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authorKyle Farris <kylefarris@kylefarris.gotdns.org>2011-10-14 21:43:25 +0200
committerKyle Farris <kylefarris@kylefarris.gotdns.org>2011-10-14 21:43:25 +0200
commitad17f4b932b3728c1e299b48f28b3ae0dbdd6b0b (patch)
treefdb357433e76000bdef60c4d18e5ab0540b07aeb /user_guide/database/caching.html
parentdb46d02ac23b8e0bc2416e197494d3b795b57530 (diff)
parenta2125a5d830fd390b4cf35f77e9bb0558cfa2dd7 (diff)
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-<h1>Database Caching Class</h1>
-
-<p>The Database Caching Class permits you to cache your queries as text files for reduced database load.</p>
-
-<p class="important"><strong>Important:</strong>&nbsp; This class is initialized automatically by the database driver
-when caching is enabled. Do NOT load this class manually.<br /><br />
-
-<strong>Also note:</strong>&nbsp; Not all query result functions are available when you use caching. Please read this page carefully.</p>
-
-<h2>Enabling Caching</h2>
-
-<p>Caching is enabled in three steps:</p>
-
-<ul>
-<li>Create a writable directory on your server where the cache files can be stored.</li>
-<li>Set the path to your cache folder in your <dfn>application/config/database.php</dfn> file.</li>
-<li>Enable the caching feature, either globally by setting the preference in your <dfn>application/config/database.php</dfn> file, or manually as described below.</li>
-</ul>
-
-<p>Once enabled, caching will happen automatically whenever a page is loaded that contains database queries.</p>
-
-
-<h2>How Does Caching Work?</h2>
-
-<p>CodeIgniter's query caching system happens dynamically when your pages are viewed.
-When caching is enabled, the first time a web page is loaded, the query result object will
-be serialized and stored in a text file on your server. The next time the page is loaded the cache file will be used instead of
-accessing your database. Your database usage can effectively be reduced to zero for any pages that have been cached.</p>
-
-<p>Only <dfn>read-type</dfn> (SELECT) queries can be cached, since these are the only type of queries that produce a result.
-<dfn>Write-type</dfn> (INSERT, UPDATE, etc.) queries, since they don't generate a result, will not be cached by the system.</p>
-
-<p>Cache files DO NOT expire. Any queries that have been cached will remain cached until you delete them. The caching system
-permits you clear caches associated with individual pages, or you can delete the entire collection of cache files.
-Typically you'll want to use the housekeeping functions described below to delete cache files after certain
-events take place, like when you've added new information to your database.</p>
-
-<h2>Will Caching Improve Your Site's Performance?</h2>
-
-<p>Getting a performance gain as a result of caching depends on many factors.
-If you have a highly optimized database under very little load, you probably won't see a performance boost.
-If your database is under heavy use you probably will see an improved response, assuming your file-system is not
-overly taxed. Remember that caching simply changes how your information is retrieved, shifting it from being a database
-operation to a file-system one.</p>
-
-<p>In some clustered server environments, for example, caching may be detrimental since file-system operations are so intense.
-On single servers in shared environments, caching will probably be beneficial. Unfortunately there is no
-single answer to the question of whether you should cache your database. It really depends on your situation.</p>
-
-<h2>How are Cache Files Stored?</h2>
-
-<p>CodeIgniter places the result of EACH query into its own cache file. Sets of cache files are further organized into
-sub-folders corresponding to your controller functions. To be precise, the sub-folders are named identically to the
-first two segments of your URI (the controller class name and function name).</p>
-
-<p>For example, let's say you have a controller called <dfn>blog</dfn> with a function called <dfn>comments</dfn> that
-contains three queries. The caching system will create a cache folder
-called <kbd>blog+comments</kbd>, into which it will write three cache files.</p>
-
-<p>If you use dynamic queries that change based on information in your URI (when using pagination, for example), each instance of
-the query will produce its own cache file. It's possible, therefore, to end up with many times more cache files than you have
-queries.</p>
-
-
-<h2>Managing your Cache Files</h2>
-
-<p>Since cache files do not expire, you'll need to build deletion routines into your application. For example, let's say you have a blog
-that allows user commenting. Whenever a new comment is submitted you'll want to delete the cache files associated with the
-controller function that serves up your comments. You'll find two delete functions described below that help you
-clear data.</p>
-
-
-<h2>Not All Database Functions Work with Caching</h2>
-
-<p>Lastly, we need to point out that the result object that is cached is a simplified version of the full result object. For that reason,
-some of the query result functions are not available for use.</p>
-
-<p>The following functions <kbd>ARE NOT</kbd> available when using a cached result object:</p>
-
-<ul>
-<li>num_fields()</li>
-<li>field_names()</li>
-<li>field_data()</li>
-<li>free_result()</li>
-</ul>
-
-<p>Also, the two database resources (result_id and conn_id) are not available when caching, since result resources only
-pertain to run-time operations.</p>
-
-
-<br />
-
-<h1>Function Reference</h1>
-
-
-
-<h2>$this->db->cache_on()&nbsp; / &nbsp; $this->db->cache_off()</h2>
-
-<p>Manually enables/disables caching. This can be useful if you want to
-keep certain queries from being cached. Example:</p>
-
-<code>
-// Turn caching on<br />
-$this->db->cache_on();<br />
-$query = $this->db->query("SELECT * FROM mytable");<br />
-<br />
-// Turn caching off for this one query<br />
-$this->db->cache_off();<br />
-$query = $this->db->query("SELECT * FROM members WHERE member_id = '$current_user'");<br />
-<br />
-// Turn caching back on<br />
-$this->db->cache_on();<br />
-$query = $this->db->query("SELECT * FROM another_table");
-</code>
-
-
-<h2>$this->db->cache_delete()</h2>
-
-<p>Deletes the cache files associated with a particular page. This is useful if you need to clear caching after you update your database.</p>
-
-<p>The caching system saves your cache files to folders that correspond to the URI of the page you are viewing. For example, if you are viewing
-a page at <dfn>example.com/index.php/blog/comments</dfn>, the caching system will put all cache files associated with it in a folder
-called <dfn>blog+comments</dfn>. To delete those particular cache files you will use:</p>
-
-<code>$this->db->cache_delete('blog', 'comments');</code>
-
-<p>If you do not use any parameters the current URI will be used when determining what should be cleared.</p>
-
-
-<h2>$this->db->cache_delete_all()</h2>
-
-<p>Clears all existing cache files. Example:</p>
-
-<code>$this->db->cache_delete_all();</code>
-
-
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