Subversion-Projekte lars-tiefland.prado

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<h1>Cache Models</h1>

<p>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 <tt>&lt;cacheModel&gt;</tt> element.

</p>

<p>The results from a query Mapped Statement can be cached simply by specifying

the <tt>cacheModel</tt> 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 <tt>cacheModel</tt> element as

follows:</p>

<com:TTextHighlighter Language="xml" CssClass="source">

<cacheModel id="product-cache" implementation="LRU" >

  <flushOnExecute  statement="insertProduct"/>

  <flushOnExecute  statement="updateProduct"/>

  <flushOnExecute  statement="deleteProduct"/>

  <property name="CacheSize" value="100"/>

</cacheModel>

</com:TTextHighlighter>

<p>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 <tt>type</tt> attribute is either a class name, or an alias for one

of the included implementations (see below). The cache will be flushed

whenever the <tt>insertProduct</tt>, <tt>updateProduct</tt>, or <tt>deleteProduct</tt>

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:</p>

<com:TTextHighlighter Language="xml" CssClass="source">

<statement id="getProductList" cacheModel="product-cache">

  select * from PRODUCT where PRD_CAT_ID = #value#

</statement>

</com:TTextHighlighter>

<h1>Cache Implementation</h1>

<p>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 <tt>cacheModel</tt> element as discussed above. The class name specified

must be an implementation of the <tt>ISqlMapCache</tt> 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

<tt>cacheModel</tt>. Currently there are 2 implementations included with the SQLMap PHP DataMapper.</p>

<div class="info"><b class="tip">Info:</b>

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.

</div>

<h2>Least Recently Used [LRU] Cache</h2>

<p>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.).</p>

<p>The LRU implementation is configured as follows:</p>

<com:TTextHighlighter Language="xml" CssClass="source">

<cacheModel id="product-cache"  implementation="LRU" >

  <flushOnExecute  statement="insertProduct"/>

  <flushOnExecute  statement="updateProduct"/>

  <flushOnExecute  statement="deleteProduct"/>

   <property name="CacheSize" value="100"/>

</cacheModel>

</com:TTextHighlighter>

<p>Only a single property is recognized by the LRU cache implementation. This

property, named <tt>CacheSize</tt> 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.</p>

<h2>FIFO Cache</h2>

<p>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.</p>

<p>The FIFO implementation is configured as follows:</p>

<com:TTextHighlighter Language="xml" CssClass="source">

<cacheModel id="product-cache" implementation="FIFO" >

  <flushOnExecute  statement="insertProduct"/>

  <flushOnExecute  statement="updateProduct"/>

  <flushOnExecute  statement="deleteProduct"/>

  <property name="CacheSize" value="100"/>

</cacheModel>

</com:TTextHighlighter>

<p>Only a single property is recognized by the FIFO cache implementation. This

property, named <tt>CacheSize</tt> 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.</p>

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