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| <div class="section" id="database-caching-class"> |
| <h1>Database Caching Class<a class="headerlink" href="#database-caching-class" title="Permalink to this headline">¶</a></h1> |
| <p>The Database Caching Class permits you to cache your queries as text |
| files for reduced database load.</p> |
| <div class="admonition important"> |
| <p class="first admonition-title">Important</p> |
| <p class="last">This class is initialized automatically by the database |
| driver when caching is enabled. Do NOT load this class manually.</p> |
| </div> |
| <div class="admonition important"> |
| <p class="first admonition-title">Important</p> |
| <p class="last">Not all query result functions are available when you |
| use caching. Please read this page carefully.</p> |
| </div> |
| <div class="section" id="enabling-caching"> |
| <h2>Enabling Caching<a class="headerlink" href="#enabling-caching" title="Permalink to this headline">¶</a></h2> |
| <p>Caching is enabled in three steps:</p> |
| <ul class="simple"> |
| <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 |
| application/config/database.php file.</li> |
| <li>Enable the caching feature, either globally by setting the preference |
| in your application/config/database.php 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> |
| </div> |
| <div class="section" id="how-does-caching-work"> |
| <h2>How Does Caching Work?<a class="headerlink" href="#how-does-caching-work" title="Permalink to this headline">¶</a></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 read-type (SELECT) queries can be cached, since these are the only |
| type of queries that produce a result. Write-type (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> |
| </div> |
| <div class="section" id="will-caching-improve-your-site-s-performance"> |
| <h2>Will Caching Improve Your Site’s Performance?<a class="headerlink" href="#will-caching-improve-your-site-s-performance" title="Permalink to this headline">¶</a></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> |
| </div> |
| <div class="section" id="how-are-cache-files-stored"> |
| <h2>How are Cache Files Stored?<a class="headerlink" href="#how-are-cache-files-stored" title="Permalink to this headline">¶</a></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 blog with a function |
| called comments that contains three queries. The caching system will |
| create a cache folder called blog+comments, 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> |
| </div> |
| <div class="section" id="managing-your-cache-files"> |
| <h2>Managing your Cache Files<a class="headerlink" href="#managing-your-cache-files" title="Permalink to this headline">¶</a></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> |
| </div> |
| <div class="section" id="not-all-database-functions-work-with-caching"> |
| <h2>Not All Database Functions Work with Caching<a class="headerlink" href="#not-all-database-functions-work-with-caching" title="Permalink to this headline">¶</a></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 ARE NOT available when using a cached result |
| object:</p> |
| <ul class="simple"> |
| <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> |
| <div class="section" id="function-reference"> |
| <h3>Function Reference<a class="headerlink" href="#function-reference" title="Permalink to this headline">¶</a></h3> |
| </div> |
| </div> |
| <div class="section" id="this-db-cache-on-this-db-cache-off"> |
| <h2>$this->db->cache_on() / $this->db->cache_off()<a class="headerlink" href="#this-db-cache-on-this-db-cache-off" title="Permalink to this headline">¶</a></h2> |
| <p>Manually enables/disables caching. This can be useful if you want to |
| keep certain queries from being cached. Example:</p> |
| <div class="highlight-ci"><div class="highlight"><pre><span></span><span class="c1">// Turn caching on</span> |
| <span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">cache_on</span><span class="p">();</span> |
| <span class="nv">$query</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">query</span><span class="p">(</span><span class="s2">"SELECT * FROM mytable"</span><span class="p">);</span> |
| |
| <span class="c1">// Turn caching off for this one query</span> |
| <span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">cache_off</span><span class="p">();</span> |
| <span class="nv">$query</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">query</span><span class="p">(</span><span class="s2">"SELECT * FROM members WHERE member_id = '</span><span class="si">$current_user</span><span class="s2">'"</span><span class="p">);</span> |
| |
| <span class="c1">// Turn caching back on</span> |
| <span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">cache_on</span><span class="p">();</span> |
| <span class="nv">$query</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">query</span><span class="p">(</span><span class="s2">"SELECT * FROM another_table"</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| </div> |
| <div class="section" id="this-db-cache-delete"> |
| <h2>$this->db->cache_delete()<a class="headerlink" href="#this-db-cache-delete" title="Permalink to this headline">¶</a></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 example.com/index.php/blog/comments, the caching system will put |
| all cache files associated with it in a folder called blog+comments. To |
| delete those particular cache files you will use:</p> |
| <div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">cache_delete</span><span class="p">(</span><span class="s1">'blog'</span><span class="p">,</span> <span class="s1">'comments'</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>If you do not use any parameters the current URI will be used when |
| determining what should be cleared.</p> |
| </div> |
| <div class="section" id="this-db-cache-delete-all"> |
| <h2>$this->db->cache_delete_all()<a class="headerlink" href="#this-db-cache-delete-all" title="Permalink to this headline">¶</a></h2> |
| <p>Clears all existing cache files. Example:</p> |
| <div class="highlight-ci"><div class="highlight"><pre><span></span><span class="nv">$this</span><span class="o">-></span><span class="na">db</span><span class="o">-></span><span class="na">cache_delete_all</span><span class="p">();</span> |
| </pre></div> |
| </div> |
| </div> |
| </div> |
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