Rajesh Kumar Mallah <mallah@trade-india.com> writes:
> NOT EXISTS is taking almost double time than NOT IN .
> I know IN has been optimised in 7.4 but is anything
> wrong with the NOT EXISTS?
That's the expected behavior in 7.4. EXISTS in the style you are using
it effectively forces a nestloop-with-inner-indexscan implementation.
As of 7.4, IN can do that, but it can do several other things too,
including the hash-type plan you have here. So assuming that the
planner chooses the right plan choice (not always a given ;-))
IN should be as fast or faster than EXISTS in all cases.
regards, tom lane