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diff --git a/user_guide_src/source/database/caching.rst b/user_guide_src/source/database/caching.rst deleted file mode 100644 index d73120a93..000000000 --- a/user_guide_src/source/database/caching.rst +++ /dev/null @@ -1,162 +0,0 @@ -###################### -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(); - |