Apache Module mod_cache

Available Languages: en | + ko

+ + + +

Description:	Content cache keyed to URIs.
Status:	Experimental
Module Identifier:	cache_module
Source File:	mod_cache.c

Summary

+ +

+ This module is experimental. Documentation is still under development... +

+ +

mod_cache implements an RFC 2616 compliant HTTP + content cache that can be used to cache either local or proxied content. + mod_cache requires the services of one or more storage + management modules. Two storage management modules are included in + the base Apache distribution:

mod_disk_cache: implements a disk based storage manager.
mod_mem_cache: implements a memory based storage manager. + mod_mem_cache can be configured to operate in two + modes: caching open file descriptors or caching objects in heap storage. + mod_mem_cache can be used to cache locally generated content + or to cache backend server content for mod_proxy when + configured using ProxyPass + (aka reverse proxy)

+ +

Content is stored in and retrieved from the cache using URI based keys. Content with + access protection is not cached.

Topics

Related Modules and Directives
Sample Configuration

Related Modules and Directives

Related Modules	Related Directives
`mod_disk_cache` `mod_mem_cache`	`CacheRoot` `CacheSize` `CacheGcInterval` `CacheDirLevels` `CacheDirLength` `CacheExpiryCheck` `CacheMinFileSize` `CacheMaxFileSize` `CacheTimeMargin` `CacheGcDaily` `CacheGcUnused` `CacheGcClean` `CacheGcMemUsage` `MCacheSize` `MCacheMaxObjectCount` `MCacheMinObjectSize` `MCacheMaxObjectSize` `MCacheRemovalAlgorithm` `MCacheMaxStreamingBuffer`

Sample Configuration

Sample httpd.conf

+ # + # Sample Cache Configuration + # + LoadModule cache_module modules/mod_cache.so + + <IfModule mod_cache.c> + + #LoadModule disk_cache_module modules/mod_disk_cache.so + <IfModule mod_disk_cache.c> + + CacheRoot c:/cacheroot + CacheSize 256 + CacheEnable disk / + CacheDirLevels 5 + CacheDirLength 3 + + </IfModule> + + LoadModule mem_cache_module modules/mod_mem_cache.so + <IfModule mod_mem_cache.c> + + CacheEnable mem / + MCacheSize 4096 + MCacheMaxObjectCount 100 + MCacheMinObjectSize 1 + MCacheMaxObjectSize 2048 + + </IfModule> + + </IfModule> +

CacheDefaultExpire Directive

+ + + + + + + +

Description:	The default duration to cache a document when no expiry date is specified.
Syntax:	`CacheDefaultExpire seconds`
Default:	`CacheDefaultExpire 3600 (one hour)`
Context:	server config, virtual host
Status:	Experimental
Module:	mod_cache

The CacheDefaultExpire directive specifies a default time, + in seconds, to cache a document if neither an expiry date nor last-modified date are provided + with the document. The value specified with the CacheMaxExpire + directive does not override this setting.

+ +

+ CacheDefaultExpire 86400 +

+ +

CacheDisable Directive

+ + + + + + +

Description:	Disable caching of specified URLs
Syntax:	`CacheDisable url-string`
Context:	server config, virtual host
Status:	Experimental
Module:	mod_cache

The CacheDisable directive instructs + mod_cache to not cache urls at or below + url-string.

+ +

Example

+ CacheDisable /local_files +

+ +

CacheEnable Directive

+ + + + + + +

Description:	Enable caching of specified URLs using a specified storage +manager
Syntax:	`CacheEnable cache_type url-string`
Context:	server config, virtual host
Status:	Experimental
Module:	mod_cache

The CacheEnable directive instructs + mod_cache to cache urls at or below + url-string. The cache storage manager is specified with the + cache_type argument. cache_type mem + instructs mod_cache to use the memory based storage + manager implemented by mod_mem_cache. + cache_type disk instructs + mod_cache to use the disk based storage manager + implemented by mod_disk_cache. + cache_type fd instructs + mod_cache to use the file descriptor cache implemented + by mod_mem_cache.

In the event that the URL space overlaps between different + CacheEnable 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 CacheEnable + directives in the configuration file.

+ +

+ CacheEnable mem /manual + CacheEnable fd /images + CacheEnable disk / +

+ +

CacheForceCompletion Directive

+ + + + + + + +

Description:	Percentage of document served, after which the server +will complete caching the file even if the request is cancelled.
Syntax:	`CacheForceCompletion Percentage`
Default:	`CacheForceCompletion 60`
Context:	server config, virtual host
Status:	Experimental
Module:	mod_cache

Ordinarily, if a request is cancelled while the response is being + cached and delivered to the client the processing of the response will + stop and the cache entry will be removed. The + CacheForceCompletion directive specifies a + threshold beyond which the document will continue to be cached to + completion, even if the request is cancelled.

+ +

The threshold is a percentage specified as a value between + 1 and 100. A value of 0 + specifies that the default be used. A value of 100 + will only cache documents that are served in their entirety. A value + between 60 and 90 is recommended.

+ +

+ CacheForceCompletion 80 +

+ +

Note:

+ This feature is currently not implemented. +

+ +

CacheIgnoreCacheControl Directive

+ + + + + + + +

Description:	Ignore the fact that the client requested the content not be +cached.
Syntax:	`CacheIgnoreCacheControl On\|Off`
Default:	`CacheIgnoreCacheControl Off`
Context:	server config, virtual host
Status:	Experimental
Module:	mod_cache

Ordinarily, documents with no-cache or no-store header values will not be stored in the cache. + The CacheIgnoreCacheControl directive allows this behavior to be overridden. + CacheIgnoreCacheControl On tells the server to attempt to cache the document + even if it contains no-cache or no-store header values. Documents requiring authorization will + never be cached.

+ +

+ CacheIgnoreCacheControl On +

+ +

CacheIgnoreHeaders Directive

+ + + + + + + +

Description:	Do not store the given HTTP header(s) in the cache. +
Syntax:	`CacheIgnoreHeaders header-string [header-string] ...`
Default:	`CacheIgnoreHeaders None`
Context:	server config, virtual host
Status:	Experimental
Module:	mod_cache

According to RFC 2616, hop-by-hop HTTP headers are not stored in + the cache. The following HTTP headers are hop-by-hop headers and thus + do not get stored in the cache in any case regardless of the + setting of CacheIgnoreHeaders:

+ +

Connection
Keep-Alive
Proxy-Authenticate
Proxy-Authorization
TE
Trailers
Transfer-Encoding
Upgrade

+ +

CacheIgnoreHeaders specifies additional HTTP + headers that should not to be stored in the cache. For example, it makes + sense in some cases to prevent cookies from being stored in the cache.

+ +

CacheIgnoreHeaders takes a space separated list + of HTTP headers that should not be stored in the cache. If only hop-by-hop + headers not should be stored in the cache (the RFC 2616 compliant + behaviour), CacheIgnoreHeaders can be set to + None.

+ +

Example 1

+ CacheIgnoreHeaders Set-Cookie +

+ +

Example 2

+ CacheIgnoreHeaders None +

+ +

Warning:

+ If headers like Expires which are needed for proper cache + management are not stored due to a + CacheIgnoreHeaders setting, the behaviour of + mod_cache is undefined. +

+ +

CacheIgnoreNoLastMod Directive

+ + + + + + + +

Description:	Ignore the fact that a response has no Last Modified +header.
Syntax:	`CacheIgnoreNoLastMod On\|Off`
Default:	`CacheIgnoreNoLastMod Off`
Context:	server config, virtual host
Status:	Experimental
Module:	mod_cache

Ordinarily, documents without a last-modified date are not cached. + Under some circumstances the last-modified date is removed (during + mod_include processing for example) or not provided + at all. The CacheIgnoreNoLastMod directive + provides a way to specify that documents without last-modified dates + should be considered for caching, even without a last-modified date. + If neither a last-modified date nor an expiry date are provided with + the document then the value specified by the + CacheDefaultExpire directive will be used to + generate an expiration date.

+ +

+ CacheIgnoreNoLastMod On +

+ +

CacheLastModifiedFactor Directive

+ + + + + + + +

Description:	The factor used to compute an expiry date based on the +LastModified date.
Syntax:	`CacheLastModifiedFactor float`
Default:	`CacheLastModifiedFactor 0.1`
Context:	server config, virtual host
Status:	Experimental
Module:	mod_cache

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 + the time since the document was last modified. The + CacheLastModifiedFactor directive specifies a + factor to be used in the generation of this expiry date + according to the following formula: + + expiry-period = time-since-last-modified-date * factor + expiry-date = current-date + expiry-period + + For example, if the document was last modified 10 hours ago, and + factor is 0.1 then the expiry-period will be set to + 10*0.1 = 1 hour. If the current time was 3:00pm then the computed + expiry-date would be 3:00pm + 1hour = 4:00pm. + + If the expiry-period would be longer than that set by + CacheMaxExpire, then the latter takes + precedence.

+ +

+ CacheLastModifiedFactor 0.5 +

+ +

CacheMaxExpire Directive

+ + + + + + + +

Description:	The maximum time in seconds to cache a document
Syntax:	`CacheMaxExpire seconds`
Default:	`CacheMaxExpire 86400 (one day)`
Context:	server config, virtual host
Status:	Experimental
Module:	mod_cache

The CacheMaxExpire directive specifies the maximum number of + seconds for which cachable 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.

+ +

+ CacheMaxExpire 604800 +

+ +