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.
+
+Also note: 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();
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