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
