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+######################
+Database Caching Class
+######################
+
+The Database Caching Class permits you to cache your queries as text
+files for reduced database load.
+
+.. important:: This class is initialized automatically by the database
+	driver when caching is enabled. Do NOT load this class manually.
+
+.. important:: Not all query result functions are available when you
+	use caching. Please read this page carefully.
+
+Enabling Caching
+================
+
+Caching is enabled in three steps:
+
+-  Create a writable directory on your server where the cache files can
+   be stored.
+-  Set the path to your cache folder in your
+   application/config/database.php file.
+-  Enable the caching feature, either globally by setting the preference
+   in your application/config/database.php file, or manually as
+   described below.
+
+Once enabled, caching will happen automatically whenever a page is
+loaded that contains database queries.
+
+How Does Caching Work?
+======================
+
+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.
+
+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.
+
+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.
+
+Will Caching Improve Your Site's Performance?
+=============================================
+
+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.
+
+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.
+
+How are Cache Files Stored?
+===========================
+
+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).
+
+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.
+
+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.
+
+Managing your Cache Files
+=========================
+
+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.
+
+Not All Database Functions Work with Caching
+============================================
+
+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.
+
+The following functions ARE NOT available when using a cached result
+object:
+
+-  num_fields()
+-  field_names()
+-  field_data()
+-  free_result()
+
+Also, the two database resources (result_id and conn_id) are not
+available when caching, since result resources only pertain to run-time
+operations.
+
+******************
+Function Reference
+******************
+
+$this->db->cache_on() / $this->db->cache_off()
+================================================
+
+Manually enables/disables caching. This can be useful if you want to
+keep certain queries from being cached. Example::
+
+	 // Turn caching on $this->db->cache_on(); $query = $this->db->query("SELECT * FROM mytable");  // Turn caching off for this one query $this->db->cache_off(); $query = $this->db->query("SELECT * FROM members WHERE member_id = '$current_user'");  // Turn caching back on $this->db->cache_on(); $query = $this->db->query("SELECT * FROM another_table");
+
+$this->db->cache_delete()
+==========================
+
+Deletes the cache files associated with a particular page. This is
+useful if you need to clear caching after you update your database.
+
+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::
+
+	$this->db->cache_delete('blog', 'comments');
+
+If you do not use any parameters the current URI will be used when
+determining what should be cleared.
+
+$this->db->cache_delete_all()
+===============================
+
+Clears all existing cache files. Example::
+
+	$this->db->cache_delete_all();
+