[knightni]

Oracle and DB2 both offer ways to provide hints to the database about how you want the query processed, and the ability to store those hints independently of the query - Stored Outlines and Plan Stability being the features in question. This is particularly useful when you can't risk the plan changing in production and screwing you over - in that situation it's preferable to experience a gradual degradation->optimisation cycle personally.

It's one thing that I find it frustrating that Postgres (which I otherwise love) doesn't offer - I understand that they don't like optimiser hints, but at least the ability to say 'keep using the current plan until I give you permission to do otherwise' would be invaluable.