Solving unknown database performance problems

[Going to Cali]

A system that uses an oracle backend has performance issues. Assuming there's no infrastructure faults, where do you start diagnosing where the fault has occured? (In Oracle) I know of the v$locks and v$sessions table but aside from studying these, removing locks and killing running oracle processes, my diagnosis knowledge is limited. Can someone who has experience in this area help out? Thanks.

 

[Haircut]

I'd ask a DBA to have a look into it.

DBMS_STATS is the preferred option these days as far as I know, but it's not really the sort of thing your average developer will have too much knowledge about.
http://www.dba-oracle.com/art_builder_dbms_stats.htm

 

[uv]

Locks are there for a reason, you shouldn't go around killing locks. Heck, your account shouldn't be granted the ability to kill locks, this should be for DBAs only.

Killing locks off can just end up in your database getting a deadlock.