# Zend_Cache Backends

There are two kinds of backends: standard ones and extended ones. Of course, extended backends offer more features.

## Zend_Cache_Backend_File

This (extended) backends stores cache records into files (in a chosen directory).

Available options are :

File Backend Options

Option | Data Type | Default Value | Description
--- | --- | --- | ---
cache_dir | String | [system temp dir] | Directory where to store cache files
file_locking | Boolean | `TRUE` | Enable or disable file_locking : Can avoid cache corruption under bad circumstances but it doesn't help on multithread webservers or on NFS filesystems...
read_control | Boolean | `TRUE` | Enable / disable read control : if enabled, a control key is embedded in the cache file and this key is compared with the one calculated after the reading.
read_control_type | String | 'crc32' | Type of read control (only if read control is enabled). Available values are : 'md5' (best but slowest), 'crc32' (lightly less safe but faster, better choice), 'adler32' (new choice, faster than crc32), 'strlen' for a length only test (fastest).
hashed_directory_level | Integer | 0 | Hashed directory structure level : 0 means "no hashed directory structure", 1 means "one level of directory", 2 means "two levels"... This option can speed up the cache only when you have many thousands of cache files. Only specific benchs can help you to choose the perfect value for you. Maybe, 1 or 2 is a good start.
hashed_directory_perm | Integer | 0700 | Permissins for the hashed directory structure
file_name_prefix | String | 'zend_cache' | prefix for cache files ; be really careful with this option because a too generic value in a system cache dir (like `/tmp`) can cause disasters when cleaning the cache
cache_file_umask | Integer | 0600 | umask for cache files
cache_file_perm | Integer | 0600 | Permissions for cache files
metatadatas_array_max_size | Integer | 100 | internal max size for the metadatas array (don't change this value unless you know what you are doing)

## Zend_Cache_Backend_Sqlite

This (extended) backends stores cache records into a SQLite database.

Available options are :

Sqlite Backend Options

Option | Data Type | Default Value | Description
--- | --- | --- | ---
cache_db_complete_path (mandatory) | String | `NULL` | The complete path (filename included) of the SQLite database
automatic_vacuum_factor | Integer | 10 | Disable / Tune the automatic vacuum process. The automatic vacuum process defragment the database file (and make it smaller) when a clean() or delete() is called: 0 means no automatic vacuum ; 1 means systematic vacuum (when delete() or clean() methods are called) ; x (integer) > 1 => automatic vacuum randomly 1 times on x clean() or delete().

## Zend_Cache_Backend_Memcached

This (extended) backends stores cache records into a memcached server. memcached is a high-performance, distributed memory object caching system. To use this backend, you need a memcached daemon and the memcache PECL extension.

Be careful : with this backend, "tags" are not supported for the moment as the "doNotTestCacheValidity=true" argument.

Available options are :

Memcached Backend Options

Option | Data Type | Default Value | Description
--- | --- | --- | ---
servers | Array | `array(array('host' => 'localhost', 'port' => 11211, 'persistent' => true, 'weight' => 1, 'timeout' => 5, 'retry_interval' => 15, 'status' => true, 'failure_callback' => '' ))` | An array of memcached servers ; each memcached server is described by an associative array : 'host' => (string) : the name of the memcached server, 'port' => (int) : the port of the memcached server, 'persistent' => (bool) : use or not persistent connections to this memcached server 'weight' => (int) :the weight of the memcached server, 'timeout' => (int) :the time out of the memcached server, 'retry_interval' => (int) :the retry interval of the memcached server, 'status' => (bool) :the status of the memcached server, 'failure_callback' => (callback) : the failure_callback of the memcached server
compression | Boolean | `FALSE` | `TRUE` if you want to use on-the-fly compression
compatibility | Boolean | `FALSE` | `TRUE` if you want to use this compatibility mode with old memcache servers or extensions

## Zend_Cache_Backend_Libmemcached

This (extended) backend stores cache records into a memcached server. memcached is a high-performance, distributed memory object caching system. To use this backend, you need a memcached daemon and the memcached PECL extension.

Be careful : with this backend, "tags" are not supported for the moment as the "doNotTestCacheValidity=true" argument.

Available options are :

Libmemcached Backend Options

Option | Data Type | Default Value | Description
--- | --- | --- | ---
servers | Array | `array(array('host' => 'localhost', 'port' => 11211, 'weight' => 1))` | An array of memcached servers ; each memcached server is described by an associative array: 'host' => (string) : the name of the memcached server, 'port' => (int) : the port of the memcached server, 'weight' => (int) :the weight of the memcached server
client | Array | `array( Memcached::OPT_DISTRIBUTION => Memcached::DISTRIBUTION_CONSISTENT, Memcached::OPT_HASH => Memcached::HASH_MD5, Memcached::OPT_LIBKETAMA_COMPATIBLE => true )` | An associative array of memcached client options ; The array key can be the name of the memcached option constant (without 'OPT_') or the integer value of it. See Memcached constants on PHP manual

## Zend_Cache_Backend_Apc

This (extended) backends stores cache records in shared memory through the APC (Alternative PHP Cache) extension (which is of course need for using this backend).

Be careful : with this backend, "tags" are not supported for the moment as the "doNotTestCacheValidity=true" argument.

There is no option for this backend.

## Zend_Cache_Backend_Xcache

This backends stores cache records in shared memory through the XCache extension (which is of course need for using this backend).

Be careful : with this backend, "tags" are not supported for the moment as the "doNotTestCacheValidity=true" argument.

Available options are :

Xcache Backend Options

Option | Data Type | Default Value | Description
--- | --- | --- | ---
user | String | `NULL` | `xcache.admin.user`, necessary for the clean() method
password | String | `NULL` | `xcache.admin.pass` (in clear form, not MD5), necessary for the clean() method

## Zend_Cache_Backend_ZendPlatform

This backend uses content caching API of the Zend Platform product. Naturally, to use this backend you need to have Zend Platform installed.

This backend supports tags, but does not support `CLEANING_MODE_NOT_MATCHING_TAG` cleaning mode.

Specify this backend using a word separator -- '-', '.', ' ', or '_' -- between the words 'Zend' and 'Platform' when using the Zend_Cache::factory() method:

    $cache = Zend_Cache::factory('Core', 'Zend Platform');

There are no options for this backend.

## Zend_Cache_Backend_TwoLevels

This (extend) backend is an hybrid one. It stores cache records in two other backends : a fast one (but limited) like Apc, Memcache... and a "slow" one like File, Sqlite...

This backend will use the priority parameter (given at the frontend level when storing a record) and the remaining space in the fast backend to optimize the usage of these two backends.

Specify this backend using a word separator -- '-', '.', ' ', or '_' -- between the words 'Two' and 'Levels' when using the Zend_Cache::factory() method:

    $cache = Zend_Cache::factory('Core', 'Two Levels');

Available options are :

TwoLevels Backend Options

Option | Data Type | Default Value | Description
--- | --- | --- | ---
slow_backend | String | File | the "slow" backend name
fast_backend | String | Apc | the "fast" backend name
slow_backend_options | Array | array() | the "slow" backend options
fast_backend_options | Array | array() | the "fast" backend options
slow_backend_custom_naming | Boolean | `FALSE` | if `TRUE`, the slow_backend argument is used as a complete class name; if `FALSE`, the frontend argument is used as the end of "Zend_Cache_Backend_[...]" class name
fast_backend_custom_naming | Boolean | `FALSE` | if `TRUE`, the fast_backend argument is used as a complete class name; if `FALSE`, the frontend argument is used as the end of "Zend_Cache_Backend_[...]" class name
slow_backend_autoload | Boolean | `FALSE` | if `TRUE`, there will no require_once for the slow backend (useful only for custom backends)
fast_backend_autoload | Boolean | `FALSE` | if `TRUE`, there will no require_once for the fast backend (useful only for custom backends)
auto_refresh_fast_cache | Boolean | `TRUE` | if `TRUE`, auto refresh the fast cache when a cache record is hit
stats_update_factor | Integer | 10 | disable / tune the computation of the fast backend filling percentage (when saving a record into cache, computation of the fast backend filling percentage randomly 1 times on x cache writes)

## Zend_Cache_Backend_ZendServer_Disk and Zend_Cache_Backend_ZendServer_ShMem

These backends store cache records using Zend Server caching functionality.

Be careful: with these backends, "tags" are not supported for the moment as the "doNotTestCacheValidity=true" argument.

These backend work only withing Zend Server environment for pages requested through HTTP or HTTPS and don't work for command line script execution

Specify this backend using parameter customBackendNaming as `TRUE` when using the Zend_Cache::factory() method:

    $cache = Zend_Cache::factory('Core', 'Zend_Cache_Backend_ZendServer_Disk',
                                 $frontendOptions, $backendOptions, false, true);

There is no option for this backend.

## Zend_Cache_Backend_Static

This backend works in concert with Zend_Cache_Frontend_Capture (the two must be used together) to save the output from requests as static files. This means the static files are served directly on subsequent requests without any involvement of PHP or Zend Framework at all.

Zend_Cache_Frontend_Capture operates by registering a callback function to be called when the output buffering it uses is cleaned. In order for this to operate correctly, it must be the final output buffer in the request. To guarantee this, the output buffering used by the Dispatcher must be disabled by calling Zend_Controller_Front's setParam() method, for example, `$front->setParam('disableOutputBuffering', true);` or adding "resources.frontcontroller.params.disableOutputBuffering = true" to your bootstrap configuration file (assumed INI) if using Zend_Application.

The benefits of this cache include a large throughput increase since all subsequent requests return the static file and don't need any dynamic processing. Of course this also has some disadvantages. The only way to retry the dynamic request is to purge the cached file from elsewhere in the application (or via a cronjob if timed). It is also restricted to single-server applications where only one filesystem is used. Nevertheless, it can be a powerful means of getting more performance without incurring the cost of a proxy on single machines.

Before describing its options, you should note this needs some changes to the default `.htaccess` file in order for requests to be directed to the static files if they exist. Here's an example of a simple application caching some content, including two specific feeds which need additional treatment to serve a correct Content-Type header:

    AddType application/rss+xml .xml
    AddType application/atom+xml .xml

    RewriteEngine On

    RewriteCond %{REQUEST_URI} feed/rss$
    RewriteCond %{DOCUMENT_ROOT}/cached/%{REQUEST_URI}.xml -f
    RewriteRule .* cached/%{REQUEST_URI}.xml [L,T=application/rss+xml]

    RewriteCond %{REQUEST_URI} feed/atom$
    RewriteCond %{DOCUMENT_ROOT}/cached/%{REQUEST_URI}.xml -f
    RewriteRule .* cached/%{REQUEST_URI}.xml [L,T=application/atom+xml]

    RewriteCond %{DOCUMENT_ROOT}/cached/index.html -f
    RewriteRule ^/*$ cached/index.html [L]
    RewriteCond %{DOCUMENT_ROOT}/cached/%{REQUEST_URI}.(html|xml|json|opml|svg) -f
    RewriteRule .* cached/%{REQUEST_URI}.%1 [L]

    RewriteCond %{REQUEST_FILENAME} -s [OR]
    RewriteCond %{REQUEST_FILENAME} -l [OR]
    RewriteCond %{REQUEST_FILENAME} -d
    RewriteRule ^.*$ - [NC,L]

    RewriteRule ^.*$ index.php [NC,L]

The above assumes static files are cached to the directory `./public/cached`. We'll cover the option setting this location, "public_dir", below.

Due to the nature of static file caching, the backend class offers two additional methods: remove() and removeRecursively(). Both accept a request URI, which when mapped to the "public_dir" where static files are cached, and has a pre-stored extension appended, provides the name of either a static file to delete, or a directory path to delete recursively. Due to the restraints of Zend_Cache_Backend_Interface, all other methods such as save() accept an ID which is calculated by applying bin2hex() to a request URI.

Given the level at which static caching operates, static file caching is addressed for simpler use with the Zend_Controller_Action_Helper_Cache action helper. This helper assists in setting which actions of a controller to cache, with what tags, and with which extension. It also offers methods for purging the cache by request URI or tag. Static file caching is also assisted by Zend_Cache_Manager which includes pre-configured configuration templates for a static cache (as `Zend_Cache_Manager::PAGECACHE` or "page"). The defaults therein can be configured as needed to set up a "public_dir" location for caching, etc.

It should be noted that the static cache actually uses a secondary cache to store tags (obviously we can't store them elsewhere since a static cache does not invoke PHP if working correctly). This is just a standard Core cache, and should use a persistent backend such as File or TwoLevels (to take advantage of memory storage without sacrificing permanent persistance). The backend includes the option "tag_cache" to set this up (it is obligatory), or the setInnerCache() method.

Static Backend Options

Option | Data Type | Default Value | Description
--- | --- | --- | ---
public_dir | String | `NULL` | Directory where to store static files. This must exist in your public directory.
file_locking | Boolean | `TRUE` | Enable or disable file_locking : Can avoid cache corruption under bad circumstances but it doesn't help on multithread webservers or on NFS filesystems...
read_control | Boolean | `TRUE` | Enable / disable read control : if enabled, a control key is embedded in the cache file and this key is compared with the one calculated after the reading.
read_control_type | String | 'crc32' | Type of read control (only if read control is enabled). Available values are : 'md5' (best but slowest), 'crc32' (lightly less safe but faster, better choice), 'adler32' (new choice, faster than crc32), 'strlen' for a length only test (fastest).
cache_file_umask | Integer | 0600 | umask for cached files.
cache_directory_umask | Integer | 0700 | Umask for directories created within public_dir.
file_extension | String | '`.html`' | Default file extension for static files created. This can be configured on the fly, see Zend_Cache_Backend_Static::save() though generally it's recommended to rely on Zend_Controller_Action_Helper_Cache when doing so since it's simpler that way than messing with arrays or serialization manually.
index_filename | String | 'index' | If a request URI does not contain sufficient information to construct a static file (usually this means an index call, e.g. URI of '/'), the index_filename is used instead. So '' or '/' would map to '`index.html`' (assuming the default file_extension is '`.html`').
tag_cache | Object | `NULL` | Used to set an 'inner' cache utilised to store tags and file extensions associated with static files. This must be set or the static cache cannot be tracked and managed.
disable_caching | Boolean | `FALSE` | If set to `TRUE`, static files will not be cached. This will force all requests to be dynamic even if marked to be cached in Controllers. Useful for debugging.