Database caching confusion

[eluser]blowmenow[/eluser]
Hi there folks.
Ive got a very serious problem. I cannot see a deferents between those snippets:

Code:

$this->db->cache_on();

and

Code:

$this->db->start_cache();

I'm really confused, are there many types of database caching? Or it is just redundant code? Explain it to me. Thank you!.