From 33c36f2a13af36753779ca4bc6ebf2ef65582fd8 Mon Sep 17 00:00:00 2001 From: resurtm Date: Wed, 3 Jul 2013 16:26:06 +0600 Subject: [PATCH] Docs: caching WIP. --- docs/guide/caching.md | 190 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 190 insertions(+) diff --git a/docs/guide/caching.md b/docs/guide/caching.md index cd945e7..f5c7a2e 100644 --- a/docs/guide/caching.md +++ b/docs/guide/caching.md @@ -1,3 +1,193 @@ Caching ======= +Overview and Base Concepts +-------------------------- + +Caching is a cheap and effective way to improve the performance of a web application. By storing relatively +static data in cache and serving it from cache when requested, we save the time needed to generate the data. + +Using cache in Yii mainly involves configuring and accessing a cache application component. The following +application configuration specifies a cache component that uses [memcached](http://memcached.org/) with +two cache servers. + +```php +'components' => array( + 'cache' => array( + 'class' => '\yii\caching\MemCache', + 'servers' => array( + array( + 'host' => 'server1', + 'port' => 11211, + 'weight' => 100, + ), + array( + 'host' => 'server2', + 'port' => 11211, + 'weight' => 50, + ), + ), + ), +), +``` + +When the application is running, the cache component can be accessed through `Yii::$app->cache` call. + +Yii provides various cache components that can store cached data in different media. For example, +the [[\yii\caching\MemCache]] component encapsulates the PHP [memcache](http://php.net/manual/en/book.memcache.php) +and [memcached](http://php.net/manual/en/book.memcached.php) extensions and uses memory as the medium +of cache storage; the [[\yii\caching\ApcCache]] component encapsulates the PHP +[APC](http://php.net/manual/en/book.apc.php) extension; and the [[\yii\caching\DbCache]] component stores +cached data in database table. + +The following is a summary of the available cache components: + +* [[\yii\caching\ApcCache]]: uses PHP [APC](http://php.net/manual/en/book.apc.php) extension. This option can be + considered as the fastest one when dealing with cache for a centralized thick application (e.g. one + server, no dedicated load balancers, etc.). + +* [[\yii\caching\DbCache]]: uses a database table to store cached data. By default, it will create and use a + [SQLite3](http://sqlite.org/) database under the runtime directory. You can explicitly specify a database for + it to use by setting its `db` property. + +* [[\yii\caching\DummyCache]]: presents dummy cache that does no caching at all. The purpose of this component + is to simplify the code that needs to check the availability of cache. For example, during development or if + the server doesn't have actual cache support, we can use this cache component. When an actual cache support + is enabled, we can switch to use the corresponding cache component. In both cases, we can use the same + code `Yii::$app->cache->get($key)` to attempt retrieving a piece of data without worrying that + `Yii::$all->cache` might be `null`. + +* [[\yii\caching\FileCache]]: uses standard files to store cached data. This is particular suitable + to cache large chunk of data (such as pages). + +* [[\yii\caching\MemCache]]: uses PHP [memcache](http://php.net/manual/en/book.memcache.php) + and [memcached](http://php.net/manual/en/book.memcached.php) extensions. This option can be considered as + the fastest one when dealing with cache in a distributed applications (e.g. with several servers, load + balancers, etc.) + +* [[\yii\caching\RedisCache]]: implements a cache component based on [Redis](http://redis.io/) NoSQL database. + +* [[\yii\caching\WinCache]]: uses PHP [WinCache](http://iis.net/downloads/microsoft/wincache-extension) + ([see also](http://php.net/manual/en/book.wincache.php)) extension. + +* [[\yii\caching\XCache]]: uses PHP [XCache](http://xcache.lighttpd.net/) extension. + +* [[\yii\caching\ZendDataCache]]: uses + [Zend Data Cache](http://files.zend.com/help/Zend-Server-6/zend-server.htm#data_cache_component.htm) + as the underlying caching medium. + +Tip: because all these cache components extend from the same base class [[Cache]], one can switch to use +a different type of cache without modifying the code that uses cache. + +Caching can be used at different levels. At the lowest level, we use cache to store a single piece of data, +such as a variable, and we call this data caching. At the next level, we store in cache a page fragment which +is generated by a portion of a view script. And at the highest level, we store a whole page in cache and serve +it from cache as needed. + +In the next few subsections, we elaborate how to use cache at these levels. + +Note, by definition, cache is a volatile storage medium. It does not ensure the existence of the cached +data even if it does not expire. Therefore, do not use cache as a persistent storage (e.g. do not use cache +to store session data or other valuable information). + +Data Caching +------------ + +Data caching is about storing some PHP variable in cache and retrieving it later from cache. For this purpose, +the cache component base class [[\yii\caching\Cache]] provides two methods that are used most of the time: +[[set()]] and [[get()]]. Note, only serializable variables and objects could be cached successfully. + +To store a variable `$value` in cache, we choose a unique `$key` and call [[set()]] to store it: + +```php +Yii::$app->cache->set($key, $value); +``` + +The cached data will remain in the cache forever unless it is removed because of some caching policy +(e.g. caching space is full and the oldest data are removed). To change this behavior, we can also supply +an expiration parameter when calling [[set()]] so that the data will be removed from the cache after +a certain period of time: + +```php +// keep the value in cache for at most 45 seconds +Yii::$app->cache->set($key, $value, 45); +``` + +Later when we need to access this variable (in either the same or a different web request), we call [[get()]] +with the key to retrieve it from cache. If the value returned is `false`, it means the value is not available +in cache and we should regenerate it: + +```php +public function getCachedData() +{ + $key = /* generate unique key here */; + $value = Yii::$app->getCache()->get($key); + if ($value === false) { + $value = /* regenerate value because it is not found in cache and then save it in cache for later use */; + Yii::$app->cache->set($id, $value); + } + return $value; +} +``` + +This is the common pattern of arbitrary data caching for general use. + +When choosing the key for a variable to be cached, make sure the key is unique among all other variables that +may be cached in the application. It is **NOT** required that the key is unique across applications because +the cache component is intelligent enough to differentiate keys for different applications. + +Some cache storages, such as MemCache, APC, support retrieving multiple cached values in a batch mode, +which may reduce the overhead involved in retrieving cached data. A method named [[mget()]] is provided +to exploit this feature. In case the underlying cache storage does not support this feature, +[[mget()]] will still simulate it. + +To remove a cached value from cache, call [[delete()]]; and to remove everything from cache, call [[flush()]]. +Be very careful when calling [[flush()]] because it also removes cached data that are from other applications. + +Note, because CCache implements ArrayAccess, a cache component can be used liked an array. The followings +are some examples: + +```php +$cache = Yii::$app->getComponent('cache'); +$cache['var1'] = $value1; // equivalent to: $cache->set('var1', $value1); +$value2 = $cache['var2']; // equivalent to: $value2 = $cache->get('var2'); +``` + +### Cache Dependency + +TBD: http://www.yiiframework.com/doc/guide/1.1/en/caching.data#cache-dependency + +### Query Caching + +TBD: http://www.yiiframework.com/doc/guide/1.1/en/caching.data#query-caching + +Fragment Caching +---------------- + +TBD: http://www.yiiframework.com/doc/guide/1.1/en/caching.fragment + +### Caching Options + +TBD: http://www.yiiframework.com/doc/guide/1.1/en/caching.fragment#caching-options + +### Nested Caching + +TBD: http://www.yiiframework.com/doc/guide/1.1/en/caching.fragment#nested-caching + +Dynamic Content +--------------- + +TBD: http://www.yiiframework.com/doc/guide/1.1/en/caching.dynamic + +Page Caching +------------ + +TBD: http://www.yiiframework.com/doc/guide/1.1/en/caching.page + +### Output Caching + +TBD: http://www.yiiframework.com/doc/guide/1.1/en/caching.page#output-caching + +### HTTP Caching + +TBD: http://www.yiiframework.com/doc/guide/1.1/en/caching.page#http-caching