<modulesynopsis metafile="mod_cache.xml.meta">
<name>mod_cache</name>
-<description>Content cache keyed to URIs.</description>
+<description>RFC 2616 compliant HTTP caching filter.</description>
<status>Extension</status>
<sourcefile>mod_cache.c</sourcefile>
<identifier>cache_module</identifier>
<summary>
<note type="warning">This module should be used with care, as when the
<directive module="mod_cache">CacheQuickHandler</directive> directive is
- in its default value of <strong>on</strong>, the <directive
- module="mod_authz_host">Allow</directive> and <directive
- module="mod_authz_host">Deny</directive> directives will be circumvented.
+ in its default value of <strong>on</strong>, the <directive
+ module="mod_access_compat">Allow</directive> and <directive
+ module="mod_access_compat">Deny</directive> directives will be circumvented.
You should not enable quick handler caching for any content to which you
wish to limit access by client host name, address or environment
- variable.</note>
+ variable.</note>
<p><module>mod_cache</module> implements an <a
- href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a> compliant HTTP
- content cache that can be used to cache either local or proxied content.
- <module>mod_cache</module> requires the services of one or more storage
- management modules. One storage management module is included in
+ href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a> compliant
+ <strong>HTTP content caching filter</strong>, with support for the caching
+ of content negotiated responses containing the Vary header.</p>
+
+ <p>RFC 2616 compliant caching provides a mechanism to verify whether
+ stale or expired content is still fresh, and can represent a significant
+ performance boost when the origin server supports <strong>conditional
+ requests</strong> by honouring the
+ <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26">If-None-Match</a>
+ HTTP request header. Content is only regenerated from scratch when the content
+ has changed, and not when the cached entry expires.</p>
+
+ <p>As a filter, <module>mod_cache</module> can be placed in front of
+ content originating from any handler, including <strong>flat
+ files</strong> (served from a slow disk cached on a fast disk), the output
+ of a <strong>CGI script</strong> or <strong>dynamic content
+ generator</strong>, or content <strong>proxied from another
+ server</strong>.</p>
+
+ <p>In the default configuration, <module>mod_cache</module> inserts the
+ caching filter as far forward as possible within the filter stack,
+ utilising the <strong>quick handler</strong> to bypass all per request
+ processing when returning content to the client. In this mode of
+ operation, <module>mod_cache</module> may be thought of as a caching
+ proxy server bolted to the front of the webserver, while running within
+ the webserver itself.</p>
+
+ <p>When the quick handler is switched off using the
+ <directive module="mod_cache">CacheQuickHandler</directive> directive,
+ it becomes possible to insert the <strong>CACHE</strong> filter at a
+ point in the filter stack chosen by the administrator. This provides the
+ opportunity to cache content before that content is personalised by the
+ <module>mod_include</module> filter, or optionally compressed by the
+ <module>mod_deflate</module> filter.</p>
+
+ <p>Under normal operation, <module>mod_cache</module> will respond to
+ and can be controlled by the
+ <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9">Cache-Control</a>
+ and
+ <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.32">Pragma</a>
+ headers sent from a client in a request, or from a
+ server within a response. Under exceptional circumstances,
+ <module>mod_cache</module> can be configured to override these headers
+ and force site specific behaviour, however such behaviour will be limited
+ to this cache only, and will not affect the operation of other caches
+ that may exist between the client and server, and as a result is not
+ recommended unless strictly necessary.</p>
+
+ <p>RFC 2616 allows for the cache to return stale data while the existing
+ stale entry is refreshed from the origin server, and this is supported
+ by <module>mod_cache</module> when the
+ <directive module="mod_cache">CacheLock</directive> directive is suitably
+ configured. Such responses will contain a
+ <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.46">Warning</a>
+ HTTP header with a 110 response code. RFC 2616 also allows a cache to return
+ stale data when the attempt made to refresh the stale data returns an
+ error 500 or above, and this behaviour is supported by default by
+ <module>mod_cache</module>. Such responses will contain a
+ <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.46">Warning</a>
+ HTTP header with a 111 response code.</p>
+
+ <p><module>mod_cache</module> requires the services of one or more
+ storage management modules. The following storage management modules are included in
the base Apache distribution:</p>
<dl>
- <dt><module>mod_disk_cache</module></dt>
- <dd>implements a disk based storage manager.</dd>
+ <dt><module>mod_cache_disk</module></dt>
+ <dd>Implements a disk based storage manager. Headers and bodies are
+ stored separately on disk, in a directory structure derived from the
+ md5 hash of the cached URL. Multiple content negotiated responses can
+ be stored concurrently, however the caching of partial content is not
+ supported by this module. The <program>htcacheclean</program> tool is
+ provided to list cached URLs, remove cached URLs, or to maintain the size
+ of the disk cache within size and inode limits.</dd>
+ <dt><module>mod_cache_socache</module></dt>
+ <dd>Implements a shared object cache based storage manager. Headers and
+ bodies are stored together beneath a single key based on the URL of the
+ response being cached. Multiple content negotiated responses can
+ be stored concurrently, however the caching of partial content is not
+ supported by this module.</dd>
</dl>
- <p>Content is stored in and retrieved from the cache using URI based keys. Content with
- access protection is not cached.</p>
<p>Further details, discussion, and examples, are provided in the
<a href="../caching.html">Caching Guide</a>.</p>
</summary>
<section id="related"><title>Related Modules and Directives</title>
<related>
<modulelist>
- <module>mod_disk_cache</module>
+ <module>mod_cache_disk</module>
+ <module>mod_cache_socache</module>
</modulelist>
<directivelist>
- <directive module="mod_disk_cache">CacheRoot</directive>
- <directive module="mod_disk_cache">CacheDirLevels</directive>
- <directive module="mod_disk_cache">CacheDirLength</directive>
- <directive module="mod_disk_cache">CacheMinFileSize</directive>
- <directive module="mod_disk_cache">CacheMaxFileSize</directive>
+ <directive module="mod_cache_disk">CacheRoot</directive>
+ <directive module="mod_cache_disk">CacheDirLevels</directive>
+ <directive module="mod_cache_disk">CacheDirLength</directive>
+ <directive module="mod_cache_disk">CacheMinFileSize</directive>
+ <directive module="mod_cache_disk">CacheMaxFileSize</directive>
+ <directive module="mod_cache_socache">CacheSocache</directive>
+ <directive module="mod_cache_socache">CacheSocacheMaxTime</directive>
+ <directive module="mod_cache_socache">CacheSocacheMinTime</directive>
+ <directive module="mod_cache_socache">CacheSocacheMaxSize</directive>
+ <directive module="mod_cache_socache">CacheSocacheReadSize</directive>
+ <directive module="mod_cache_socache">CacheSocacheReadTime</directive>
</directivelist>
</related>
</section>
<section id="sampleconf"><title>Sample Configuration</title>
<example><title>Sample httpd.conf</title>
- #<br />
- # Sample Cache Configuration<br />
- #<br />
- LoadModule cache_module modules/mod_cache.so<br />
- <br />
- <IfModule mod_cache.c><br />
- <indent>
- LoadModule disk_cache_module modules/mod_disk_cache.so<br />
- <IfModule mod_disk_cache.c><br />
- <indent>
- CacheRoot c:/cacheroot<br />
- CacheEnable disk /<br />
- CacheDirLevels 5<br />
- CacheDirLength 3<br />
- </indent>
- </IfModule> <br />
- <br />
- # When acting as a proxy, don't cache the list of security updates<br />
- CacheDisable http://security.update.server/update-list/<br />
- </indent>
- </IfModule>
+ <highlight language="config">
+#
+# Sample Cache Configuration
+#
+LoadModule cache_module modules/mod_cache.so
+<IfModule mod_cache.c>
+ LoadModule cache_disk_module modules/mod_cache_disk.so
+ <IfModule mod_cache_disk.c>
+ CacheRoot c:/cacheroot
+ CacheEnable disk /
+ CacheDirLevels 5
+ CacheDirLength 3
+ </IfModule>
+
+ # When acting as a proxy, don't cache the list of security updates
+ CacheDisable http://security.update.server/update-list/
+</IfModule>
+ </highlight>
</example>
</section>
becomes stale, and the time the stale entity is fully refreshed. On a busy
server, a significant number of requests might arrive during this time, and
cause a <strong>thundering herd</strong> of requests to strike the backend
- suddenly and unpredicably.</p>
+ suddenly and unpredictably.</p>
<p>To keep the thundering herd at bay, the <directive>CacheLock</directive>
directive can be used to define a directory in which locks are created for
URLs <strong>in flight</strong>. The lock is used as a <strong>hint</strong>
<section>
<title>Example configuration</title>
<example><title>Enabling the cache lock</title>
- #<br />
- # Enable the cache lock<br />
- #<br />
- <IfModule mod_cache.c><br />
- <indent>
- CacheLock on<br />
- CacheLockPath /tmp/mod_cache-lock<br />
- CacheLockMaxAge 5<br />
- </indent>
- </IfModule>
+ <highlight language="config">
+#
+# Enable the cache lock
+#
+<IfModule mod_cache.c>
+ CacheLock on
+ CacheLockPath /tmp/mod_cache-lock
+ CacheLockMaxAge 5
+</IfModule>
+ </highlight>
</example>
</section>
</section>
<p>Under the default mode of cache operation, the cache runs as a quick handler,
short circuiting the majority of server processing and offering the highest
cache performance available.</p>
-
+
<p>In this mode, the cache <strong>bolts onto</strong> the front of the server,
- acting as if a free standing RFC2616 caching proxy had been placed in front of
+ acting as if a free standing RFC 2616 caching proxy had been placed in front of
the server.</p>
-
+
<p>While this mode offers the best performance, the administrator may find that
under certain circumstances they may want to perform further processing on the
request after the request is cached, such as to inject personalisation into the
- cached page, or to apply authorisation restrictions to the content. Under these
+ cached page, or to apply authorization restrictions to the content. Under these
circumstances, an administrator is often forced to place independent reverse
proxy servers either behind or in front of the caching server to achieve this.</p>
<p>To solve this problem the <directive module="mod_cache">CacheQuickHandler
</directive> directive can be set to <strong>off</strong>, and the server will
process all phases normally handled by a non-cached request, including the
- <strong>authentication and authorisation</strong> phases.</p>
+ <strong>authentication and authorization</strong> phases.</p>
<p>In addition, the administrator may optionally specify the <strong>precise point
within the filter chain</strong> where caching is to take place by adding the
place the <strong>CACHE</strong> filter before the <strong>DEFLATE</strong>
filter as in the example below:</p>
- <example>
- # Cache content before optional compression<br />
- CacheQuickHandler off<br />
- AddOutputFilterByType CACHE;DEFLATE text/plain<br /><br />
- </example>
+ <highlight language="config">
+# Cache content before optional compression
+CacheQuickHandler off
+AddOutputFilterByType CACHE;DEFLATE text/plain
+ </highlight>
<p>Another option is to have content cached before personalisation is applied
by <module>mod_include</module> (or another content processing filter). In this
example templates containing tags understood by
<module>mod_include</module> are cached before being parsed:</p>
- <example>
- # Cache content before mod_include and mod_deflate<br />
- CacheQuickHandler off<br />
- AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html<br /><br />
- </example>
+ <highlight language="config">
+# Cache content before mod_include and mod_deflate
+CacheQuickHandler off
+AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html
+ </highlight>
<p>You may place the <strong>CACHE</strong> filter anywhere you wish within the
filter chain. In this example, content is cached after being parsed by
<module>mod_include</module>, but before being processed by
<module>mod_deflate</module>:</p>
- <example>
- # Cache content between mod_include and mod_deflate<br />
- CacheQuickHandler off<br />
- AddOutputFilterByType INCLUDES;CACHE;DEFLATE text/html<br /><br />
- </example>
+ <highlight language="config">
+# Cache content between mod_include and mod_deflate
+CacheQuickHandler off
+AddOutputFilterByType INCLUDES;CACHE;DEFLATE text/html
+ </highlight>
<note type="warning"><title>Warning:</title>If the location of the
<strong>CACHE</strong> filter in the filter chain is changed for any reason,
<directive module="mod_log_config">LogFormat</directive> directive as
follows:</p>
- <example>
+ <highlight language="config">
LogFormat "%{cache-status}e ..."
- </example>
+ </highlight>
<p>Based on the caching decision made, the reason is also written to the
- subprocess environment under one the following three keys, as appropriate:</p>
+ subprocess environment under one the following four keys, as appropriate:</p>
<dl>
<dt>cache-hit</dt><dd>The response was served from cache.</dd>
<dt>cache-revalidate</dt><dd>The response was stale and was successfully
revalidated, then served from cache.</dd>
<dt>cache-miss</dt><dd>The response was served from the upstream server.</dd>
+ <dt>cache-invalidate</dt><dd>The cached entity was invalidated by a request
+ method other than GET or HEAD.</dd>
</dl>
<p>This makes it possible to support conditional logging of cached requests
as per the following example:</p>
- <example>
- CustomLog cached-requests.log common env=cache-hit<br />
- CustomLog uncached-requests.log common env=cache-miss<br />
- CustomLog revalidated-requests.log common env=cache-revalidate<br />
- </example>
+ <highlight language="config">
+CustomLog "cached-requests.log" common env=cache-hit
+CustomLog "uncached-requests.log" common env=cache-miss
+CustomLog "revalidated-requests.log" common env=cache-revalidate
+CustomLog "invalidated-requests.log" common env=cache-invalidate
+ </highlight>
+ <p>For module authors, a hook called <var>cache_status</var> is available,
+ allowing modules to respond to the caching outcomes above in customised
+ ways.</p>
</section>
-
+
<directivesynopsis>
<name>CacheEnable</name>
<description>Enable caching of specified URLs using a specified storage
manager</description>
-<syntax>CacheEnable <var>cache_type</var> <var>url-string</var></syntax>
+<syntax>CacheEnable <var>cache_type</var> [<var>url-string</var>]</syntax>
<contextlist><context>server config</context><context>virtual host</context>
+<context>directory</context>
</contextlist>
+<compatibility>A url-string of '/' applied to forward proxy content in 2.2 and
+ earlier.</compatibility>
<usage>
<p>The <directive>CacheEnable</directive> directive instructs
<module>mod_cache</module> to cache urls at or below
<var>url-string</var>. The cache storage manager is specified with the
- <var>cache_type</var> argument. If the <directive>CacheEnable</directive>
- directive is placed inside a <directive type="section">Location</directive>
- directive, the <var>url-string</var> becomes optional.
+ <var>cache_type</var> argument. The <directive>CacheEnable</directive>
+ directive can alternatively be placed inside either
+ <directive type="section">Location</directive> or
+ <directive type="section">LocationMatch</directive> sections to indicate
+ the content is cacheable.
<var>cache_type</var> <code>disk</code> instructs
<module>mod_cache</module> to use the disk based storage manager
- implemented by <module>mod_disk_cache</module>.</p>
+ implemented by <module>mod_cache_disk</module>. <var>cache_type</var>
+ <code>socache</code> instructs <module>mod_cache</module> to use the
+ shared object cache based storage manager implemented by
+ <module>mod_cache_socache</module>.</p>
<p>In the event that the URL space overlaps between different
<directive>CacheEnable</directive> directives (as in the example below),
each possible storage manager will be run until the first one that
actually processes the request. The order in which the storage managers are
run is determined by the order of the <directive>CacheEnable</directive>
- directives in the configuration file.</p>
-
- <p>When acting as a forward proxy server, <var>url-string</var> can
- also be used to specify remote sites and proxy protocols which
- caching should be enabled for.</p>
-
- <example>
- # Cache proxied url's<br />
- CacheEnable disk /<br /><br />
- # Cache FTP-proxied url's<br />
- CacheEnable disk ftp://<br /><br />
- # Cache content from www.apache.org<br />
- CacheEnable disk http://www.apache.org/<br />
- </example>
+ directives in the configuration file. <directive>CacheEnable</directive>
+ directives within <directive type="section">Location</directive> or
+ <directive type="section">LocationMatch</directive> sections are processed
+ before globally defined <directive>CacheEnable</directive> directives.</p>
+
+ <p>When acting as a forward proxy server, <var>url-string</var> must
+ minimally begin with a protocol for which caching should be enabled.</p>
+
+ <highlight language="config">
+# Cache content (normal handler only)
+CacheQuickHandler off
+<Location "/foo">
+ CacheEnable disk
+</Location>
+
+# Cache regex (normal handler only)
+CacheQuickHandler off
+<LocationMatch "foo$">
+ CacheEnable disk
+</LocationMatch>
+
+# Cache all but forward proxy url's (normal or quick handler)
+CacheEnable disk /
+
+# Cache FTP-proxied url's (normal or quick handler)
+CacheEnable disk ftp://
+
+# Cache forward proxy content from www.example.org (normal or quick handler)
+CacheEnable disk http://www.example.org/
+ </highlight>
<p>A hostname starting with a <strong>"*"</strong> matches all hostnames with
that suffix. A hostname starting with <strong>"."</strong> matches all
hostnames containing the domain components that follow.</p>
- <example>
- # Match www.apache.org, and fooapache.org<br />
- CacheEnable disk http://*apache.org/<br />
- # Match www.apache.org, but not fooapache.org<br />
- CacheEnable disk http://.apache.org/<br />
- </example>
+ <highlight language="config">
+# Match www.example.org, and fooexample.org
+CacheEnable disk http://*example.org/
+# Match www.example.org, but not fooexample.org
+CacheEnable disk http://.example.org/
+ </highlight>
- <p> The <code>no-cache</code> environment variable can be set to
+ <p> The <code>no-cache</code> environment variable can be set to
disable caching on a finer grained set of resources in versions
2.2.12 and later.</p>
<description>Disable caching of specified URLs</description>
<syntax>CacheDisable <var>url-string</var> | <var>on</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
+<context>directory</context><context>.htaccess</context>
</contextlist>
<usage>
<var>url-string</var>.</p>
<example><title>Example</title>
+ <highlight language="config">
CacheDisable /local_files
+ </highlight>
</example>
<p>If used in a <directive type="section">Location</directive> directive,
is used, caching for the whole location will be disabled.</p>
<example><title>Example</title>
- <Location /foo><br />
- CacheDisable on<br />
- </Location><br />
+ <highlight language="config">
+<Location "/foo">
+ CacheDisable on
+</Location>
+ </highlight>
</example>
- <p> The <code>no-cache</code> environment variable can be set to
+ <p>The <code>no-cache</code> environment variable can be set to
disable caching on a finer grained set of resources in versions
2.2.12 and later.</p>
<usage>
<p>The <directive>CacheMaxExpire</directive> directive specifies the maximum number of
- seconds for which cachable HTTP documents will be retained without checking the origin
+ seconds for which cacheable HTTP documents will be retained without checking the origin
server. Thus, documents will be out of date at most this number of seconds. This maximum
value is enforced even if an expiry date was supplied with the document.</p>
- <example>
+ <highlight language="config">
CacheMaxExpire 604800
- </example>
+ </highlight>
</usage>
</directivesynopsis>
<usage>
<p>The <directive>CacheMinExpire</directive> directive specifies the minimum number of
- seconds for which cachable HTTP documents will be retained without checking the origin
+ seconds for which cacheable HTTP documents will be retained without checking the origin
server. This is only used if no valid expire time was supplied with the document.</p>
- <example>
+ <highlight language="config">
CacheMinExpire 3600
- </example>
+ </highlight>
</usage>
</directivesynopsis>
with the document. The value specified with the <directive>CacheMaxExpire</directive>
directive does <em>not</em> override this setting.</p>
- <example>
+ <highlight language="config">
CacheDefaultExpire 86400
- </example>
+ </highlight>
</usage>
</directivesynopsis>
<context>directory</context>
<context>.htaccess</context>
</contextlist>
-
+
<usage>
<p>Ordinarily, documents without a last-modified date are not cached.
Under some circumstances the last-modified date is removed (during
<directive>CacheDefaultExpire</directive> directive will be used to
generate an expiration date.</p>
- <example>
+ <highlight language="config">
CacheIgnoreNoLastMod On
- </example>
+ </highlight>
</usage>
</directivesynopsis>
<directive>CacheIgnoreCacheControl</directive> directive allows this
behavior to be overridden. <directive>CacheIgnoreCacheControl On</directive>
tells the server to attempt to serve the resource from the cache even
- if the request contains no-cache header values. Resources requiring
- authorization will <em>never</em> be cached.</p>
+ if the request contains no-cache header values.</p>
- <example>
+ <highlight language="config">
CacheIgnoreCacheControl On
- </example>
+ </highlight>
<note type="warning"><title>Warning:</title>
This directive will allow serving from the cache even if the client has
<usage>
<p>Ordinarily, requests with query string parameters are cached separately
for each unique query string. This is according to RFC 2616/13.9 done only
- if an expiration time is specified. The
+ if an expiration time is specified. The
<directive>CacheIgnoreQueryString</directive> directive tells the cache to
- cache requests even if no expiration time is specified, and to reply with
+ cache requests even if no expiration time is specified, and to reply with
a cached reply even if the query string differs. From a caching point of
- view the request is treated as if having no query string when this
+ view the request is treated as if having no query string when this
directive is enabled.</p>
- <example>
+ <highlight language="config">
CacheIgnoreQueryString On
- </example>
+ </highlight>
</usage>
</directivesynopsis>
<context>directory</context>
<context>.htaccess</context>
</contextlist>
-
+
<usage>
<p>In the event that a document does not provide an expiry date but does
provide a last-modified date, an expiry date can be calculated based on
<directive>CacheMaxExpire</directive>, then the latter takes
precedence.</p>
- <example>
+ <highlight language="config">
CacheLastModifiedFactor 0.5
- </example>
+ </highlight>
</usage>
</directivesynopsis>
<code>None</code>.</p>
<example><title>Example 1</title>
+ <highlight language="config">
CacheIgnoreHeaders Set-Cookie
+ </highlight>
</example>
<example><title>Example 2</title>
+ <highlight language="config">
CacheIgnoreHeaders None
+ </highlight>
</example>
<note type="warning"><title>Warning:</title>
<li><code>/someapplication/image.gif;jsessionid=123456789</code></li>
<li><code>/someapplication/image.gif?PHPSESSIONID=12345678</code></li>
</ul>
- <p>This causes cachable resources to be stored separately for each session, which
+ <p>This causes cacheable resources to be stored separately for each session, which
is often not desired. <directive>CacheIgnoreURLSessionIdentifiers</directive> lets
define a list of identifiers that are removed from the key that is used to identify
- an entity in the cache, such that cachable resources are not stored separately for
+ an entity in the cache, such that cacheable resources are not stored separately for
each session.
</p>
<p><code>CacheIgnoreURLSessionIdentifiers None</code> clears the list of ignored
identifiers. Otherwise, each identifier is added to the list.</p>
<example><title>Example 1</title>
+ <highlight language="config">
CacheIgnoreURLSessionIdentifiers jsessionid
+ </highlight>
</example>
<example><title>Example 2</title>
+ <highlight language="config">
CacheIgnoreURLSessionIdentifiers None
+ </highlight>
</example>
</usage>
the origin server, and the response may be fulfilled from cache
if the backend resource has not changed.</p>
- <example>
+ <highlight language="config">
CacheStoreExpired On
- </example>
+ </highlight>
</usage>
</directivesynopsis>
directive allows this behavior to be overridden.
<directive>CacheStorePrivate</directive> On
tells the server to attempt to cache the resource even if it contains
- private header values. Resources requiring authorization will
- <em>never</em> be cached.</p>
+ private header values.</p>
- <example>
+ <highlight language="config">
CacheStorePrivate On
- </example>
+ </highlight>
<note type="warning"><title>Warning:</title>
This directive will allow caching even if the upstream server has
<usage>
<p>Ordinarily, requests or responses with Cache-Control: no-store header
values will not be stored in the cache. The
- <directive>CacheStoreNoCache</directive> directive allows this
- behavior to be overridden. <directive>CacheStoreNoCache</directive> On
+ <directive>CacheStoreNoStore</directive> directive allows this
+ behavior to be overridden. <directive>CacheStoreNoStore</directive> On
tells the server to attempt to cache the resource even if it contains
- no-store header values. Resources requiring authorization will
- <em>never</em> be cached.</p>
+ no-store header values.</p>
- <example>
+ <highlight language="config">
CacheStoreNoStore On
- </example>
+ </highlight>
<note type="warning"><title>Warning:</title>
As described in RFC 2616, the no-store directive is intended to
<default>CacheLock off</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
-<compatibility>Available in Apache 2.2.15 and later</compatibility>
<usage>
<p>The <directive>CacheLock</directive> directive enables the thundering herd lock
for the given URL space.</p>
-
+
<p>In a minimal configuration the following directive is all that is needed to
- enable the thundering herd lock in the default system temp directory.</p>
+ enable the thundering herd lock in the default run-time file directory.</p>
- <example>
- # Enable cache lock<br />
- CacheLock on<br /><br />
- </example>
+ <highlight language="config">
+# Enable cache lock
+CacheLock on
+ </highlight>
+ <p>Locks consist of empty files that only exist for stale URLs in flight, so this
+ is significantly less resource intensive than the traditional disk cache.</p>
</usage>
</directivesynopsis>
<name>CacheLockPath</name>
<description>Set the lock path directory.</description>
<syntax>CacheLockPath <var>directory</var></syntax>
-<default>CacheLockPath /tmp/mod_cache-lock</default>
+<default>CacheLockPath mod_cache-lock</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
-
+
<usage>
<p>The <directive>CacheLockPath</directive> directive allows you to specify the
- directory in which the locks are created. By default, the system's temporary
- folder is used. Locks consist of empty files that only exist for stale URLs
- in flight, so is significantly less resource intensive than the traditional
- disk cache.</p>
-
+ directory in which the locks are created. If <var>directory</var> is not an absolute
+ path, the location specified will be relative to the value of
+ <directive module="core">DefaultRuntimeDir</directive>.</p>
</usage>
</directivesynopsis>
<default>CacheLockMaxAge 5</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
-
+
<usage>
<p>The <directive>CacheLockMaxAge</directive> directive specifies the maximum
age of any cache lock.</p>
-
+
<p>A lock older than this value in seconds will be ignored, and the next
incoming request will be given the opportunity to re-establish the lock.
This mechanism prevents a slow client taking an excessively long time to refresh
an entity.</p>
-
+
</usage>
</directivesynopsis>
<default>CacheQuickHandler on</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
+ <compatibility>Apache HTTP Server 2.3.3 and later</compatibility>
<usage>
<p>The <directive module="mod_cache">CacheQuickHandler</directive> directive
<p>When disabled, the cache operates as a normal handler, and is subject to
the full set of phases when handling a server request. While this mode is
slower than the default, it allows the cache to be used in cases where full
- processing is required, such as when content is subject to authorisation.</p>
+ processing is required, such as when content is subject to authorization.</p>
- <example>
- # Run cache as a normal handler<br />
- CacheQuickHandler off<br /><br />
- </example>
+ <highlight language="config">
+# Run cache as a normal handler
+CacheQuickHandler off
+ </highlight>
<p>It is also possible, when the quick handler is disabled, for the
administrator to choose the precise location within the filter chain where
caching is to be performed, by adding the <strong>CACHE</strong> filter to
the chain.</p>
- <example>
- # Cache content before mod_include and mod_deflate<br />
- CacheQuickHandler off<br />
- AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html<br /><br />
- </example>
+ <highlight language="config">
+# Cache content before mod_include and mod_deflate
+CacheQuickHandler off
+AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html
+ </highlight>
<p>If the CACHE filter is specified more than once, the last instance will
apply.</p>
<context>.htaccess</context>
</contextlist>
<compatibility>Available in Apache 2.3.9 and later</compatibility>
-
+
<usage>
<p>When the <directive module="mod_cache">CacheHeader</directive> directive
is switched on, an <strong>X-Cache</strong> header will be added to the response
with the cache status of this response. If the normal handler is used, this
- directive may appear within a <directive module="core"><Directory></directive>
- or <directive module="core"><Location></directive> directive. If the quick
+ directive may appear within a <directive type="section" module="core">Directory</directive>
+ or <directive type="section" module="core">Location</directive> directive. If the quick
handler is used, this directive must appear within a server or virtual host
context, otherwise the setting will be ignored.</p>
server and was not served from cache.</dd>
</dl>
- <example>
- # Enable the X-Cache header<br />
- CacheHeader on<br />
- </example>
+ <highlight language="config">
+# Enable the X-Cache header
+CacheHeader on
+ </highlight>
- <example>
- X-Cache: HIT from localhost<br />
- </example>
+ <highlight language="config">
+ X-Cache: HIT from localhost
+ </highlight>
</usage>
</directivesynopsis>
<context>.htaccess</context>
</contextlist>
<compatibility>Available in Apache 2.3.9 and later</compatibility>
-
+
<usage>
<p>When the <directive module="mod_cache">CacheDetailHeader</directive> directive
is switched on, an <strong>X-Cache-Detail</strong> header will be added to the response
containing the detailed reason for a particular caching decision.</p>
-
+
<p>It can be useful during development of cached RESTful services to have additional
information about the caching decision written to the response headers, so as to
confirm whether <code>Cache-Control</code> and other headers have been correctly
used by the service and client.</p>
-
+
<p>If the normal handler is used, this directive may appear within a
- <directive module="core"><Directory></directive> or
- <directive module="core"><Location></directive> directive. If the quick handler
+ <directive type="section" module="core">Directory</directive> or
+ <directive type="section" module="core">Location</directive> directive. If the quick handler
is used, this directive must appear within a server or virtual host context, otherwise
the setting will be ignored.</p>
- <example>
- # Enable the X-Cache-Detail header<br />
- CacheDetailHeader on<br />
- </example>
+ <highlight language="config">
+# Enable the X-Cache-Detail header
+CacheDetailHeader on
+ </highlight>
<example>
X-Cache-Detail: "conditional cache hit: entity refreshed" from localhost<br />
should be cached beneath the same cache key, a new base URL can be specified
with this directive.</p>
- <example>
- # Override the base URL of the cache key.<br />
- CacheKeyBaseURL http://www.example.com/<br />
- </example>
+ <highlight language="config">
+# Override the base URL of the cache key.
+CacheKeyBaseURL http://www.example.com/
+ </highlight>
<note type="warning">Take care when setting this directive. If two separate virtual
hosts are accidentally given the same base URL, entries from one virtual host
</usage>
</directivesynopsis>
+<directivesynopsis>
+<name>CacheStaleOnError</name>
+<description>Serve stale content in place of 5xx responses.</description>
+<syntax>CacheStaleOnError <var>on|off</var></syntax>
+<default>CacheStaleOnError on</default>
+<contextlist><context>server config</context>
+ <context>virtual host</context>
+ <context>directory</context>
+ <context>.htaccess</context>
+</contextlist>
+<compatibility>Available in Apache 2.3.9 and later</compatibility>
+
+<usage>
+ <p>When the <directive module="mod_cache">CacheStaleOnError</directive> directive
+ is switched on, and when stale data is available in the cache, the cache will
+ respond to 5xx responses from the backend by returning the stale data instead of
+ the 5xx response. While the Cache-Control headers sent by clients will be respected,
+ and the raw 5xx responses returned to the client on request, the 5xx response so
+ returned to the client will not invalidate the content in the cache.</p>
+
+ <highlight language="config">
+# Serve stale data on error.
+CacheStaleOnError on
+ </highlight>
+
+</usage>
+</directivesynopsis>
+
</modulesynopsis>
projects / apache / blobdiff