CodeIgniter supports flashdata - data that is only available for one server request, and then removed. Flash data is very useful, and is usually used for informational messages such as "You hava been logged out" or "Removed user account". Flash variable are prefixed with flash_.

num_rows() function will return the total number of rows returned from a query.
num_fields() function will return the number of fields returned by the query.

It enables us to save a query for use later on in our script execution. Usually, an SQL query is reset after it has been completed. With Active Record cashing we can prevent this reset and reuse queries easily.