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51Database Caching Class
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65<h1>Database Caching Class</h1>
66
admin5294f4f2006-10-06 02:10:05 +0000[diff] [blame^]67<p>The Database Caching Class permits you to cache your queries as text files for reduced database load.</p>
admin43a823e2006-09-27 01:57:10 +0000[diff] [blame]68
admin5ffba1e2006-10-05 04:23:18 +0000[diff] [blame]69<p class="important"><strong>Important:</strong>&nbsp; This class is initialized automatically by the database driver
admin5294f4f2006-10-06 02:10:05 +0000[diff] [blame^]70when caching is enabled. Do NOT load this class manually.<br /><br />
admin43a823e2006-09-27 01:57:10 +0000[diff] [blame]71
admin5294f4f2006-10-06 02:10:05 +0000[diff] [blame^]72<strong>Also note:</strong>&nbsp; Not all query result functions are available when you use caching. Please read this page carefully.</p>
admin43a823e2006-09-27 01:57:10 +0000[diff] [blame]73
admin11c06c72006-10-05 05:12:27 +0000[diff] [blame]74<h2>Enabling Caching</h2>
75
admin5294f4f2006-10-06 02:10:05 +0000[diff] [blame^]76<p>Caching is enabled in three steps:</p>
admin11c06c72006-10-05 05:12:27 +0000[diff] [blame]77
78<ul>
admin5294f4f2006-10-06 02:10:05 +0000[diff] [blame^]79<li>Create a writable directory on your server where the cache files can be stored.</li>
80<li>Set the path to your cache folder in your <dfn>application/config/database.php</dfn> file.</li>
81<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>
admin11c06c72006-10-05 05:12:27 +0000[diff] [blame]82</ul>
admin43a823e2006-09-27 01:57:10 +0000[diff] [blame]83
84
admin5294f4f2006-10-06 02:10:05 +0000[diff] [blame^]85<h2>How Does Caching Work?</h2>
adminf3428b52006-10-05 05:19:15 +0000[diff] [blame]86
admin5294f4f2006-10-06 02:10:05 +0000[diff] [blame^]87<p>Code Igniter's query caching system happens dynamically when your pages are viewed.
88When caching is enabled, the first time a webpage is loaded, the query result object will
89be 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
90accessing your database. Your database usage can effectively be reduced to zero for any pages that have been cached.</p>
adminf3428b52006-10-05 05:19:15 +0000[diff] [blame]91
admin5294f4f2006-10-06 02:10:05 +0000[diff] [blame^]92<p>Only <dfn>read-type</dfn> (SELECT) queries can be cached, since these are the only type of queries that produce a result.
93<dfn>Write-type</dfn> (INSERT, UPDATE, etc.) queries, since they don't generate a result, will not be cached by the system.</p>
adminf3428b52006-10-05 05:19:15 +0000[diff] [blame]94
admin5294f4f2006-10-06 02:10:05 +0000[diff] [blame^]95<p>Cache files do NOT expire. Any queries that have been cached will remain cached until you delete them. The caching system does
96have an "auto-delete"feature, as described below. It also lets you manually clear caches associated with individulal pages, or
97you can delete the entire collection of cache files.</p>
adminf3428b52006-10-05 05:19:15 +0000[diff] [blame]98
admin5294f4f2006-10-06 02:10:05 +0000[diff] [blame^]99<h2>Will Caching Improve Your Site's Performance?</h2>
100
101<p>Maybe. Whether you see a performance gain as a result of caching depends on many factors.
102For example, if you have a highly optimized database under very little load, you probably won't see a performance boost.
103If your database is under heavy use you probably will see an improved response, assuming your filesystem is not
104overly taxed. Remember that caching simply changes how your information is retrieved, shifting it from being a database
105operation to a filesystem one.</p>
106
107<p>In some clustered server environments caching may be detrimental since filesystem operations are so intense.
108On single servers (particularly in shared enironments) caching will probably be beneficial. Unfortunately there is no
109single answer to the question of whether you should cache your database. It really depends on your situation.</p>
110
111<h2>How are Cache Files Stored?</h2>
112
113<p>Code Igniter places the result of EACH query into its own cache file. Sets of cache files are further organized into
114sub-folders corrsponding to your controller functions.</p>
115
116<p>For example, let's say you have a controller called <dfn>blog</dfn> with a function called <dfn>comments</dfn> that
117contains three queries. The caching system will create a cache folder
118called <kbd>blog_comments</kbd>, into which it will write three cache files.</p>
119
120<p>If your have dynamic queries that change based on inormation in your URI (when using pagination, for example), each instance of
121the query will produce its own cache file. It's possible, therefore, to end up with many times more cache files than you have
122queries.</p>
adminf3428b52006-10-05 05:19:15 +0000[diff] [blame]123
124
admin5294f4f2006-10-06 02:10:05 +0000[diff] [blame^]125<h2>Managing your Cache Files</h2>
126
127<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
128that allows user commenting. Whenever a new comment is submitted you'll want to delete the cache files associated with the
129controller function that serves up your comments. You'll find two delete functions described below that help you
130clear data.</p>
adminf3428b52006-10-05 05:19:15 +0000[diff] [blame]131
132
admin5294f4f2006-10-06 02:10:05 +0000[diff] [blame^]133<h1>Function Reference</h1>
adminf3428b52006-10-05 05:19:15 +0000[diff] [blame]134
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