after i have finished with my result set from a active record query in a CodeIgniter model, should I use
$query->free_result() or does ActiveRecord automatically do that?
PHP will clean up everything after your script is done. However, if you have lots of queries in, say, a loop, the results will not be cleaned up after each iteration.
So, if you run lots of queries in a loop, you probably will want to free_result() to clear up memory. Otherwise, it's not necessary. See here for details: