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Diffstat (limited to 'user_guide/database/caching.html')
| -rw-r--r-- | user_guide/database/caching.html | 103 |
1 files changed, 45 insertions, 58 deletions
diff --git a/user_guide/database/caching.html b/user_guide/database/caching.html index 1ee0b19b8..8bf534352 100644 --- a/user_guide/database/caching.html +++ b/user_guide/database/caching.html @@ -64,86 +64,73 @@ Database Caching Class <h1>Database Caching Class</h1>
-<p>The Database Caching Class contains functions that permit you to cache your queries.</p>
+<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> This class is initialized automatically by the database driver
-when caching is enabled. Do NOT load this class manually.
-More info below...</p>
+when caching is enabled. Do NOT load this class manually.<br /><br />
+
+<strong>Also note:</strong> 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>
+
<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>Code Igniter's query caching system happens dynamically when your pages are viewed.
+When caching is enabled, the first time a webpage 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>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>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 does
+have an "auto-delete"feature, as described below. It also lets you manually clear caches associated with individulal pages, or
+you can delete the entire collection of cache files.</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>
+<h2>Will Caching Improve Your Site's Performance?</h2>
-<p>Whether you see a performance gain as a result of caching is dependant on many factors.
+<p>Maybe. Whether you see a performance gain as a result of caching depends 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.
+overly taxed. Remember that caching simply changes how your information is retrieved, shifting it from being a database
+operation to a filesystem one.</p>
+
+<p>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>
+<h2>How are Cache Files Stored?</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.
+<p>Code Igniter places the result of EACH query into its own cache file. Sets of cache files are further organized into
+sub-folders corrsponding to your controller functions.</p>
-<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 />
+<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>
-// 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 />
+<p>If your have dynamic queries that change based on inormation 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>
-</code>
+<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>
+<h1>Function Reference</h1>
|