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| <td><h1>Code Igniter User Guide Version 1.5.0</h1></td> | |
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| <h1>Database Caching Class</h1> | |
| <p>The Database Caching Class contains functions that permit you to cache your queries.</p> | |
| <p class="important"><strong>Important:</strong> This class is initialized automatically by the database driver | |
| when caching is enabled. Do NOT load this class manually. | |
| More info below...</p> | |
| <h2>How Does Caching Work?</h2> | |
| <p>When caching is enabled, anytime a "read" type query (SELECT) is run, the result object will | |
| be serialized and stored in a text file on your server. Subsequent calls to that query will use the result from the cache file | |
| rather then accessing your database. In other words, the first time a page is loaded a cache file will be written. | |
| The next time the page is loaded the cached file will be used.</p> | |
| <p>When a "write" type query (INSERT, UPDATE, etc.) is run , any cache files associated with the particular page being viewed | |
| will be deleted automatically. If you need to update some data with every page load (user stats, for example) you will | |
| need to manually disable caching just before running your "write" query, then re-enable it just | |
| after. 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 | |
| caching. More information on this will be found below.</p> | |
| <p>Although caching will reduce your database load, dealing with cache files does generate more | |
| up-front processing and file-system operations, as cache files are created and read. Instead of accessing your database for information | |
| text files are used.</p> | |
| <p>Whether you see a performance gain as a result of caching is dependant on many factors. | |
| For example, 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 filesystem is not | |
| overly taxed. In some clustered server environments caching may be detrimental since filesystem operations are so intense. | |
| On single servers (particularly in shared enironments) 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>Enabling Caching</h2> | |
| <p>Enabling caching requires three steps:</p> | |
| <ul> | |
| <li>Creating a directory on your server where the cache files will be written.</li> | |
| <li>Setting the path to your cache folder in your <dfn>application/config/database.php</dfn> file.</li> | |
| <li>Enalbling the caching preference either in your database config file or manually in your controllers.</li> | |
| </ul> | |
| <h2>Caching Example</h2> | |
| <p>Here is an example showing how you can selectively cache some queries and not others. Notice that the "write" type queries | |
| are not. | |
| <code> | |
| // Turn OFF caching for this one query since we don't<br /> | |
| // want it to affect any existing cache files<br /> | |
| <kbd>$this->db->cache_off();</kbd><br /> | |
| <br /> | |
| $this->db->query("UPDATE web_stats SET page_views = page_views + 1");<br /> | |
| <br /><br /> | |
| // Re-enable caching<br /> | |
| <kbd>$this->db->cache_on();</kbd> <br /> | |
| <br /> | |
| $query = $this->db->query("SELECT * FROM blog LIMIT 10");<br /> | |
| <br /> | |
| foreach ($query->result() as $row)<br /> | |
| {<br /> | |
| echo '<h3>'.$row->title.'</h3>';<br /> | |
| echo '<p>'>.$row->content.'</p>';<br /> | |
| }<br /> | |
| <br /> | |
| $query = $this->db->query("SELECT page_views FROM web_stats");<br /> | |
| $row = $query->row();<br /> | |
| <br /> | |
| echo '<p>'.$row->page_views.'</p>';<br /> | |
| <br /> | |
| // Update the web stats, so we turn off caching so that the cache<br /> | |
| // file for the above query doesn't get deleted<br /> | |
| <br /> | |
| </code> | |
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