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authorAndrey Andreev <narf@devilix.net>2018-01-13 12:57:11 +0100
committerAndrey Andreev <narf@devilix.net>2018-01-13 12:57:11 +0100
commit02a0518e1c56ba3506f370362ac5ebdb8a138312 (patch)
tree8b4684192b403dcae17d298eb4fc9e7ab001acad /user_guide/database/caching.html
parentf0b9735d5857e6c07c8f5824b13cff4828db3cfe (diff)
[ci skip] 3.1.7 release
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+<li class="toctree-l2"><a class="reference internal" href="../overview/mvc.html">Model-View-Controller</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../overview/goals.html">Architectural Goals</a></li>
+</ul>
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+<li class="toctree-l1"><a class="reference internal" href="../tutorial/index.html">Tutorial</a><ul>
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+<li class="toctree-l2"><a class="reference internal" href="../tutorial/create_news_items.html">Create news items</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../tutorial/conclusion.html">Conclusion</a></li>
+</ul>
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+<li class="toctree-l1"><a class="reference internal" href="../contributing/index.html">Contributing to CodeIgniter</a><ul>
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+<li class="toctree-l2"><a class="reference internal" href="../DCO.html">Developer’s Certificate of Origin 1.1</a></li>
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+<ul>
+<li class="toctree-l1"><a class="reference internal" href="../general/index.html">General Topics</a><ul>
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+<li class="toctree-l2"><a class="reference internal" href="../general/views.html">Views</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/models.html">Models</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/helpers.html">Helpers</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/libraries.html">Using CodeIgniter Libraries</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/creating_libraries.html">Creating Libraries</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/drivers.html">Using CodeIgniter Drivers</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/creating_drivers.html">Creating Drivers</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/core_classes.html">Creating Core System Classes</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/ancillary_classes.html">Creating Ancillary Classes</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/hooks.html">Hooks - Extending the Framework Core</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/autoloader.html">Auto-loading Resources</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/common_functions.html">Common Functions</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/compatibility_functions.html">Compatibility Functions</a></li>
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+<li class="toctree-l2"><a class="reference internal" href="../general/errors.html">Error Handling</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/caching.html">Caching</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/profiling.html">Profiling Your Application</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/cli.html">Running via the CLI</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/managing_apps.html">Managing your Applications</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/environments.html">Handling Multiple Environments</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/alternative_php.html">Alternate PHP Syntax for View Files</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/security.html">Security</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../general/styleguide.html">PHP Style Guide</a></li>
+</ul>
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+<li class="toctree-l1"><a class="reference internal" href="../libraries/index.html">Libraries</a><ul>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/benchmark.html">Benchmarking Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/caching.html">Caching Driver</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/calendar.html">Calendaring Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/cart.html">Shopping Cart Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/config.html">Config Class</a></li>
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+<li class="toctree-l2"><a class="reference internal" href="../libraries/encryption.html">Encryption Library</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/file_uploading.html">File Uploading Class</a></li>
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+<li class="toctree-l2"><a class="reference internal" href="../libraries/ftp.html">FTP Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/image_lib.html">Image Manipulation Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/input.html">Input Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/javascript.html">Javascript Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/language.html">Language Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/loader.html">Loader Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/migration.html">Migrations Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/output.html">Output Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/pagination.html">Pagination Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/parser.html">Template Parser Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/security.html">Security Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/sessions.html">Session Library</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/table.html">HTML Table Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/trackback.html">Trackback Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/typography.html">Typography Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/unit_testing.html">Unit Testing Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/uri.html">URI Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/user_agent.html">User Agent Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/xmlrpc.html">XML-RPC and XML-RPC Server Classes</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../libraries/zip.html">Zip Encoding Class</a></li>
+</ul>
+</li>
+</ul>
+<ul class="current">
+<li class="toctree-l1 current"><a class="reference internal" href="index.html">Database Reference</a><ul class="current">
+<li class="toctree-l2"><a class="reference internal" href="examples.html">Quick Start: Usage Examples</a></li>
+<li class="toctree-l2"><a class="reference internal" href="configuration.html">Database Configuration</a></li>
+<li class="toctree-l2"><a class="reference internal" href="connecting.html">Connecting to a Database</a></li>
+<li class="toctree-l2"><a class="reference internal" href="queries.html">Running Queries</a></li>
+<li class="toctree-l2"><a class="reference internal" href="results.html">Generating Query Results</a></li>
+<li class="toctree-l2"><a class="reference internal" href="helpers.html">Query Helper Functions</a></li>
+<li class="toctree-l2"><a class="reference internal" href="query_builder.html">Query Builder Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="transactions.html">Transactions</a></li>
+<li class="toctree-l2"><a class="reference internal" href="metadata.html">Getting MetaData</a></li>
+<li class="toctree-l2"><a class="reference internal" href="call_function.html">Custom Function Calls</a></li>
+<li class="toctree-l2 current"><a class="current reference internal" href="#">Query Caching</a></li>
+<li class="toctree-l2"><a class="reference internal" href="forge.html">Database Manipulation with Database Forge</a></li>
+<li class="toctree-l2"><a class="reference internal" href="utilities.html">Database Utilities Class</a></li>
+<li class="toctree-l2"><a class="reference internal" href="db_driver_reference.html">Database Driver Reference</a></li>
+</ul>
+</li>
+</ul>
+<ul>
+<li class="toctree-l1"><a class="reference internal" href="../helpers/index.html">Helpers</a><ul>
+<li class="toctree-l2"><a class="reference internal" href="../helpers/array_helper.html">Array Helper</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../helpers/captcha_helper.html">CAPTCHA Helper</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../helpers/cookie_helper.html">Cookie Helper</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../helpers/date_helper.html">Date Helper</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../helpers/directory_helper.html">Directory Helper</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../helpers/download_helper.html">Download Helper</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../helpers/email_helper.html">Email Helper</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../helpers/file_helper.html">File Helper</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../helpers/form_helper.html">Form Helper</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../helpers/html_helper.html">HTML Helper</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../helpers/inflector_helper.html">Inflector Helper</a></li>
+<li class="toctree-l2"><a class="reference internal" href="../helpers/language_helper.html">Language Helper</a></li>
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+<li class="toctree-l2"><a class="reference internal" href="../helpers/xml_helper.html">XML Helper</a></li>
+</ul>
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+ <li><a href="../index.html">Docs</a> &raquo;</li>
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+ <li><a href="index.html">Database Reference</a> &raquo;</li>
+
+ <li>Database Caching Class</li>
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+
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+ <img title="Classic Layout" alt="classic layout" src="data:image/gif;base64,R0lGODlhFAAUAJEAAAAAADMzM////wAAACH5BAUUAAIALAAAAAAUABQAAAImlI+py+0PU5gRBRDM3DxbWoXis42X13USOLauUIqnlsaH/eY6UwAAOw==" />
+ </div>
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+ <div role="main" class="document">
+
+ <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-&gt;db-&gt;cache_on() / $this-&gt;db-&gt;cache_off()<a class="headerlink" href="#this-db-cache-on-this-db-cache-off" title="Permalink to this headline">¶</a></h2>
+<p>Manually enables/disables caching. This can be useful if you want to
+keep certain queries from being cached. Example:</p>
+<div class="highlight-ci"><div class="highlight"><pre><span></span><span class="c1">// Turn caching on</span>
+<span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</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">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">query</span><span class="p">(</span><span class="s2">&quot;SELECT * FROM mytable&quot;</span><span class="p">);</span>
+
+<span class="c1">// Turn caching off for this one query</span>
+<span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">cache_off</span><span class="p">();</span>
+<span class="nv">$query</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">query</span><span class="p">(</span><span class="s2">&quot;SELECT * FROM members WHERE member_id = &#39;</span><span class="si">$current_user</span><span class="s2">&#39;&quot;</span><span class="p">);</span>
+
+<span class="c1">// Turn caching back on</span>
+<span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">cache_on</span><span class="p">();</span>
+<span class="nv">$query</span> <span class="o">=</span> <span class="nv">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">query</span><span class="p">(</span><span class="s2">&quot;SELECT * FROM another_table&quot;</span><span class="p">);</span>
+</pre></div>
+</div>
+</div>
+<div class="section" id="this-db-cache-delete">
+<h2>$this-&gt;db-&gt;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">$this</span><span class="o">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">cache_delete</span><span class="p">(</span><span class="s1">&#39;blog&#39;</span><span class="p">,</span> <span class="s1">&#39;comments&#39;</span><span class="p">);</span>
+</pre></div>
+</div>
+<p>If you do not use any parameters the current URI will be used when
+determining what should be cleared.</p>
+</div>
+<div class="section" id="this-db-cache-delete-all">
+<h2>$this-&gt;db-&gt;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">-&gt;</span><span class="na">db</span><span class="o">-&gt;</span><span class="na">cache_delete_all</span><span class="p">();</span>
+</pre></div>
+</div>
+</div>
+</div>
+
+
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