>not</em> cache urls at or below
279 <var>url-string</var>.</p>
281 <div class="example"><h3>Example</h3><p><code>
282 CacheDisable /local_files
285 <p>If used in a <code class="directive"><Location></code> directive,
286 the path needs to be specified below the Location, or if the word "on"
287 is used, caching for the whole location will be disabled.</p>
289 <div class="example"><h3>Example</h3><p><code>
290 <Location /foo><br />
291 CacheDisable on<br />
292 </Location><br />
295 <p> The <code>no-cache</code> environment variable can be set to
296 disable caching on a finer grained set of resources in versions
297 2.2.12 and later.</p>
302 <li><a href="../env.html">Environment Variables in Apache</a></li>
305 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
306 <div class="directive-section"><h2><a name="CacheEnable" id="CacheEnable">CacheEnable</a> <a name="cacheenable" id="cacheenable">Directive</a></h2>
307 <table class="directive">
308 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable caching of specified URLs using a specified storage
310 <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>
311 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
312 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
313 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
315 <p>The <code class="directive">CacheEnable</code> directive instructs
316 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to cache urls at or below
317 <var>url-string</var>. The cache storage manager is specified with the
318 <var>cache_type</var> argument. If the <code class="directive">CacheEnable</code>
319 directive is placed inside a <code class="directive"><Location></code>
320 directive, the <var>url-string</var> becomes optional.
321 <var>cache_type</var> <code>disk</code> instructs
322 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the disk based storage manager
323 implemented by <code class="module"><a href="../mod/mod_disk_cache.html">mod_disk_cache</a></code>.</p>
324 <p>In the event that the URL space overlaps between different
325 <code class="directive">CacheEnable</code> directives (as in the example below),
326 each possible storage manager will be run until the first one that
327 actually processes the request. The order in which the storage managers are
328 run is determined by the order of the <code class="directive">CacheEnable</code>
329 directives in the configuration file.</p>
331 <p>When acting as a forward proxy server, <var>url-string</var> can
332 also be used to specify remote sites and proxy protocols which
333 caching should be enabled for.</p>
335 <div class="example"><p><code>
336 # Cache proxied url's<br />
337 CacheEnable disk /<br /><br />
338 # Cache FTP-proxied url's<br />
339 CacheEnable disk ftp://<br /><br />
340 # Cache content from www.apache.org<br />
341 CacheEnable disk http://www.apache.org/<br />
344 <p>A hostname starting with a <strong>"*"</strong> matches all hostnames with
345 that suffix. A hostname starting with <strong>"."</strong> matches all
346 hostnames containing the domain components that follow.</p>
348 <div class="example"><p><code>
349 # Match www.apache.org, and fooapache.org<br />
350 CacheEnable disk http://*apache.org/<br />
351 # Match www.apache.org, but not fooapache.org<br />
352 CacheEnable disk http://.apache.org/<br />
355 <p> The <code>no-cache</code> environment variable can be set to
356 disable caching on a finer grained set of resources in versions
357 2.2.12 and later.</p>
362 <li><a href="../env.html">Environment Variables in Apache</a></li>
365 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
366 <div class="directive-section"><h2><a name="CacheIgnoreCacheControl" id="CacheIgnoreCacheControl">CacheIgnoreCacheControl</a> <a name="cacheignorecachecontrol" id="cacheignorecachecontrol">Directive</a></h2>
367 <table class="directive">
368 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore request to not serve cached content to client</td></tr>
369 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreCacheControl On|Off</code></td></tr>
370 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreCacheControl Off</code></td></tr>
371 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
372 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
373 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
375 <p>Ordinarily, requests containing a Cache-Control: no-cache or
376 Pragma: no-cache header value will not be served from the cache. The
377 <code class="directive">CacheIgnoreCacheControl</code> directive allows this
378 behavior to be overridden. <code class="directive">CacheIgnoreCacheControl On</code>
379 tells the server to attempt to serve the resource from the cache even
380 if the request contains no-cache header values. Resources requiring
381 authorization will <em>never</em> be cached.</p>
383 <div class="example"><p><code>
384 CacheIgnoreCacheControl On
387 <div class="warning"><h3>Warning:</h3>
388 This directive will allow serving from the cache even if the client has
389 requested that the document not be served from the cache. This might
390 result in stale content being served.
395 <li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li>
396 <li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li>
399 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
400 <div class="directive-section"><h2><a name="CacheIgnoreHeaders" id="CacheIgnoreHeaders">CacheIgnoreHeaders</a> <a name="cacheignoreheaders" id="cacheignoreheaders">Directive</a></h2>
401 <table class="directive">
402 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Do not store the given HTTP header(s) in the cache.
404 <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>
405 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreHeaders None</code></td></tr>
406 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
407 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
408 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
410 <p>According to RFC 2616, hop-by-hop HTTP headers are not stored in
411 the cache. The following HTTP headers are hop-by-hop headers and thus
412 do not get stored in the cache in <em>any</em> case regardless of the
413 setting of <code class="directive">CacheIgnoreHeaders</code>:</p>
416 <li><code>Connection</code></li>
417 <li><code>Keep-Alive</code></li>
418 <li><code>Proxy-Authenticate</code></li>
419 <li><code>Proxy-Authorization</code></li>
420 <li><code>TE</code></li>
421 <li><code>Trailers</code></li>
422 <li><code>Transfer-Encoding</code></li>
423 <li><code>Upgrade</code></li>
426 <p><code class="directive">CacheIgnoreHeaders</code> specifies additional HTTP
427 headers that should not to be stored in the cache. For example, it makes
428 sense in some cases to prevent cookies from being stored in the cache.</p>
430 <p><code class="directive">CacheIgnoreHeaders</code> takes a space separated list
431 of HTTP headers that should not be stored in the cache. If only hop-by-hop
432 headers not should be stored in the cache (the RFC 2616 compliant
433 behaviour), <code class="directive">CacheIgnoreHeaders</code> can be set to
434 <code>None</code>.</p>
436 <div class="example"><h3>Example 1</h3><p><code>
437 CacheIgnoreHeaders Set-Cookie
440 <div class="example"><h3>Example 2</h3><p><code>
441 CacheIgnoreHeaders None
444 <div class="warning"><h3>Warning:</h3>
445 If headers like <code>Expires</code> which are needed for proper cache
446 management are not stored due to a
447 <code class="directive">CacheIgnoreHeaders</code> setting, the behaviour of
448 mod_cache is undefined.
452 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
453 <div class="directive-section"><h2><a name="CacheIgnoreNoLastMod" id="CacheIgnoreNoLastMod">CacheIgnoreNoLastMod</a> <a name="cacheignorenolastmod" id="cacheignorenolastmod">Directive</a></h2>
454 <table class="directive">
455 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore the fact that a response has no Last Modified
457 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreNoLastMod On|Off</code></td></tr>
458 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreNoLastMod Off</code></td></tr>
459 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
460 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
461 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
463 <p>Ordinarily, documents without a last-modified date are not cached.
464 Under some circumstances the last-modified date is removed (during
465 <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> processing for example) or not provided
466 at all. The <code class="directive">CacheIgnoreNoLastMod</code> directive
467 provides a way to specify that documents without last-modified dates
468 should be considered for caching, even without a last-modified date.
469 If neither a last-modified date nor an expiry date are provided with
470 the document then the value specified by the
471 <code class="directive">CacheDefaultExpire</code> directive will be used to
472 generate an expiration date.</p>
474 <div class="example"><p><code>
475 CacheIgnoreNoLastMod On
479 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
480 <div class="directive-section"><h2><a name="CacheIgnoreQueryString" id="CacheIgnoreQueryString">CacheIgnoreQueryString</a> <a name="cacheignorequerystring" id="cacheignorequerystring">Directive</a></h2>
481 <table class="directive">
482 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore query string when caching</td></tr>
483 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreQueryString On|Off</code></td></tr>
484 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreQueryString Off</code></td></tr>
485 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
486 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
487 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
489 <p>Ordinarily, requests with query string parameters are cached separately
490 for each unique query string. This is according to RFC 2616/13.9 done only
491 if an expiration time is specified. The
492 <code class="directive">CacheIgnoreQueryString</code> directive tells the cache to
493 cache requests even if no expiration time is specified, and to reply with
494 a cached reply even if the query string differs. From a caching point of
495 view the request is treated as if having no query string when this
496 directive is enabled.</p>
498 <div class="example"><p><code>
499 CacheIgnoreQueryString On
504 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
505 <div class="directive-section"><h2><a name="CacheIgnoreURLSessionIdentifiers" id="CacheIgnoreURLSessionIdentifiers">CacheIgnoreURLSessionIdentifiers</a> <a name="cacheignoreurlsessionidentifiers" id="cacheignoreurlsessionidentifiers">Directive</a></h2>
506 <table class="directive">
507 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore defined session identifiers encoded in the URL when caching
509 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreURLSessionIdentifiers <var>identifier</var> [<var>identifier</var>] ...</code></td></tr>
510 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreURLSessionIdentifiers None</code></td></tr>
511 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
512 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
513 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
515 <p>Sometimes applications encode the session identifier into the URL like in the following
519 <li><code>/someapplication/image.gif;jsessionid=123456789</code></li>
520 <li><code>/someapplication/image.gif?PHPSESSIONID=12345678</code></li>
522 <p>This causes cachable resources to be stored separately for each session, which
523 is often not desired. <code class="directive">CacheIgnoreURLSessionIdentifiers</code> lets
524 define a list of identifiers that are removed from the key that is used to identify
525 an entity in the cache, such that cachable resources are not stored separately for
528 <p><code>CacheIgnoreURLSessionIdentifiers None</code> clears the list of ignored
529 identifiers. Otherwise, each identifier is added to the list.</p>
531 <div class="example"><h3>Example 1</h3><p><code>
532 CacheIgnoreURLSessionIdentifiers jsessionid
535 <div class="example"><h3>Example 2</h3><p><code>
536 CacheIgnoreURLSessionIdentifiers None
541 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
542 <div class="directive-section"><h2><a name="CacheLastModifiedFactor" id="CacheLastModifiedFactor">CacheLastModifiedFactor</a> <a name="cachelastmodifiedfactor" id="cachelastmodifiedfactor">Directive</a></h2>
543 <table class="directive">
544 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The factor used to compute an expiry date based on the
545 LastModified date.</td></tr>
546 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLastModifiedFactor <var>float</var></code></td></tr>
547 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLastModifiedFactor 0.1</code></td></tr>
548 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
549 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
550 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
552 <p>In the event that a document does not provide an expiry date but does
553 provide a last-modified date, an expiry date can be calculated based on
554 the time since the document was last modified. The
555 <code class="directive">CacheLastModifiedFactor</code> directive specifies a
556 <var>factor</var> to be used in the generation of this expiry date
557 according to the following formula:
559 <code>expiry-period = time-since-last-modified-date * <var>factor</var>
560 expiry-date = current-date + expiry-period</code>
562 For example, if the document was last modified 10 hours ago, and
563 <var>factor</var> is 0.1 then the expiry-period will be set to
564 10*0.1 = 1 hour. If the current time was 3:00pm then the computed
565 expiry-date would be 3:00pm + 1hour = 4:00pm.
567 If the expiry-period would be longer than that set by
568 <code class="directive">CacheMaxExpire</code>, then the latter takes
571 <div class="example"><p><code>
572 CacheLastModifiedFactor 0.5
576 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
577 <div class="directive-section"><h2><a name="CacheLock" id="CacheLock">CacheLock</a> <a name="cachelock" id="cachelock">Directive</a></h2>
578 <table class="directive">
579 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable the thundering herd lock.</td></tr>
580 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLock <var>on|off</var></code></td></tr>
581 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLock off</code></td></tr>
582 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
583 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
584 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
585 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.2.15 and later</td></tr>
587 <p>The <code class="directive">CacheLock</code> directive enables the thundering herd lock
588 for the given URL space.</p>
590 <p>In a minimal configuration the following directive is all that is needed to
591 enable the thundering herd lock in the default system temp directory.</p>
593 <div class="example"><p><code>
594 # Enable cache lock<br />
595 CacheLock on<br /><br />
600 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
601 <div class="directive-section"><h2><a name="CacheLockMaxAge" id="CacheLockMaxAge">CacheLockMaxAge</a> <a name="cachelockmaxage" id="cachelockmaxage">Directive</a></h2>
602 <table class="directive">
603 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the maximum possible age of a cache lock.</td></tr>
604 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockMaxAge <var>integer</var></code></td></tr>
605 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockMaxAge 5</code></td></tr>
606 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
607 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
608 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
610 <p>The <code class="directive">CacheLockMaxAge</code> directive specifies the maximum
611 age of any cache lock.</p>
613 <p>A lock older than this value in seconds will be ignored, and the next
614 incoming request will be given the opportunity to re-establish the lock.
615 This mechanism prevents a slow client taking an excessively long time to refresh
620 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
621 <div class="directive-section"><h2><a name="CacheLockPath" id="CacheLockPath">CacheLockPath</a> <a name="cachelockpath" id="cachelockpath">Directive</a></h2>
622 <table class="directive">
623 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the lock path directory.</td></tr>
624 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockPath <var>directory</var></code></td></tr>
625 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockPath /tmp/mod_cache-lock</code></td></tr>
626 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
627 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
628 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
630 <p>The <code class="directive">CacheLockPath</code> directive allows you to specify the
631 directory in which the locks are created. By default, the system's temporary
632 folder is used. Locks consist of empty files that only exist for stale URLs
633 in flight, so is significantly less resource intensive than the traditional
638 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
639 <div class="directive-section"><h2><a name="CacheMaxExpire" id="CacheMaxExpire">CacheMaxExpire</a> <a name="cachemaxexpire" id="cachemaxexpire">Directive</a></h2>
640 <table class="directive">
641 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum time in seconds to cache a document</td></tr>
642 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMaxExpire <var>seconds</var></code></td></tr>
643 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMaxExpire 86400 (one day)</code></td></tr>
644 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
645 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
646 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
648 <p>The <code class="directive">CacheMaxExpire</code> directive specifies the maximum number of
649 seconds for which cachable HTTP documents will be retained without checking the origin
650 server. Thus, documents will be out of date at most this number of seconds. This maximum
651 value is enforced even if an expiry date was supplied with the document.</p>
653 <div class="example"><p><code>
654 CacheMaxExpire 604800
658 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
659 <div class="directive-section"><h2><a name="CacheMinExpire" id="CacheMinExpire">CacheMinExpire</a> <a name="cacheminexpire" id="cacheminexpire">Directive</a></h2>
660 <table class="directive">
661 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The minimum time in seconds to cache a document</td></tr>
662 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMinExpire <var>seconds</var></code></td></tr>
663 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMinExpire 0</code></td></tr>
664 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
665 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
666 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
668 <p>The <code class="directive">CacheMinExpire</code> directive specifies the minimum number of
669 seconds for which cachable HTTP documents will be retained without checking the origin
670 server. This is only used if no valid expire time was supplied with the document.</p>
673 <div class="example"><p><code>
678 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
679 <div class="directive-section"><h2><a name="CacheQuickHandler" id="CacheQuickHandler">CacheQuickHandler</a> <a name="cachequickhandler" id="cachequickhandler">Directive</a></h2>
680 <table class="directive">
681 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Run the cache from the quick handler.</td></tr>
682 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheQuickHandler <var>on|off</var></code></td></tr>
683 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheQuickHandler on</code></td></tr>
684 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
685 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
686 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
688 <p>The <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code> directive
689 controls the phase in which the cache is handled.</p>
691 <p>In the default enabled configuration, the cache operates within the quick
692 handler phase. This phase short circuits the majority of server processing,
693 and represents the most performant mode of operation for a typical server.
694 The cache <strong>bolts onto</strong> the front of the server, and the
695 majority of server processing is avoided.</p>
697 <p>When disabled, the cache operates as a normal handler, and is subject to
698 the full set of phases when handling a server request. While this mode is
699 slower than the default, it allows the cache to be used in cases where full
700 processing is required, such as when content is subject to authorisation.</p>
702 <div class="example"><p><code>
703 # Run cache as a normal handler<br />
704 CacheQuickHandler off<br /><br />
707 <p>It is also possible, when the quick handler is disabled, for the
708 administrator to choose the precise location within the filter chain where
709 caching is to be performed, by adding the <strong>CACHE</strong> filter to
712 <div class="example"><p><code>
713 # Cache content before mod_include and mod_deflate<br />
714 CacheQuickHandler off<br />
715 AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html<br /><br />
718 <p>If the CACHE filter is specified more than once, the last instance will
723 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
724 <div class="directive-section"><h2><a name="CacheStoreExpired" id="CacheStoreExpired">CacheStoreExpired</a> <a name="cachestoreexpired" id="cachestoreexpired">Directive</a></h2>
725 <table class="directive">
726 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Attempt to cache responses that the server reports as expired</td></tr>
727 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStoreExpired On|Off</code></td></tr>
728 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStoreExpired Off</code></td></tr>
729 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
730 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
731 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
733 <p>Since httpd 2.2.4, responses which are already-expired are not
734 stored in the cache. The <code class="directive">CacheStoreExpired</code>
735 directive allows this behavior to be overridden.
736 <code class="directive">CacheStoreExpired</code> On
737 tells the server to attempt to cache the resource if it is stale.
738 Subsequent requests would trigger an If-Modified-Since request of
739 the origin server, and the response may be fulfilled from cache
740 if the backend resource has not changed.</p>
742 <div class="example"><p><code>
747 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
748 <div class="directive-section"><h2><a name="CacheStoreNoStore" id="CacheStoreNoStore">CacheStoreNoStore</a> <a name="cachestorenostore" id="cachestorenostore">Directive</a></h2>
749 <table class="directive">
750 <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>
751 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStoreNoStore On|Off</code></td></tr>
752 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStoreNoStore Off</code></td></tr>
753 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
754 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
755 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
757 <p>Ordinarily, requests or responses with Cache-Control: no-store header
758 values will not be stored in the cache. The
759 <code class="directive">CacheStoreNoCache</code> directive allows this
760 behavior to be overridden. <code class="directive">CacheStoreNoCache</code> On
761 tells the server to attempt to cache the resource even if it contains
762 no-store header values. Resources requiring authorization will
763 <em>never</em> be cached.</p>
765 <div class="example"><p><code>
769 <div class="warning"><h3>Warning:</h3>
770 As described in RFC 2616, the no-store directive is intended to
771 "prevent the inadvertent release or retention of sensitive information
772 (for example, on backup tapes)." Enabling this option could store
773 sensitive information in the cache. You are hereby warned.
778 <li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li>
779 <li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li>
782 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
783 <div class="directive-section"><h2><a name="CacheStorePrivate" id="CacheStorePrivate">CacheStorePrivate</a> <a name="cachestoreprivate" id="cachestoreprivate">Directive</a></h2>
784 <table class="directive">
785 <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>
786 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStorePrivate On|Off</code></td></tr>
787 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStorePrivate Off</code></td></tr>
788 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
789 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
790 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
792 <p>Ordinarily, responses with Cache-Control: private header values will not
793 be stored in the cache. The <code class="directive">CacheStorePrivate</code>
794 directive allows this behavior to be overridden.
795 <code class="directive">CacheStorePrivate</code> On
796 tells the server to attempt to cache the resource even if it contains
797 private header values. Resources requiring authorization will
798 <em>never</em> be cached.</p>
800 <div class="example"><p><code>
804 <div class="warning"><h3>Warning:</h3>
805 This directive will allow caching even if the upstream server has
806 requested that the resource not be cached. This directive is only
807 ideal for a 'private' cache.
812 <li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li>
813 <li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li>
817 <div class="bottomlang">
818 <p><span>Available Languages: </span><a href="../en/mod/mod_cache.html" title="English"> en </a> |
819 <a href="../fr/mod/mod_cache.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
820 <a href="../ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
821 <a href="../ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
822 </div><div id="footer">
823 <p class="apache">Copyright 2010 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
824 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>