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51Database Caching Class
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65<h1>Database Caching Class</h1>
66
67<p>The Database Caching Class contains functions that permit you to cache your queries.</p>
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
admin11c06c72006-10-05 05:12:27 +0000[diff] [blame]70when caching is enabled. Do NOT load this class manually.
admin43a823e2006-09-27 01:57:10 +0000[diff] [blame]71More info below...</p>
72
admin5ffba1e2006-10-05 04:23:18 +0000[diff] [blame]73<h2>How Does Caching Work?</h2>
admin43a823e2006-09-27 01:57:10 +0000[diff] [blame]74
admin11c06c72006-10-05 05:12:27 +0000[diff] [blame]75<p>When caching is enabled, anytime a "read" type query (SELECT) is run, the result object will
76be serialized and stored in a text file on your server. Subsequent calls to that query will use the result from the cache file
77rather then accessing your database. In other words, the first time a page is loaded a cache file will be written.
78The next time the page is loaded the cached file will be used.</p>
admin43a823e2006-09-27 01:57:10 +0000[diff] [blame]79
admin11c06c72006-10-05 05:12:27 +0000[diff] [blame]80<p>When a "write" type query (INSERT, UPDATE, etc.) is run , any cache files associated with the particular page being viewed
adminf3428b52006-10-05 05:19:15 +0000[diff] [blame^]81will be deleted automatically. If you need to update some data with every page load (user stats, for example) you will
82need to manually disable caching just before running your "write" query, then re-enable it just
83after. Otherwise, your site will be caught in a cycle of writing/deleting caches with every page view, creating more load then if you were not using
admin11c06c72006-10-05 05:12:27 +0000[diff] [blame]84caching. More information on this will be found below.</p>
admin43a823e2006-09-27 01:57:10 +0000[diff] [blame]85
admin43a823e2006-09-27 01:57:10 +0000[diff] [blame]86
admin11c06c72006-10-05 05:12:27 +0000[diff] [blame]87<p>Although caching will reduce your database load, dealing with cache files does generate more
88up-front processing and file-system operations, as cache files are created and read. Instead of accessing your database for information
89text files are used.</p>
admin43a823e2006-09-27 01:57:10 +0000[diff] [blame]90
admin11c06c72006-10-05 05:12:27 +0000[diff] [blame]91<p>Whether you see a performance gain as a result of caching is dependant on many factors.
admin5ffba1e2006-10-05 04:23:18 +0000[diff] [blame]92For example, if you have a highly optimized database under very little load, you probably won't see a performance boost.
93If your database is under heavy use you probably will see an improved response, assuming your filesystem is not
admin11c06c72006-10-05 05:12:27 +0000[diff] [blame]94overly taxed. In some clustered server environments caching may be detrimental since filesystem operations are so intense.
95On single servers (particularly in shared enironments) caching will probably be beneficial. Unfortunately there is no
96single answer to the question of whether you should cache your database. It really depends on your situation.</p>
admin43a823e2006-09-27 01:57:10 +0000[diff] [blame]97
admin11c06c72006-10-05 05:12:27 +0000[diff] [blame]98<h2>Enabling Caching</h2>
99
100<p>Enabling caching requires three steps:</p>
101
102<ul>
103<li>Creating a directory on your server where the cache files will be written.</li>
104<li>Setting the path to your cache folder in your <dfn>application/config/database.php</dfn> file.</li>
105<li>Enalbling the caching preference either in your database config file or manually in your controllers.</li>
106</ul>
admin43a823e2006-09-27 01:57:10 +0000[diff] [blame]107
108
adminf3428b52006-10-05 05:19:15 +0000[diff] [blame^]109<h2>Caching Example</h2>
110
111<p>Here is an example showing how you can selectively cache some queries and not others. Notice that the "write" type queries
112are not.
113
114<code>
115<kbd>$this->db->cache_on();</kbd> // Turns on caching. We assume that you've set up a valid cache foler...
116
117$query = $this->db->query("SELECT * FROM blog LIMIT 10);
118
119foreach ($query->result() as $row)
120{
121 echo '<h3>'.$row->title.'</h3>';
122 echo '<p>'>.$row->content.'</p>';
123}
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