Apache HTTP Server Version 2.4
Apache Module mod_cache_disk
| Description: | Disk based storage module for the HTTP caching filter. |
|---|---|
| Status: | Extension |
| Module Identifier: | cache_disk_module |
| Source File: | mod_cache_disk.c |
Summary
mod_cache_disk implements a disk based storage
manager for mod_cache.
The headers and bodies of cached responses 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 yet supported by this module.
Atomic cache updates to both header and body files are achieved without the need for locking by storing the device and inode numbers of the body file within the header file. This has the side effect that cache entries manually moved into the cache will be ignored.
The htcacheclean tool is provided to list cached
URLs, remove cached URLs, or to maintain the size of the disk cache
within size and/or inode limits. The tool can be run on demand, or
can be daemonized to offer continuous monitoring of directory sizes.
Note:
mod_cache_disk requires the services of
mod_cache, which must be
loaded before mod_cache_disk.
Note:
mod_cache_disk uses the sendfile feature to
serve files from the cache when supported by the platform, and
when enabled with EnableSendfile.
However, per-directory and .htaccess configuration of
EnableSendfile are ignored by
mod_cache_disk as the corresponding settings are not
available to the module when a request is being served from the
cache.
Bugfix checklist
See also
CacheDirLength Directive
| Description: | The number of characters in subdirectory names |
|---|---|
| Syntax: | CacheDirLength length |
| Default: | CacheDirLength 2 |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_cache_disk |
The CacheDirLength directive sets the number
of characters for each subdirectory name in the cache hierarchy. It can
be used in conjunction with CacheDirLevels to
determine the approximate structure of your cache hierarchy.
A high value for CacheDirLength combined
with a low value for CacheDirLevels will result in
a relatively flat hierarchy, with a large number of subdirectories at each
level.
The result of CacheDirLevels* CacheDirLength
must not be higher than 20.
CacheDirLevels Directive
| Description: | The number of levels of subdirectories in the cache. |
|---|---|
| Syntax: | CacheDirLevels levels |
| Default: | CacheDirLevels 2 |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_cache_disk |
The CacheDirLevels directive sets the number
of subdirectory levels in the cache. Cached data will be saved this
many directory levels below the CacheRoot directory.
A high value for CacheDirLevels combined
with a low value for CacheDirLength will result in
a relatively deep hierarchy, with a small number of subdirectories at each
level.
The result of CacheDirLevels*
CacheDirLength must
not be higher than 20.
CacheMaxFileSize Directive
| Description: | The maximum size (in bytes) of a document to be placed in the cache |
|---|---|
| Syntax: | CacheMaxFileSize bytes |
| Default: | CacheMaxFileSize 1000000 |
| Context: | server config, virtual host, directory, .htaccess |
| Status: | Extension |
| Module: | mod_cache_disk |
The CacheMaxFileSize directive sets the
maximum size, in bytes, for a document to be considered for storage in
the cache.
CacheMaxFileSize 64000
CacheMinFileSize Directive
| Description: | The minimum size (in bytes) of a document to be placed in the cache |
|---|---|
| Syntax: | CacheMinFileSize bytes |
| Default: | CacheMinFileSize 1 |
| Context: | server config, virtual host, directory, .htaccess |
| Status: | Extension |
| Module: | mod_cache_disk |
The CacheMinFileSize directive sets the
minimum size, in bytes, for a document to be considered for storage
in the cache.
CacheMinFileSize 64
CacheReadSize Directive
| Description: | The minimum size (in bytes) of the document to read and be cached before sending the data downstream |
|---|---|
| Syntax: | CacheReadSize bytes |
| Default: | CacheReadSize 0 |
| Context: | server config, virtual host, directory, .htaccess |
| Status: | Extension |
| Module: | mod_cache_disk |
The CacheReadSize directive sets the
minimum amount of data, in bytes, to be read from the backend before the
data is sent to the client. The default of zero causes all data read of
any size to be passed downstream to the client immediately as it arrives.
Setting this to a higher value causes the disk cache to buffer at least
this amount before sending the result to the client. This can improve
performance when caching content from a reverse proxy.
This directive only takes effect when the data is being saved to the cache, as opposed to data being served from the cache.
CacheReadSize 102400
CacheReadTime Directive
| Description: | The minimum time (in milliseconds) that should elapse while reading before data is sent downstream |
|---|---|
| Syntax: | CacheReadTime milliseconds |
| Default: | CacheReadTime 0 |
| Context: | server config, virtual host, directory, .htaccess |
| Status: | Extension |
| Module: | mod_cache_disk |
The CacheReadTime directive sets the minimum amount
of elapsed time that should pass before making an attempt to send data
downstream to the client. During the time period, data will be buffered
before sending the result to the client. This can improve performance when
caching content from a reverse proxy.
The default of zero disables this option.
This directive only takes effect when the data is being saved to the
cache, as opposed to data being served from the cache. It is recommended
that this option be used alongside the
CacheReadSize directive to
ensure that the server does not buffer excessively should data arrive faster
than expected.
CacheReadTime 1000
CacheRoot Directive
| Description: | The directory root under which cache files are stored |
|---|---|
| Syntax: | CacheRoot directory |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_cache_disk |
The CacheRoot directive defines the name of
the directory on the disk to contain cache files. If the mod_cache_disk module has been loaded or compiled in to the
Apache server, this directive must be defined. Failing to
provide a value for CacheRoot will result in
a configuration file processing error. The CacheDirLevels and CacheDirLength directives define
the structure of the directories under the specified root directory.
CacheRoot c:/cacheroot