Cache Models

Some values in a database are know to change slower than others. To improve performance, many developers like to cache often-used data to avoid making unnecessary trips back to the database. SQLMap provides its own caching system, that you configure through a <cacheModel> element.

The results from a query Mapped Statement can be cached simply by specifying the cacheModel parameter in the statement tag (seen above). A cache model is a configured cache that is defined within your DataMapper configuration file. Cache models are configured using the cacheModel element as follows:

The cache model above will create an instance of a cache named "product-cache" that uses a Least Recently Used (LRU) implementation. The value of the type attribute is either a class name, or an alias for one of the included implementations (see below). The cache will be flushed whenever the insertProduct, updateProduct, or deleteProduct mapped statements are executed. There can be any number of "flush on execute" elements specified for a cache. Some cache implementations may need additional properties, such as the "cache-size" property demonstrated above. In the case of the LRU cache, the size determines the number of entries to store in the cache. Once a cache model is configured, you can specify the cache model to be used by a mapped statement, for example:

select * from PRODUCT where PRD_CAT_ID = #value#

Cache Implementation

The cache model uses a pluggable framework for supporting different types of caches. The choice of cache is specified in the "implementation" attribute of the cacheModel element as discussed above. The class name specified must be an implementation of the ISqlMapCache interface, or one of the two aliases discussed below. Further configuration parameters can be passed to the implementation via the property elements contained within the body of the cacheModel. Currently there are 2 implementations included with the SQLMap PHP DataMapper.

Info: The cache implementations, LRU and FIFO cache below do not persist across requests. That is, once the request is complete, all cache data is lost. These caches are useful queries that results in the same repeated data during the current request.

Least Recently Used [LRU] Cache

The LRU cache implementation uses an Least Recently Used algorithm to determines how objects are automatically removed from the cache. When the cache becomes over full, the object that was accessed least recently will be removed from the cache. This way, if there is a particular object that is often referred to, it will stay in the cache with the least chance of being removed. The LRU cache makes a good choice for applications that have patterns of usage where certain objects may be popular to one or more users over a longer period of time (e.g. navigating back and forth between paginated lists, popular search keys etc.).

The LRU implementation is configured as follows:

Only a single property is recognized by the LRU cache implementation. This property, named CacheSize must be set to an integer value representing the maximum number of objects to hold in the cache at once. An important thing to remember here is that an object can be anything from a single string instance to an array of object. So take care not to store too much in your cache and risk running out of memory.

FIFO Cache

The FIFO cache implementation uses an First In First Out algorithm to determines how objects are automatically removed from the cache. When the cache becomes over full, the oldest object will be removed from the cache. The FIFO cache is good for usage patterns where a particular query will be referenced a few times in quick succession, but then possibly not for some time later.

The FIFO implementation is configured as follows:

Only a single property is recognized by the FIFO cache implementation. This property, named CacheSize must be set to an integer value representing the maximum number of objects to hold in the cache at once. An important thing to remember here is that an object can be anything from a single String instance to an array of object. So take care not to store too much in your cache and risk running out of memory.