Caching in drupal 7

Submitted by elyzium on Fri, 2019-03-22 17:40

Modules often have to make expensive database queries or calls to remote web services. Rather than
using resources for those operations every time they occur, modules can store a cache of their data into
one of the bins reserved for caching within the Drupal database, where bins are tables in the database.
Standard bins include the following:

cache: This is the generic cache storage bin. This bin is used to store variables ,the theme registry, locale date, a list of simple test, etc.
cache_block: This bin stores the content for various blocks.
cache_bootstrap: This bin stores information used during bootstrap.
cache_field: This bin stores loaded fields for an entity object.
cache_filter: This bin stores filtered pieces of content.
cache_form: This bin stores multistep forms.
cache_image: This bin stores information about in-progress image manipulations.
cache_menu: This bin stores the structure of visible navigation menus per page.
cache_page: This bin stores generated pages for anonymous users. This table is flushed often, whenever a page changes,
at least for every node and comment submission. This is the only bin affected by the page cache settings on the
administrator panel.
cache_path: This bin stores the system paths that have an alias.
cache_update: This bin stores available releases.

In general:
cache stores a copy of the variables table and the database schema and theme registry;
cache_block stores cached copies of blocks;
cache_bootstrap stores information that is used during the bootstrap process;
cache_field stores information about fields;
cache_image stores information about images;
cache_menu stores cached copies of the navigational menus;
cache_filter stores cached copies of each node’s content after it has been parsed by the filter system;
cache_form is used by the form API to avoid form building when possible;
cache_page stores cached copies of pages for anonymous users;
cache_path stores cached URL aliases;
cache_update stores information related to the current version of Drupal and modules used on your site.

It should be noted that the “Page cache” and “Block cache” settings at Configuration -> Performance affect only the
page cache and block cache tables, not the other cache components within Drupal. In other words,
filters, menus, and module settings are always cached.

Let’s take a look at the database structure of the cache table:

mysql> desc cache;
+------------+--------------+------+-----+---------+-------+
| Field      | Type         | Null | Key | Default | Extra |
+------------+--------------+------+-----+---------+-------+
| cid        | varchar(255) | NO   | PRI |         |       |
| data       | longblob     | YES  |     | NULL    |       |
| expire     | int(11)      | NO   | MUL | 0       |       |
| created    | int(11)      | NO   |     | 0       |       |
| serialized | smallint(6)  | NO   |     | 0       |       |
+------------+--------------+------+-----+---------+-------+

Module developers looking to take advantage of the cache API have two functions they need to know:
cache_set() and cache_get().

Using the Cache API
1. cache_set() is used for writing data to the cache. The function signature follows:
cache_set($cid, $data, $bin = 'cache', $expire = CACHE_PERMANENT)
And the function parameters are as follows:

• $cid: A unique cache ID string that acts as a key to the data. Colons are used to
delimit the hierarchy of possibilities.
• $bin: The name of the cache bin to store the data in. Valid core values are
'cache_block', 'cache_bootstrap', 'cache_field', 'cache_filter', 'cache_form',
'cache_menu', 'cache_page', 'cache_update', or 'cache' for the default cache.
• $data: The data to store in the cache. PHP objects and arrays will be automatically
serialized.
• $expire: The length of time for which the cached data is valid. Possible values are
CACHE_PERMANENT, CACHE_TEMPORARY, or a Unix timestamp. If a Unix timestamp is
given, the data will be treated as if it were marked CACHE_TEMPORARY after the
current time exceeds the Unix timestamp.

A common iteration pattern for cache_set() can be seen in modules/filter/filter.module:

// Store in cache with a minimum expiration time of 1 day.
if ($cache) {
cache_set($cid, $text, 'cache_filter', REQUEST_TIME + (60 * 60 * 24));
}

2.cache_get() is for retrieving the cached data. The function signature follows:
cache_get($cid, $bin = 'cache')
And the function parameters are as follows:

• $cid: This is the cache ID of the data to retrieve.
• $bin: This is the name of the cache bin to store the data in. Valid core values are
'cache_block', 'cache_bootstrap', 'cache_field', 'cache_filter', 'cache_form',
'cache_menu', 'cache_page', 'cache_update', or 'cache' for the default cache.

A common pattern for cache_get() can be seen in modules/filter/filter.module.

// Check for a cached version of this piece of text.
if ($cached = cache_get($cid, 'cache_filter')) {
return $cached->data;
}

Comments

Rickyapalk (not verified)

Tue, 2019-12-03 14:47

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