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24<div id="page-content">
25<div id="preamble"><h1>Apache Module mod_cache</h1>
26<div class="toplang">
27<p><span>Available Languages: </span><a href="/en/mod/mod_cache.html" title="English">&nbsp;en&nbsp;</a> |
28<a href="/ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
29<a href="/ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a></p>
30</div>
31<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Content cache keyed to URIs.</td></tr>
32<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
33<tr><th><a href="module-dict.html#ModuleIdentifier">Module�Identifier:</a></th><td>cache_module</td></tr>
34<tr><th><a href="module-dict.html#SourceFile">Source�File:</a></th><td>mod_cache.c</td></tr></table>
35<h3>Summary</h3>
36
37    <div class="warning">This module should be used with care and
38    can be used to circumvent <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. You 
39    should not enable caching for any content to which you wish
40    to limit access by client host name, address or environment
41    variable.</div>  
42
43    <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
44    content cache that can be used to cache either local or proxied content.
45    <code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> requires the services of one or more storage
46    management modules. Two storage management modules are included in
47    the base Apache distribution:</p>
48    <dl>
49    <dt><code class="module"><a href="/mod/mod_disk_cache.html">mod_disk_cache</a></code></dt>
50    <dd>implements a disk based storage manager.</dd>
51
52    <dt><code class="module"><a href="/mod/mod_mem_cache.html">mod_mem_cache</a></code></dt>
53    <dd>implements a memory based storage manager. 
54    <code class="module"><a href="/mod/mod_mem_cache.html">mod_mem_cache</a></code> can be configured to operate in two
55    modes: caching open file descriptors or caching objects in heap storage.
56    <code class="module"><a href="/mod/mod_mem_cache.html">mod_mem_cache</a></code> can be used to cache locally generated content
57    or to cache backend server content for <code class="module"><a href="/mod/mod_proxy.html">mod_proxy</a></code> when
58    configured using <code class="directive"><a href="/mod/mod_proxy.html#proxypass">ProxyPass</a></code>
59    (aka <dfn>reverse proxy</dfn>)</dd>
60    </dl>
61
62    <p>Content is stored in and retrieved from the cache using URI based keys. Content with
63    access protection is not cached.</p>
64    <p>Further details, discussion, and examples, are provided in the
65    <a href="/caching.html">Caching Guide</a>.</p>
66</div>
67<div id="quickview"><h3 class="directives">Directives</h3>
68<ul id="toc">
69<li><img alt="" src="/images/down.gif" /> <a href="#cachedefaultexpire">CacheDefaultExpire</a></li>
70<li><img alt="" src="/images/down.gif" /> <a href="#cachedisable">CacheDisable</a></li>
71<li><img alt="" src="/images/down.gif" /> <a href="#cacheenable">CacheEnable</a></li>
72<li><img alt="" src="/images/down.gif" /> <a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></li>
73<li><img alt="" src="/images/down.gif" /> <a href="#cacheignoreheaders">CacheIgnoreHeaders</a></li>
74<li><img alt="" src="/images/down.gif" /> <a href="#cacheignorenolastmod">CacheIgnoreNoLastMod</a></li>
75<li><img alt="" src="/images/down.gif" /> <a href="#cacheignorequerystring">CacheIgnoreQueryString</a></li>
76<li><img alt="" src="/images/down.gif" /> <a href="#cacheignoreurlsessionidentifiers">CacheIgnoreURLSessionIdentifiers</a></li>
77<li><img alt="" src="/images/down.gif" /> <a href="#cachelastmodifiedfactor">CacheLastModifiedFactor</a></li>
78<li><img alt="" src="/images/down.gif" /> <a href="#cachelock">CacheLock</a></li>
79<li><img alt="" src="/images/down.gif" /> <a href="#cachelockmaxage">CacheLockMaxAge</a></li>
80<li><img alt="" src="/images/down.gif" /> <a href="#cachelockpath">CacheLockPath</a></li>
81<li><img alt="" src="/images/down.gif" /> <a href="#cachemaxexpire">CacheMaxExpire</a></li>
82<li><img alt="" src="/images/down.gif" /> <a href="#cachestorenostore">CacheStoreNoStore</a></li>
83<li><img alt="" src="/images/down.gif" /> <a href="#cachestoreprivate">CacheStorePrivate</a></li>
84</ul>
85<h3>Topics</h3>
86<ul id="topics">
87<li><img alt="" src="/images/down.gif" /> <a href="#related">Related Modules and Directives</a></li>
88<li><img alt="" src="/images/down.gif" /> <a href="#sampleconf">Sample Configuration</a></li>
89<li><img alt="" src="/images/down.gif" /> <a href="#thunderingherd">Avoiding the Thundering Herd</a></li>
90</ul><h3>See also</h3>
91<ul class="seealso">
92<li><a href="/caching.html">Caching Guide</a></li>
93</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
94<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
95<div class="section">
96<h2><a name="related" id="related">Related Modules and Directives</a></h2>
97    <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><li><code class="module"><a href="/mod/mod_mem_cache.html">mod_mem_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><li><code class="directive"><a href="/mod/mod_mem_cache.html#mcachesize">MCacheSize</a></code></li><li><code class="directive"><a href="/mod/mod_mem_cache.html#mcachemaxobjectcount">MCacheMaxObjectCount</a></code></li><li><code class="directive"><a href="/mod/mod_mem_cache.html#mcacheminobjectsize">MCacheMinObjectSize</a></code></li><li><code class="directive"><a href="/mod/mod_mem_cache.html#mcachemaxobjectsize">MCacheMaxObjectSize</a></code></li><li><code class="directive"><a href="/mod/mod_mem_cache.html#mcacheremovalalgorithm">MCacheRemovalAlgorithm</a></code></li><li><code class="directive"><a href="/mod/mod_mem_cache.html#mcachemaxstreamingbuffer">MCacheMaxStreamingBuffer</a></code></li></ul></td></tr></table>
98</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
99<div class="section">
100<h2><a name="sampleconf" id="sampleconf">Sample Configuration</a></h2>
101    <div class="example"><h3>Sample httpd.conf</h3><p><code>
102      #<br />
103      # Sample Cache Configuration<br />
104      #<br />
105      LoadModule cache_module modules/mod_cache.so<br />
106      <br />
107      &lt;IfModule mod_cache.c&gt;<br />
108      <span class="indent">
109        #LoadModule disk_cache_module modules/mod_disk_cache.so<br />
110        # If you want to use mod_disk_cache instead of mod_mem_cache,<br />
111        # uncomment the line above and comment out the LoadModule line below.<br />
112        &lt;IfModule mod_disk_cache.c&gt;<br />
113        <span class="indent">
114          CacheRoot c:/cacheroot<br />
115          CacheEnable disk  /<br />
116          CacheDirLevels 5<br />
117          CacheDirLength 3<br />
118        </span>
119        &lt;/IfModule&gt; <br />
120        <br />
121        LoadModule mem_cache_module modules/mod_mem_cache.so<br />
122        &lt;IfModule mod_mem_cache.c&gt;<br />
123        <span class="indent">
124          CacheEnable mem  /<br />
125          MCacheSize 4096<br />
126          MCacheMaxObjectCount 100<br />
127          MCacheMinObjectSize 1<br />
128          MCacheMaxObjectSize 2048<br />
129        </span>
130        &lt;/IfModule&gt;<br />
131        <br />
132        # When acting as a proxy, don't cache the list of security updates<br />
133        CacheDisable http://security.update.server/update-list/<br />
134      </span>
135      &lt;/IfModule&gt;
136    </code></p></div>
137</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
138<div class="section">
139<h2><a name="thunderingherd" id="thunderingherd">Avoiding the Thundering Herd</a></h2>
140  <p>When a cached entry becomes stale, <code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> will submit
141  a conditional request to the backend, which is expected to confirm whether the
142  cached entry is still fresh, and send an updated entity if not.</p>
143  <p>A small but finite amount of time exists between the time the cached entity
144  becomes stale, and the time the stale entity is fully refreshed. On a busy
145  server, a significant number of requests might arrive during this time, and
146  cause a <strong>thundering herd</strong> of requests to strike the backend
147  suddenly and unpredictably.</p>
148  <p>To keep the thundering herd at bay, the <code class="directive">CacheLock</code>
149  directive can be used to define a directory in which locks are created for
150  URLs <strong>in flight</strong>. The lock is used as a <strong>hint</strong>
151  by other requests to either suppress an attempt to cache (someone else has
152  gone to fetch the entity), or to indicate that a stale entry is being refreshed
153  (stale content will be returned in the mean time).
154  </p>
155  <h3>Initial caching of an entry</h3>
156    
157    <p>When an entity is cached for the first time, a lock will be created for the
158    entity until the response has been fully cached. During the lifetime of the
159    lock, the cache will suppress the second and subsequent attempt to cache the
160    same entity. While this doesn't hold back the thundering herd, it does stop
161    the cache attempting to cache the same entity multiple times simultaneously.
162    </p>
163  
164  <h3>Refreshment of a stale entry</h3>
165    
166    <p>When an entity reaches its freshness lifetime and becomes stale, a lock
167    will be created for the entity until the response has either been confirmed as
168    still fresh, or replaced by the backend. During the lifetime of the lock, the
169    second and subsequent incoming request will cause stale data to be returned,
170    and the thundering herd is kept at bay.</p>
171  
172  <h3>Locks and Cache-Control: no-cache</h3>
173    
174    <p>Locks are used as a <strong>hint only</strong> to enable the cache to be
175    more gentle on backend servers, however the lock can be overridden if necessary.
176    If the client sends a request with a Cache-Control header forcing a reload, any
177    lock that may be present will be ignored, and the client's request will be
178    honoured immediately and the cached entry refreshed.</p>
179    <p>As a further safety mechanism, locks have a configurable maximum age.
180    Once this age has been reached, the lock is removed, and a new request is
181    given the opportunity to create a new lock. This maximum age can be set using
182    the <code class="directive">CacheLockMaxAge</code> directive, and defaults to 5
183    seconds.
184    </p>
185  
186  <h3>Example configuration</h3>
187    
188    <div class="example"><h3>Enabling the cache lock</h3><p><code>
189      #<br />
190      # Enable the cache lock<br />
191      #<br />
192      &lt;IfModule mod_cache.c&gt;<br />
193      <span class="indent">
194        CacheLock on<br />
195        CacheLockPath /tmp/mod_cache-lock<br />
196        CacheLockMaxAge 5<br />
197      </span>
198      &lt;/IfModule&gt;
199    </code></p></div>
200  
201</div>
202<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
203<div class="directive-section"><h2><a name="CacheDefaultExpire" id="CacheDefaultExpire">CacheDefaultExpire</a> <a name="cachedefaultexpire" id="cachedefaultexpire">Directive</a></h2>
204<table class="directive">
205<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>
206<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDefaultExpire <var>seconds</var></code></td></tr>
207<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheDefaultExpire 3600 (one hour)</code></td></tr>
208<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
209<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
210<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
211</table>
212    <p>The <code class="directive">CacheDefaultExpire</code> directive specifies a default time,
213    in seconds, to cache a document if neither an expiry date nor last-modified date are provided
214    with the document. The value specified with the <code class="directive">CacheMaxExpire</code>
215    directive does <em>not</em> override this setting.</p>
216
217    <div class="example"><p><code>
218      CacheDefaultExpire 86400
219    </code></p></div>
220
221</div>
222<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
223<div class="directive-section"><h2><a name="CacheDisable" id="CacheDisable">CacheDisable</a> <a name="cachedisable" id="cachedisable">Directive</a></h2>
224<table class="directive">
225<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Disable caching of specified URLs</td></tr>
226<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDisable <var> url-string</var></code></td></tr>
227<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
228<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
229<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
230</table>
231    <p>The <code class="directive">CacheDisable</code> directive instructs
232    <code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> to <em>not</em> cache urls at or below
233    <var>url-string</var>.</p>
234
235    <div class="example"><h3>Example</h3><p><code>
236      CacheDisable /local_files
237    </code></p></div>
238
239    <p> The <code>no-cache</code> environment variable can be set to 
240    disable caching on a finer grained set of resources in versions
241    2.2.12 and later.</p>
242
243
244<h3>See also</h3>
245<ul>
246<li><a href="/env.html">Environment Variables in Apache</a></li>
247</ul>
248</div>
249<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
250<div class="directive-section"><h2><a name="CacheEnable" id="CacheEnable">CacheEnable</a> <a name="cacheenable" id="cacheenable">Directive</a></h2>
251<table class="directive">
252<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable caching of specified URLs using a specified storage
253manager</td></tr>
254<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>
255<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
256<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
257<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
258</table>
259    <p>The <code class="directive">CacheEnable</code> directive instructs
260    <code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> to cache urls at or below
261    <var>url-string</var>. The cache storage manager is specified with the
262    <var>cache_type</var> argument. <var>cache_type</var> <code> mem</code>
263    instructs <code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> to use the memory based storage
264    manager implemented by <code class="module"><a href="/mod/mod_mem_cache.html">mod_mem_cache</a></code>. 
265    <var>cache_type</var> <code>disk</code> instructs
266    <code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> to use the disk based storage manager
267    implemented by <code class="module"><a href="/mod/mod_disk_cache.html">mod_disk_cache</a></code>.
268    <var>cache_type</var> <code>fd</code> instructs
269    <code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code> to use the file descriptor cache implemented
270    by <code class="module"><a href="/mod/mod_mem_cache.html">mod_mem_cache</a></code>.</p>
271    <p>In the event that the URL space overlaps between different
272    <code class="directive">CacheEnable</code> directives (as in the example below),
273    each possible storage manager will be run until the first one that
274    actually processes the request. The order in which the storage managers are
275    run is determined by the order of the <code class="directive">CacheEnable</code>
276    directives in the configuration file.</p>
277
278    <div class="example"><p><code>
279      CacheEnable  mem   /manual<br />
280      CacheEnable  fd    /images<br />
281      CacheEnable  disk  /<br />
282    </code></p></div>
283
284    <p>When acting as a forward proxy server, <var>url-string</var> can
285    also be used to specify remote sites and proxy protocols which 
286    caching should be enabled for.</p>
287 
288    <div class="example"><p><code>
289      # Cache proxied url's<br />
290      CacheEnable  disk  /<br /><br />
291      # Cache FTP-proxied url's<br />
292      CacheEnable  disk  ftp://<br /><br />
293      # Cache content from www.apache.org<br />
294      CacheEnable  disk  http://www.apache.org/<br />
295    </code></p></div>
296
297    <p> The <code>no-cache</code> environment variable can be set to 
298    disable caching on a finer grained set of resources in versions
299    2.2.12 and later.</p>
300
301
302<h3>See also</h3>
303<ul>
304<li><a href="/env.html">Environment Variables in Apache</a></li>
305</ul>
306</div>
307<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
308<div class="directive-section"><h2><a name="CacheIgnoreCacheControl" id="CacheIgnoreCacheControl">CacheIgnoreCacheControl</a> <a name="cacheignorecachecontrol" id="cacheignorecachecontrol">Directive</a></h2>
309<table class="directive">
310<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore request to not serve cached content to client</td></tr>
311<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreCacheControl On|Off</code></td></tr>
312<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreCacheControl Off</code></td></tr>
313<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
314<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
315<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
316</table>
317    <p>Ordinarily, requests containing a Cache-Control: no-cache or
318    Pragma: no-cache header value will not be served from the cache.  The
319    <code class="directive">CacheIgnoreCacheControl</code> directive allows this
320    behavior to be overridden.  <code class="directive">CacheIgnoreCacheControl</code>
321    On tells the server to attempt to serve the resource from the cache even
322    if the request contains no-cache header values.  Resources requiring
323    authorization will <em>never</em> be cached.</p>
324
325    <div class="example"><p><code>
326      CacheIgnoreCacheControl On
327    </code></p></div>
328
329    <div class="warning"><h3>Warning:</h3>
330       This directive will allow serving from the cache even if the client has
331       requested that the document not be served from the cache.  This might
332       result in stale content being served.
333    </div>
334
335<h3>See also</h3>
336<ul>
337<li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li>
338<li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li>
339</ul>
340</div>
341<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
342<div class="directive-section"><h2><a name="CacheIgnoreHeaders" id="CacheIgnoreHeaders">CacheIgnoreHeaders</a> <a name="cacheignoreheaders" id="cacheignoreheaders">Directive</a></h2>
343<table class="directive">
344<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Do not store the given HTTP header(s) in the cache.
345</td></tr>
346<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>
347<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreHeaders None</code></td></tr>
348<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
349<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
350<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
351</table>
352    <p>According to RFC 2616, hop-by-hop HTTP headers are not stored in
353    the cache.  The following HTTP headers are hop-by-hop headers and thus
354    do not get stored in the cache in <em>any</em> case regardless of the
355    setting of <code class="directive">CacheIgnoreHeaders</code>:</p>
356
357    <ul>
358      <li><code>Connection</code></li>
359      <li><code>Keep-Alive</code></li>
360      <li><code>Proxy-Authenticate</code></li>
361      <li><code>Proxy-Authorization</code></li>
362      <li><code>TE</code></li>
363      <li><code>Trailers</code></li>
364      <li><code>Transfer-Encoding</code></li>
365      <li><code>Upgrade</code></li>
366    </ul>
367
368    <p><code class="directive">CacheIgnoreHeaders</code> specifies additional HTTP
369    headers that should not to be stored in the cache.  For example, it makes
370    sense in some cases to prevent cookies from being stored in the cache.</p>
371
372    <p><code class="directive">CacheIgnoreHeaders</code> takes a space separated list
373    of HTTP headers that should not be stored in the cache. If only hop-by-hop
374    headers not should be stored in the cache (the RFC 2616 compliant
375    behaviour), <code class="directive">CacheIgnoreHeaders</code> can be set to
376    <code>None</code>.</p>
377
378    <div class="example"><h3>Example 1</h3><p><code>
379      CacheIgnoreHeaders Set-Cookie
380    </code></p></div>
381
382    <div class="example"><h3>Example 2</h3><p><code>
383      CacheIgnoreHeaders None
384    </code></p></div>
385
386    <div class="warning"><h3>Warning:</h3>
387      If headers like <code>Expires</code> which are needed for proper cache
388      management are not stored due to a
389      <code class="directive">CacheIgnoreHeaders</code> setting, the behaviour of
390      mod_cache is undefined.
391    </div>
392
393</div>
394<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
395<div class="directive-section"><h2><a name="CacheIgnoreNoLastMod" id="CacheIgnoreNoLastMod">CacheIgnoreNoLastMod</a> <a name="cacheignorenolastmod" id="cacheignorenolastmod">Directive</a></h2>
396<table class="directive">
397<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore the fact that a response has no Last Modified
398header.</td></tr>
399<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreNoLastMod On|Off</code></td></tr>
400<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreNoLastMod Off</code></td></tr>
401<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
402<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
403<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
404</table>
405    <p>Ordinarily, documents without a last-modified date are not cached.
406    Under some circumstances the last-modified date is removed (during
407    <code class="module"><a href="/mod/mod_include.html">mod_include</a></code> processing for example) or not provided
408    at all. The <code class="directive">CacheIgnoreNoLastMod</code> directive
409    provides a way to specify that documents without last-modified dates
410    should be considered for caching, even without a last-modified date.
411    If neither a last-modified date nor an expiry date are provided with
412    the document then the value specified by the
413    <code class="directive">CacheDefaultExpire</code> directive will be used to
414    generate an expiration date.</p>
415
416    <div class="example"><p><code>
417      CacheIgnoreNoLastMod On
418    </code></p></div>
419
420</div>
421<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
422<div class="directive-section"><h2><a name="CacheIgnoreQueryString" id="CacheIgnoreQueryString">CacheIgnoreQueryString</a> <a name="cacheignorequerystring" id="cacheignorequerystring">Directive</a></h2>
423<table class="directive">
424<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore query string when caching</td></tr>
425<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreQueryString On|Off</code></td></tr>
426<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreQueryString Off</code></td></tr>
427<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
428<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
429<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
430<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.2.6 and later</td></tr>
431</table>
432    <p>Ordinarily, requests with query string parameters are cached separately
433    for each unique query string. This is according to RFC 2616/13.9 done only
434    if an expiration time is specified. The 
435    <code class="directive">CacheIgnoreQueryString</code> directive tells the cache to
436    cache requests even if no expiration time is specified, and to reply with 
437    a cached reply even if the query string differs. From a caching point of
438    view the request is treated as if having no query string when this 
439    directive is enabled.</p>
440
441    <div class="example"><p><code>
442      CacheIgnoreQueryString On
443    </code></p></div>
444
445
446</div>
447<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
448<div class="directive-section"><h2><a name="CacheIgnoreURLSessionIdentifiers" id="CacheIgnoreURLSessionIdentifiers">CacheIgnoreURLSessionIdentifiers</a> <a name="cacheignoreurlsessionidentifiers" id="cacheignoreurlsessionidentifiers">Directive</a></h2>
449<table class="directive">
450<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore defined session identifiers encoded in the URL when caching
451</td></tr>
452<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreURLSessionIdentifiers <var>identifier</var> [<var>identifier</var>] ...</code></td></tr>
453<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreURLSessionIdentifiers None</code></td></tr>
454<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
455<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
456<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
457</table>
458    <p>Sometimes applications encode the session identifier into the URL like in the following
459    Examples:
460    </p>
461    <ul>
462      <li><code>/someapplication/image.gif;jsessionid=123456789</code></li>
463      <li><code>/someapplication/image.gif?PHPSESSIONID=12345678</code></li>
464    </ul>
465    <p>This causes cachable resources to be stored separately for each session, which
466    is often not desired. <code class="directive">CacheIgnoreURLSessionIdentifiers</code> lets
467    define a list of identifiers that are removed from the key that is used to identify
468    an entity in the cache, such that cachable resources are not stored separately for
469    each session.
470    </p>
471    <p><code>CacheIgnoreURLSessionIdentifiers None</code> clears the list of ignored
472    identifiers. Otherwise, each identifier is added to the list.</p>
473
474    <div class="example"><h3>Example 1</h3><p><code>
475      CacheIgnoreURLSessionIdentifiers jsessionid
476    </code></p></div>
477
478    <div class="example"><h3>Example 2</h3><p><code>
479      CacheIgnoreURLSessionIdentifiers None
480    </code></p></div>
481
482
483</div>
484<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
485<div class="directive-section"><h2><a name="CacheLastModifiedFactor" id="CacheLastModifiedFactor">CacheLastModifiedFactor</a> <a name="cachelastmodifiedfactor" id="cachelastmodifiedfactor">Directive</a></h2>
486<table class="directive">
487<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The factor used to compute an expiry date based on the
488LastModified date.</td></tr>
489<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLastModifiedFactor <var>float</var></code></td></tr>
490<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLastModifiedFactor 0.1</code></td></tr>
491<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
492<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
493<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
494</table>
495    <p>In the event that a document does not provide an expiry date but does
496    provide a last-modified date, an expiry date can be calculated based on
497    the time since the document was last modified. The
498    <code class="directive">CacheLastModifiedFactor</code> directive specifies a
499    <var>factor</var> to be used in the generation of this expiry date
500    according to the following formula:
501
502    <code>expiry-period = time-since-last-modified-date * <var>factor</var>
503    expiry-date = current-date + expiry-period</code>
504
505    For example, if the document was last modified 10 hours ago, and
506    <var>factor</var> is 0.1 then the expiry-period will be set to
507    10*0.1 = 1 hour. If the current time was 3:00pm then the computed
508    expiry-date would be 3:00pm + 1hour = 4:00pm.
509
510    If the expiry-period would be longer than that set by
511    <code class="directive">CacheMaxExpire</code>, then the latter takes
512    precedence.</p>
513
514    <div class="example"><p><code>
515      CacheLastModifiedFactor 0.5
516    </code></p></div>
517
518</div>
519<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
520<div class="directive-section"><h2><a name="CacheLock" id="CacheLock">CacheLock</a> <a name="cachelock" id="cachelock">Directive</a></h2>
521<table class="directive">
522<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable the thundering herd lock.</td></tr>
523<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLock <var>on|off</var></code></td></tr>
524<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLock off</code></td></tr>
525<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
526<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
527<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
528<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.2.15 and later</td></tr>
529</table>
530  <p>The <code class="directive">CacheLock</code> directive enables the thundering herd lock
531  for the given URL space.</p>
532  
533  <p>In a minimal configuration the following directive is all that is needed to
534  enable the thundering herd lock in the default system temp directory.</p>
535
536  <div class="example"><p><code>
537    # Enable chache lock<br />
538    CacheLock on<br /><br />
539  </code></p></div>
540
541
542</div>
543<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
544<div class="directive-section"><h2><a name="CacheLockMaxAge" id="CacheLockMaxAge">CacheLockMaxAge</a> <a name="cachelockmaxage" id="cachelockmaxage">Directive</a></h2>
545<table class="directive">
546<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the maximum possible age of a cache lock.</td></tr>
547<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockMaxAge <var>integer</var></code></td></tr>
548<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockMaxAge 5</code></td></tr>
549<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
550<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
551<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
552</table>
553  <p>The <code class="directive">CacheLockMaxAge</code> directive specifies the maximum
554  age of any cache lock.</p>
555  
556  <p>A lock older than this value in seconds will be ignored, and the next
557  incoming request will be given the opportunity to re-establish the lock.
558  This mechanism prevents a slow client taking an excessively long time to refresh
559  an entity.</p>
560  
561
562</div>
563<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
564<div class="directive-section"><h2><a name="CacheLockPath" id="CacheLockPath">CacheLockPath</a> <a name="cachelockpath" id="cachelockpath">Directive</a></h2>
565<table class="directive">
566<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the lock path directory.</td></tr>
567<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockPath <var>directory</var></code></td></tr>
568<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockPath /tmp/mod_cache-lock</code></td></tr>
569<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
570<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
571<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
572</table>
573  <p>The <code class="directive">CacheLockPath</code> directive allows you to specify the
574  directory in which the locks are created. By default, the system's temporary
575  folder is used. Locks consist of empty files that only exist for stale URLs
576  in flight, so is significantly less resource intensive than the traditional
577  disk cache.</p>
578
579
580</div>
581<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
582<div class="directive-section"><h2><a name="CacheMaxExpire" id="CacheMaxExpire">CacheMaxExpire</a> <a name="cachemaxexpire" id="cachemaxexpire">Directive</a></h2>
583<table class="directive">
584<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum time in seconds to cache a document</td></tr>
585<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMaxExpire <var>seconds</var></code></td></tr>
586<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMaxExpire 86400 (one day)</code></td></tr>
587<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
588<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
589<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
590</table>
591    <p>The <code class="directive">CacheMaxExpire</code> directive specifies the maximum number of
592    seconds for which cachable HTTP documents will be retained without checking the origin
593    server. Thus, documents will be out of date at most this number of seconds. This maximum
594    value is enforced even if an expiry date was supplied with the document.</p>
595
596    <div class="example"><p><code>
597      CacheMaxExpire 604800
598    </code></p></div>
599
600</div>
601<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
602<div class="directive-section"><h2><a name="CacheStoreNoStore" id="CacheStoreNoStore">CacheStoreNoStore</a> <a name="cachestorenostore" id="cachestorenostore">Directive</a></h2>
603<table class="directive">
604<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>
605<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStoreNoStore On|Off</code></td></tr>
606<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStoreNoStore Off</code></td></tr>
607<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
608<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
609<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
610</table>
611    <p>Ordinarily, requests or responses with Cache-Control: no-store header
612       values will not be stored in the cache.  The
613       <code class="directive">CacheStoreNoStore</code> directive allows this
614       behavior to be overridden.  <code class="directive">CacheStoreNoStore</code> On
615       tells the server to attempt to cache the resource even if it contains
616       no-store header values.  Resources requiring authorization will
617       <em>never</em> be cached.</p>
618
619    <div class="example"><p><code>
620      CacheStoreNoStore On
621    </code></p></div>
622
623    <div class="warning"><h3>Warning:</h3>
624       As described in RFC 2616, the no-store directive is intended to
625       "prevent the inadvertent release or retention of sensitive information
626       (for example, on backup tapes)."  Enabling this option could store
627       sensitive information in the cache.  You are hereby warned.
628    </div>
629
630<h3>See also</h3>
631<ul>
632<li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li>
633<li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li>
634</ul>
635</div>
636<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
637<div class="directive-section"><h2><a name="CacheStorePrivate" id="CacheStorePrivate">CacheStorePrivate</a> <a name="cachestoreprivate" id="cachestoreprivate">Directive</a></h2>
638<table class="directive">
639<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>
640<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStorePrivate On|Off</code></td></tr>
641<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStorePrivate Off</code></td></tr>
642<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
643<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
644<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr>
645</table>
646    <p>Ordinarily, responses with Cache-Control: private header values will not
647       be stored in the cache.  The <code class="directive">CacheStorePrivate</code>
648       directive allows this behavior to be overridden.
649       <code class="directive">CacheStorePrivate</code> On
650       tells the server to attempt to cache the resource even if it contains
651       private header values.  Resources requiring authorization will
652       <em>never</em> be cached.</p>
653
654    <div class="example"><p><code>
655      CacheStorePrivate On
656    </code></p></div>
657
658    <div class="warning"><h3>Warning:</h3>
659       This directive will allow caching even if the upstream server has
660       requested that the resource not be cached.  This directive is only
661       ideal for a 'private' cache.
662    </div>
663
664<h3>See also</h3>
665<ul>
666<li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li>
667<li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li>
668</ul>
669</div>
670</div>
671<div class="bottomlang">
672<p><span>Available Languages: </span><a href="/en/mod/mod_cache.html" title="English">&nbsp;en&nbsp;</a> |
673<a href="/ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
674<a href="/ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a></p>
675</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&amp;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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