github.com/krum110487/go-htaccess@v0.0.0-20240316004156-60641c8e7598/tests/data/apache_2_2_34/manual/mod/mod_cache.html.en (about) 1 <?xml version="1.0" encoding="ISO-8859-1"?> 2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> 3 <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head> 4 <meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type" /> 5 <!-- 6 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 7 This file is generated from xml source: DO NOT EDIT 8 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX 9 --> 10 <title>mod_cache - Apache HTTP Server Version 2.2</title> 11 <link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> 12 <link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> 13 <link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="../style/css/prettify.css" /> 14 <script src="../style/scripts/prettify.min.js" type="text/javascript"> 15 </script> 16 17 <link href="../images/favicon.ico" rel="shortcut icon" /><link href="http://httpd.apache.org/docs/current/mod/mod_cache.html" rel="canonical" /></head> 18 <body> 19 <div id="page-header"> 20 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p> 21 <p class="apache">Apache HTTP Server Version 2.2</p> 22 <img alt="" src="../images/feather.gif" /></div> 23 <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div> 24 <div id="path"> 25 <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.2</a> > <a href="./">Modules</a></div> 26 <div id="page-content"> 27 <div class="retired"><h4>Please note</h4> 28 <p> This document refers to a legacy release (<strong>2.2</strong>) of Apache httpd. The active release (<strong>2.4</strong>) is documented <a href="http://httpd.apache.org/docs/current">here</a>. If you have not already upgraded, please follow <a href="http://httpd.apache.org/docs/current/upgrading.html">this link</a> for more information.</p> 29 <p>You may follow <a href="http://httpd.apache.org/docs/current/mod/mod_cache.html">this link</a> to go to the current version of this document.</p></div><div id="preamble"><h1>Apache Module mod_cache</h1> 30 <div class="toplang"> 31 <p><span>Available Languages: </span><a href="../en/mod/mod_cache.html" title="English"> en </a> | 32 <a href="../ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | 33 <a href="../ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p> 34 </div> 35 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Content cache keyed to URIs.</td></tr> 36 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr> 37 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>cache_module</td></tr> 38 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_cache.c</td></tr></table> 39 <h3>Summary</h3> 40 41 <div class="warning">This module should be used with care and 42 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 43 should not enable caching for any content to which you wish 44 to limit access by client host name, address or environment 45 variable.</div> 46 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 HTTP 48 content cache that can be used to cache either local or proxied content. 49 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> requires the services of one or more storage 50 management modules. Two storage management modules are included in 51 the base Apache distribution:</p> 52 <dl> 53 <dt><code class="module"><a href="../mod/mod_disk_cache.html">mod_disk_cache</a></code></dt> 54 <dd>implements a disk based storage manager.</dd> 55 56 <dt><code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code></dt> 57 <dd>implements a memory based storage manager. 58 <code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code> can be configured to operate in two 59 modes: caching open file descriptors or caching objects in heap storage. 60 <code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code> can be used to cache locally generated content 61 or to cache backend server content for <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> when 62 configured using <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code> 63 (aka <dfn>reverse proxy</dfn>)</dd> 64 </dl> 65 66 <p>Content is stored in and retrieved from the cache using URI based keys. Content with 67 access protection is not cached.</p> 68 <p>Further details, discussion, and examples, are provided in the 69 <a href="../caching.html">Caching Guide</a>.</p> 70 </div> 71 <div id="quickview"><h3>Topics</h3> 72 <ul id="topics"> 73 <li><img alt="" src="../images/down.gif" /> <a href="#related">Related Modules and Directives</a></li> 74 <li><img alt="" src="../images/down.gif" /> <a href="#sampleconf">Sample Configuration</a></li> 75 <li><img alt="" src="../images/down.gif" /> <a href="#thunderingherd">Avoiding the Thundering Herd</a></li> 76 </ul><h3 class="directives">Directives</h3> 77 <ul id="toc"> 78 <li><img alt="" src="../images/down.gif" /> <a href="#cachedefaultexpire">CacheDefaultExpire</a></li> 79 <li><img alt="" src="../images/down.gif" /> <a href="#cachedisable">CacheDisable</a></li> 80 <li><img alt="" src="../images/down.gif" /> <a href="#cacheenable">CacheEnable</a></li> 81 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></li> 82 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignoreheaders">CacheIgnoreHeaders</a></li> 83 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignorenolastmod">CacheIgnoreNoLastMod</a></li> 84 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignorequerystring">CacheIgnoreQueryString</a></li> 85 <li><img alt="" src="../images/down.gif" /> <a href="#cacheignoreurlsessionidentifiers">CacheIgnoreURLSessionIdentifiers</a></li> 86 <li><img alt="" src="../images/down.gif" /> <a href="#cachelastmodifiedfactor">CacheLastModifiedFactor</a></li> 87 <li><img alt="" src="../images/down.gif" /> <a href="#cachelock">CacheLock</a></li> 88 <li><img alt="" src="../images/down.gif" /> <a href="#cachelockmaxage">CacheLockMaxAge</a></li> 89 <li><img alt="" src="../images/down.gif" /> <a href="#cachelockpath">CacheLockPath</a></li> 90 <li><img alt="" src="../images/down.gif" /> <a href="#cachemaxexpire">CacheMaxExpire</a></li> 91 <li><img alt="" src="../images/down.gif" /> <a href="#cachestorenostore">CacheStoreNoStore</a></li> 92 <li><img alt="" src="../images/down.gif" /> <a href="#cachestoreprivate">CacheStorePrivate</a></li> 93 </ul> 94 <h3>See also</h3> 95 <ul class="seealso"> 96 <li><a href="../caching.html">Caching Guide</a></li> 97 </ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div> 98 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 99 <div class="section"> 100 <h2><a name="related" id="related">Related Modules and Directives</a></h2> 101 <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> 102 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 103 <div class="section"> 104 <h2><a name="sampleconf" id="sampleconf">Sample Configuration</a></h2> 105 <div class="example"><h3>Sample httpd.conf</h3><p><code> 106 #<br /> 107 # Sample Cache Configuration<br /> 108 #<br /> 109 LoadModule cache_module modules/mod_cache.so<br /> 110 <br /> 111 <IfModule mod_cache.c><br /> 112 <span class="indent"> 113 #LoadModule disk_cache_module modules/mod_disk_cache.so<br /> 114 # If you want to use mod_disk_cache instead of mod_mem_cache,<br /> 115 # uncomment the line above and comment out the LoadModule line below.<br /> 116 <IfModule mod_disk_cache.c><br /> 117 <span class="indent"> 118 CacheRoot c:/cacheroot<br /> 119 CacheEnable disk /<br /> 120 CacheDirLevels 5<br /> 121 CacheDirLength 3<br /> 122 </span> 123 </IfModule> <br /> 124 <br /> 125 LoadModule mem_cache_module modules/mod_mem_cache.so<br /> 126 <IfModule mod_mem_cache.c><br /> 127 <span class="indent"> 128 CacheEnable mem /<br /> 129 MCacheSize 4096<br /> 130 MCacheMaxObjectCount 100<br /> 131 MCacheMinObjectSize 1<br /> 132 MCacheMaxObjectSize 2048<br /> 133 </span> 134 </IfModule><br /> 135 <br /> 136 # When acting as a proxy, don't cache the list of security updates<br /> 137 CacheDisable http://security.update.server/update-list/<br /> 138 </span> 139 </IfModule> 140 </code></p></div> 141 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 142 <div class="section"> 143 <h2><a name="thunderingherd" id="thunderingherd">Avoiding the Thundering Herd</a></h2> 144 <p>When a cached entry becomes stale, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> will submit 145 a conditional request to the backend, which is expected to confirm whether the 146 cached entry is still fresh, and send an updated entity if not.</p> 147 <p>A small but finite amount of time exists between the time the cached entity 148 becomes stale, and the time the stale entity is fully refreshed. On a busy 149 server, a significant number of requests might arrive during this time, and 150 cause a <strong>thundering herd</strong> of requests to strike the backend 151 suddenly and unpredictably.</p> 152 <p>To keep the thundering herd at bay, the <code class="directive">CacheLock</code> 153 directive can be used to define a directory in which locks are created for 154 URLs <strong>in flight</strong>. The lock is used as a <strong>hint</strong> 155 by other requests to either suppress an attempt to cache (someone else has 156 gone to fetch the entity), or to indicate that a stale entry is being refreshed 157 (stale content will be returned in the mean time). 158 </p> 159 <h3>Initial caching of an entry</h3> 160 161 <p>When an entity is cached for the first time, a lock will be created for the 162 entity until the response has been fully cached. During the lifetime of the 163 lock, the cache will suppress the second and subsequent attempt to cache the 164 same entity. While this doesn't hold back the thundering herd, it does stop 165 the cache attempting to cache the same entity multiple times simultaneously. 166 </p> 167 168 <h3>Refreshment of a stale entry</h3> 169 170 <p>When an entity reaches its freshness lifetime and becomes stale, a lock 171 will be created for the entity until the response has either been confirmed as 172 still fresh, or replaced by the backend. During the lifetime of the lock, the 173 second and subsequent incoming request will cause stale data to be returned, 174 and the thundering herd is kept at bay.</p> 175 176 <h3>Locks and Cache-Control: no-cache</h3> 177 178 <p>Locks are used as a <strong>hint only</strong> to enable the cache to be 179 more gentle on backend servers, however the lock can be overridden if necessary. 180 If the client sends a request with a Cache-Control header forcing a reload, any 181 lock that may be present will be ignored, and the client's request will be 182 honoured immediately and the cached entry refreshed.</p> 183 <p>As a further safety mechanism, locks have a configurable maximum age. 184 Once this age has been reached, the lock is removed, and a new request is 185 given the opportunity to create a new lock. This maximum age can be set using 186 the <code class="directive">CacheLockMaxAge</code> directive, and defaults to 5 187 seconds. 188 </p> 189 190 <h3>Example configuration</h3> 191 192 <div class="example"><h3>Enabling the cache lock</h3><p><code> 193 #<br /> 194 # Enable the cache lock<br /> 195 #<br /> 196 <IfModule mod_cache.c><br /> 197 <span class="indent"> 198 CacheLock on<br /> 199 CacheLockPath /tmp/mod_cache-lock<br /> 200 CacheLockMaxAge 5<br /> 201 </span> 202 </IfModule> 203 </code></p></div> 204 205 </div> 206 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 207 <div class="directive-section"><h2><a name="CacheDefaultExpire" id="CacheDefaultExpire">CacheDefaultExpire</a> <a name="cachedefaultexpire" id="cachedefaultexpire">Directive</a></h2> 208 <table class="directive"> 209 <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> 210 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDefaultExpire <var>seconds</var></code></td></tr> 211 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheDefaultExpire 3600 (one hour)</code></td></tr> 212 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 213 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 214 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 215 </table> 216 <p>The <code class="directive">CacheDefaultExpire</code> directive specifies a default time, 217 in seconds, to cache a document if neither an expiry date nor last-modified date are provided 218 with the document. The value specified with the <code class="directive">CacheMaxExpire</code> 219 directive does <em>not</em> override this setting.</p> 220 221 <div class="example"><p><code> 222 CacheDefaultExpire 86400 223 </code></p></div> 224 225 </div> 226 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 227 <div class="directive-section"><h2><a name="CacheDisable" id="CacheDisable">CacheDisable</a> <a name="cachedisable" id="cachedisable">Directive</a></h2> 228 <table class="directive"> 229 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Disable caching of specified URLs</td></tr> 230 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDisable <var> url-string</var></code></td></tr> 231 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 232 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 233 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 234 </table> 235 <p>The <code class="directive">CacheDisable</code> directive instructs 236 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to <em>not</em> cache urls at or below 237 <var>url-string</var>.</p> 238 239 <div class="example"><h3>Example</h3><p><code> 240 CacheDisable /local_files 241 </code></p></div> 242 243 <p> The <code>no-cache</code> environment variable can be set to 244 disable caching on a finer grained set of resources in versions 245 2.2.12 and later.</p> 246 247 248 <h3>See also</h3> 249 <ul> 250 <li><a href="../env.html">Environment Variables in Apache</a></li> 251 </ul> 252 </div> 253 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 254 <div class="directive-section"><h2><a name="CacheEnable" id="CacheEnable">CacheEnable</a> <a name="cacheenable" id="cacheenable">Directive</a></h2> 255 <table class="directive"> 256 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable caching of specified URLs using a specified storage 257 manager</td></tr> 258 <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> 259 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 260 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 261 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 262 </table> 263 <p>The <code class="directive">CacheEnable</code> directive instructs 264 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to cache urls at or below 265 <var>url-string</var>. The cache storage manager is specified with the 266 <var>cache_type</var> argument. <var>cache_type</var> <code> mem</code> 267 instructs <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the memory based storage 268 manager implemented by <code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code>. 269 <var>cache_type</var> <code>disk</code> instructs 270 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the disk based storage manager 271 implemented by <code class="module"><a href="../mod/mod_disk_cache.html">mod_disk_cache</a></code>. 272 <var>cache_type</var> <code>fd</code> instructs 273 <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the file descriptor cache implemented 274 by <code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code>.</p> 275 <p>In the event that the URL space overlaps between different 276 <code class="directive">CacheEnable</code> directives (as in the example below), 277 each possible storage manager will be run until the first one that 278 actually processes the request. The order in which the storage managers are 279 run is determined by the order of the <code class="directive">CacheEnable</code> 280 directives in the configuration file.</p> 281 282 <div class="example"><p><code> 283 CacheEnable mem /manual<br /> 284 CacheEnable fd /images<br /> 285 CacheEnable disk /<br /> 286 </code></p></div> 287 288 <p>When acting as a forward proxy server, <var>url-string</var> can 289 also be used to specify remote sites and proxy protocols which 290 caching should be enabled for.</p> 291 292 <div class="example"><p><code> 293 # Cache proxied url's<br /> 294 CacheEnable disk /<br /><br /> 295 # Cache FTP-proxied url's<br /> 296 CacheEnable disk ftp://<br /><br /> 297 # Cache content from www.apache.org<br /> 298 CacheEnable disk http://www.apache.org/<br /> 299 </code></p></div> 300 301 <p> The <code>no-cache</code> environment variable can be set to 302 disable caching on a finer grained set of resources in versions 303 2.2.12 and later.</p> 304 305 306 <h3>See also</h3> 307 <ul> 308 <li><a href="../env.html">Environment Variables in Apache</a></li> 309 </ul> 310 </div> 311 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 312 <div class="directive-section"><h2><a name="CacheIgnoreCacheControl" id="CacheIgnoreCacheControl">CacheIgnoreCacheControl</a> <a name="cacheignorecachecontrol" id="cacheignorecachecontrol">Directive</a></h2> 313 <table class="directive"> 314 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore request to not serve cached content to client</td></tr> 315 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreCacheControl On|Off</code></td></tr> 316 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreCacheControl Off</code></td></tr> 317 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 318 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 319 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 320 </table> 321 <p>Ordinarily, requests containing a Cache-Control: no-cache or 322 Pragma: no-cache header value will not be served from the cache. The 323 <code class="directive">CacheIgnoreCacheControl</code> directive allows this 324 behavior to be overridden. <code class="directive">CacheIgnoreCacheControl</code> 325 On tells the server to attempt to serve the resource from the cache even 326 if the request contains no-cache header values. Resources requiring 327 authorization will <em>never</em> be cached.</p> 328 329 <div class="example"><p><code> 330 CacheIgnoreCacheControl On 331 </code></p></div> 332 333 <div class="warning"><h3>Warning:</h3> 334 This directive will allow serving from the cache even if the client has 335 requested that the document not be served from the cache. This might 336 result in stale content being served. 337 </div> 338 339 <h3>See also</h3> 340 <ul> 341 <li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li> 342 <li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li> 343 </ul> 344 </div> 345 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 346 <div class="directive-section"><h2><a name="CacheIgnoreHeaders" id="CacheIgnoreHeaders">CacheIgnoreHeaders</a> <a name="cacheignoreheaders" id="cacheignoreheaders">Directive</a></h2> 347 <table class="directive"> 348 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Do not store the given HTTP header(s) in the cache. 349 </td></tr> 350 <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> 351 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreHeaders None</code></td></tr> 352 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 353 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 354 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 355 </table> 356 <p>According to RFC 2616, hop-by-hop HTTP headers are not stored in 357 the cache. The following HTTP headers are hop-by-hop headers and thus 358 do not get stored in the cache in <em>any</em> case regardless of the 359 setting of <code class="directive">CacheIgnoreHeaders</code>:</p> 360 361 <ul> 362 <li><code>Connection</code></li> 363 <li><code>Keep-Alive</code></li> 364 <li><code>Proxy-Authenticate</code></li> 365 <li><code>Proxy-Authorization</code></li> 366 <li><code>TE</code></li> 367 <li><code>Trailers</code></li> 368 <li><code>Transfer-Encoding</code></li> 369 <li><code>Upgrade</code></li> 370 </ul> 371 372 <p><code class="directive">CacheIgnoreHeaders</code> specifies additional HTTP 373 headers that should not to be stored in the cache. For example, it makes 374 sense in some cases to prevent cookies from being stored in the cache.</p> 375 376 <p><code class="directive">CacheIgnoreHeaders</code> takes a space separated list 377 of HTTP headers that should not be stored in the cache. If only hop-by-hop 378 headers not should be stored in the cache (the RFC 2616 compliant 379 behaviour), <code class="directive">CacheIgnoreHeaders</code> can be set to 380 <code>None</code>.</p> 381 382 <div class="example"><h3>Example 1</h3><p><code> 383 CacheIgnoreHeaders Set-Cookie 384 </code></p></div> 385 386 <div class="example"><h3>Example 2</h3><p><code> 387 CacheIgnoreHeaders None 388 </code></p></div> 389 390 <div class="warning"><h3>Warning:</h3> 391 If headers like <code>Expires</code> which are needed for proper cache 392 management are not stored due to a 393 <code class="directive">CacheIgnoreHeaders</code> setting, the behaviour of 394 mod_cache is undefined. 395 </div> 396 397 </div> 398 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 399 <div class="directive-section"><h2><a name="CacheIgnoreNoLastMod" id="CacheIgnoreNoLastMod">CacheIgnoreNoLastMod</a> <a name="cacheignorenolastmod" id="cacheignorenolastmod">Directive</a></h2> 400 <table class="directive"> 401 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore the fact that a response has no Last Modified 402 header.</td></tr> 403 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreNoLastMod On|Off</code></td></tr> 404 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreNoLastMod Off</code></td></tr> 405 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 406 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 407 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 408 </table> 409 <p>Ordinarily, documents without a last-modified date are not cached. 410 Under some circumstances the last-modified date is removed (during 411 <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> processing for example) or not provided 412 at all. The <code class="directive">CacheIgnoreNoLastMod</code> directive 413 provides a way to specify that documents without last-modified dates 414 should be considered for caching, even without a last-modified date. 415 If neither a last-modified date nor an expiry date are provided with 416 the document then the value specified by the 417 <code class="directive">CacheDefaultExpire</code> directive will be used to 418 generate an expiration date.</p> 419 420 <div class="example"><p><code> 421 CacheIgnoreNoLastMod On 422 </code></p></div> 423 424 </div> 425 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 426 <div class="directive-section"><h2><a name="CacheIgnoreQueryString" id="CacheIgnoreQueryString">CacheIgnoreQueryString</a> <a name="cacheignorequerystring" id="cacheignorequerystring">Directive</a></h2> 427 <table class="directive"> 428 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore query string when caching</td></tr> 429 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreQueryString On|Off</code></td></tr> 430 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreQueryString Off</code></td></tr> 431 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 432 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 433 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 434 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.2.6 and later</td></tr> 435 </table> 436 <p>Ordinarily, requests with query string parameters are cached separately 437 for each unique query string. This is according to RFC 2616/13.9 done only 438 if an expiration time is specified. The 439 <code class="directive">CacheIgnoreQueryString</code> directive tells the cache to 440 cache requests even if no expiration time is specified, and to reply with 441 a cached reply even if the query string differs. From a caching point of 442 view the request is treated as if having no query string when this 443 directive is enabled.</p> 444 445 <div class="example"><p><code> 446 CacheIgnoreQueryString On 447 </code></p></div> 448 449 450 </div> 451 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 452 <div class="directive-section"><h2><a name="CacheIgnoreURLSessionIdentifiers" id="CacheIgnoreURLSessionIdentifiers">CacheIgnoreURLSessionIdentifiers</a> <a name="cacheignoreurlsessionidentifiers" id="cacheignoreurlsessionidentifiers">Directive</a></h2> 453 <table class="directive"> 454 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore defined session identifiers encoded in the URL when caching 455 </td></tr> 456 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreURLSessionIdentifiers <var>identifier</var> [<var>identifier</var>] ...</code></td></tr> 457 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreURLSessionIdentifiers None</code></td></tr> 458 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 459 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 460 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 461 </table> 462 <p>Sometimes applications encode the session identifier into the URL like in the following 463 Examples: 464 </p> 465 <ul> 466 <li><code>/someapplication/image.gif;jsessionid=123456789</code></li> 467 <li><code>/someapplication/image.gif?PHPSESSIONID=12345678</code></li> 468 </ul> 469 <p>This causes cachable resources to be stored separately for each session, which 470 is often not desired. <code class="directive">CacheIgnoreURLSessionIdentifiers</code> lets 471 define a list of identifiers that are removed from the key that is used to identify 472 an entity in the cache, such that cachable resources are not stored separately for 473 each session. 474 </p> 475 <p><code>CacheIgnoreURLSessionIdentifiers None</code> clears the list of ignored 476 identifiers. Otherwise, each identifier is added to the list.</p> 477 478 <div class="example"><h3>Example 1</h3><p><code> 479 CacheIgnoreURLSessionIdentifiers jsessionid 480 </code></p></div> 481 482 <div class="example"><h3>Example 2</h3><p><code> 483 CacheIgnoreURLSessionIdentifiers None 484 </code></p></div> 485 486 487 </div> 488 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 489 <div class="directive-section"><h2><a name="CacheLastModifiedFactor" id="CacheLastModifiedFactor">CacheLastModifiedFactor</a> <a name="cachelastmodifiedfactor" id="cachelastmodifiedfactor">Directive</a></h2> 490 <table class="directive"> 491 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The factor used to compute an expiry date based on the 492 LastModified date.</td></tr> 493 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLastModifiedFactor <var>float</var></code></td></tr> 494 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLastModifiedFactor 0.1</code></td></tr> 495 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 496 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 497 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 498 </table> 499 <p>In the event that a document does not provide an expiry date but does 500 provide a last-modified date, an expiry date can be calculated based on 501 the time since the document was last modified. The 502 <code class="directive">CacheLastModifiedFactor</code> directive specifies a 503 <var>factor</var> to be used in the generation of this expiry date 504 according to the following formula: 505 506 <code>expiry-period = time-since-last-modified-date * <var>factor</var> 507 expiry-date = current-date + expiry-period</code> 508 509 For example, if the document was last modified 10 hours ago, and 510 <var>factor</var> is 0.1 then the expiry-period will be set to 511 10*0.1 = 1 hour. If the current time was 3:00pm then the computed 512 expiry-date would be 3:00pm + 1hour = 4:00pm. 513 514 If the expiry-period would be longer than that set by 515 <code class="directive">CacheMaxExpire</code>, then the latter takes 516 precedence.</p> 517 518 <div class="example"><p><code> 519 CacheLastModifiedFactor 0.5 520 </code></p></div> 521 522 </div> 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="CacheLock" id="CacheLock">CacheLock</a> <a name="cachelock" id="cachelock">Directive</a></h2> 525 <table class="directive"> 526 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable the thundering herd lock.</td></tr> 527 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLock <var>on|off</var></code></td></tr> 528 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLock off</code></td></tr> 529 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</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 2.2.15 and later</td></tr> 533 </table> 534 <p>The <code class="directive">CacheLock</code> directive enables the thundering herd lock 535 for the given URL space.</p> 536 537 <p>In a minimal configuration the following directive is all that is needed to 538 enable the thundering herd lock in the default system temp directory.</p> 539 540 <div class="example"><p><code> 541 # Enable chache lock<br /> 542 CacheLock on<br /><br /> 543 </code></p></div> 544 545 546 </div> 547 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 548 <div class="directive-section"><h2><a name="CacheLockMaxAge" id="CacheLockMaxAge">CacheLockMaxAge</a> <a name="cachelockmaxage" id="cachelockmaxage">Directive</a></h2> 549 <table class="directive"> 550 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the maximum possible age of a cache lock.</td></tr> 551 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockMaxAge <var>integer</var></code></td></tr> 552 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockMaxAge 5</code></td></tr> 553 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 554 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 555 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 556 </table> 557 <p>The <code class="directive">CacheLockMaxAge</code> directive specifies the maximum 558 age of any cache lock.</p> 559 560 <p>A lock older than this value in seconds will be ignored, and the next 561 incoming request will be given the opportunity to re-establish the lock. 562 This mechanism prevents a slow client taking an excessively long time to refresh 563 an entity.</p> 564 565 566 </div> 567 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 568 <div class="directive-section"><h2><a name="CacheLockPath" id="CacheLockPath">CacheLockPath</a> <a name="cachelockpath" id="cachelockpath">Directive</a></h2> 569 <table class="directive"> 570 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the lock path directory.</td></tr> 571 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockPath <var>directory</var></code></td></tr> 572 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockPath /tmp/mod_cache-lock</code></td></tr> 573 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 574 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 575 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 576 </table> 577 <p>The <code class="directive">CacheLockPath</code> directive allows you to specify the 578 directory in which the locks are created. By default, the system's temporary 579 folder is used. Locks consist of empty files that only exist for stale URLs 580 in flight, so is significantly less resource intensive than the traditional 581 disk cache.</p> 582 583 584 </div> 585 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 586 <div class="directive-section"><h2><a name="CacheMaxExpire" id="CacheMaxExpire">CacheMaxExpire</a> <a name="cachemaxexpire" id="cachemaxexpire">Directive</a></h2> 587 <table class="directive"> 588 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum time in seconds to cache a document</td></tr> 589 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMaxExpire <var>seconds</var></code></td></tr> 590 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMaxExpire 86400 (one day)</code></td></tr> 591 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 592 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 593 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 594 </table> 595 <p>The <code class="directive">CacheMaxExpire</code> directive specifies the maximum number of 596 seconds for which cachable HTTP documents will be retained without checking the origin 597 server. Thus, documents will be out of date at most this number of seconds. This maximum 598 value is enforced even if an expiry date was supplied with the document.</p> 599 600 <div class="example"><p><code> 601 CacheMaxExpire 604800 602 </code></p></div> 603 604 </div> 605 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 606 <div class="directive-section"><h2><a name="CacheStoreNoStore" id="CacheStoreNoStore">CacheStoreNoStore</a> <a name="cachestorenostore" id="cachestorenostore">Directive</a></h2> 607 <table class="directive"> 608 <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> 609 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStoreNoStore On|Off</code></td></tr> 610 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStoreNoStore Off</code></td></tr> 611 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 612 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 613 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 614 </table> 615 <p>Ordinarily, requests or responses with Cache-Control: no-store header 616 values will not be stored in the cache. The 617 <code class="directive">CacheStoreNoStore</code> directive allows this 618 behavior to be overridden. <code class="directive">CacheStoreNoStore</code> On 619 tells the server to attempt to cache the resource even if it contains 620 no-store header values. Resources requiring authorization will 621 <em>never</em> be cached.</p> 622 623 <div class="example"><p><code> 624 CacheStoreNoStore On 625 </code></p></div> 626 627 <div class="warning"><h3>Warning:</h3> 628 As described in RFC 2616, the no-store directive is intended to 629 "prevent the inadvertent release or retention of sensitive information 630 (for example, on backup tapes)." Enabling this option could store 631 sensitive information in the cache. You are hereby warned. 632 </div> 633 634 <h3>See also</h3> 635 <ul> 636 <li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li> 637 <li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li> 638 </ul> 639 </div> 640 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> 641 <div class="directive-section"><h2><a name="CacheStorePrivate" id="CacheStorePrivate">CacheStorePrivate</a> <a name="cachestoreprivate" id="cachestoreprivate">Directive</a></h2> 642 <table class="directive"> 643 <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> 644 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStorePrivate On|Off</code></td></tr> 645 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStorePrivate Off</code></td></tr> 646 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> 647 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> 648 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> 649 </table> 650 <p>Ordinarily, responses with Cache-Control: private header values will not 651 be stored in the cache. The <code class="directive">CacheStorePrivate</code> 652 directive allows this behavior to be overridden. 653 <code class="directive">CacheStorePrivate</code> On 654 tells the server to attempt to cache the resource even if it contains 655 private header values. Resources requiring authorization will 656 <em>never</em> be cached.</p> 657 658 <div class="example"><p><code> 659 CacheStorePrivate On 660 </code></p></div> 661 662 <div class="warning"><h3>Warning:</h3> 663 This directive will allow caching even if the upstream server has 664 requested that the resource not be cached. This directive is only 665 ideal for a 'private' cache. 666 </div> 667 668 <h3>See also</h3> 669 <ul> 670 <li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li> 671 <li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li> 672 </ul> 673 </div> 674 </div> 675 <div class="bottomlang"> 676 <p><span>Available Languages: </span><a href="../en/mod/mod_cache.html" title="English"> en </a> | 677 <a href="../ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | 678 <a href="../ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p> 679 </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. 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