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| author | Derek Jones <derek.jones@ellislab.com> | 2011-10-05 20:34:52 +0200 |
|---|---|---|
| committer | Derek Jones <derek.jones@ellislab.com> | 2011-10-05 20:34:52 +0200 |
| commit | 8ede1a2ecbb62577afd32996956c5feaf7ddf9b6 (patch) | |
| tree | 2e960ec3b416b477f40bb546371f2d486f4a22f0 /user_guide/database/caching.html | |
| parent | d1ecd5cd4ae6ab5d37df9fbda14b93977b9e743c (diff) | |
replacing the old HTML user guide with a Sphinx-managed user guide
Diffstat (limited to 'user_guide/database/caching.html')
| -rw-r--r-- | user_guide/database/caching.html | 220 |
1 files changed, 0 insertions, 220 deletions
diff --git a/user_guide/database/caching.html b/user_guide/database/caching.html deleted file mode 100644 index 16d380f5f..000000000 --- a/user_guide/database/caching.html +++ /dev/null @@ -1,220 +0,0 @@ -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> -<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> -<head> - -<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> -<title>Database Caching Class : CodeIgniter User Guide</title> - -<style type='text/css' media='all'>@import url('../userguide.css');</style> -<link rel='stylesheet' type='text/css' media='all' href='../userguide.css' /> - -<script type="text/javascript" src="../nav/nav.js"></script> -<script type="text/javascript" src="../nav/prototype.lite.js"></script> -<script type="text/javascript" src="../nav/moo.fx.js"></script> -<script type="text/javascript" src="../nav/user_guide_menu.js"></script> - -<meta http-equiv='expires' content='-1' /> -<meta http-equiv= 'pragma' content='no-cache' /> -<meta name='robots' content='all' /> -<meta name='author' content='ExpressionEngine Dev Team' /> -<meta name='description' content='CodeIgniter User Guide' /> - -</head> -<body> - -<!-- START NAVIGATION --> -<div id="nav"><div id="nav_inner"><script type="text/javascript">create_menu('../');</script></div></div> -<div id="nav2"><a name="top"></a><a href="javascript:void(0);" onclick="myHeight.toggle();"><img src="../images/nav_toggle_darker.jpg" width="154" height="43" border="0" title="Toggle Table of Contents" alt="Toggle Table of Contents" /></a></div> -<div id="masthead"> -<table cellpadding="0" cellspacing="0" border="0" style="width:100%"> -<tr> -<td><h1>CodeIgniter User Guide Version 2.0.3</h1></td> -<td id="breadcrumb_right"><a href="../toc.html">Table of Contents Page</a></td> -</tr> -</table> -</div> -<!-- END NAVIGATION --> - - -<!-- START BREADCRUMB --> -<table cellpadding="0" cellspacing="0" border="0" style="width:100%"> -<tr> -<td id="breadcrumb"> -<a href="http://codeigniter.com/">CodeIgniter Home</a> › -<a href="../index.html">User Guide Home</a> › -<a href="index.html">Database Library</a> › -Database Caching Class -</td> -<td id="searchbox"><form method="get" action="http://www.google.com/search"><input type="hidden" name="as_sitesearch" id="as_sitesearch" value="codeigniter.com/user_guide/" />Search User Guide <input type="text" class="input" style="width:200px;" name="q" id="q" size="31" maxlength="255" value="" /> <input type="submit" class="submit" name="sa" value="Go" /></form></td> -</tr> -</table> -<!-- END BREADCRUMB --> - - -<br clear="all" /> - - -<!-- START CONTENT --> -<div id="content"> - -<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> 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> 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() / $this->db->cache_off()</h2> - -<p>Manually enables/disables caching. This can be useful if you want to -keep certain queries from being cached. Example:</p> - -<code> -// Turn caching on<br /> -$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> - - - - - - - - - - -</div> -<!-- END CONTENT --> - - -<div id="footer"> -<p> -Previous Topic: <a href="call_function.html">Custom Function Calls</a> - · -<a href="#top">Top of Page</a> · -<a href="../index.html">User Guide Home</a> · -Next Topic: <a href="forge.html">Database manipulation with Database Forge</a> -</p> -<p><a href="http://codeigniter.com">CodeIgniter</a> · Copyright © 2006 - 2011 · <a href="http://ellislab.com/">EllisLab, Inc.</a></p> -</div> - -</body> -</html>
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