Re: Weird 8.2.4 performance

Kurt Overberg <kurt@hotdogrecords.com> writes:
> ... Turning off bitmap scans definitely seems
> to help things,

I really seriously doubt that.  On queries like this, where each inner
scan is fetching a couple hundred rows, the small extra overhead of a
bitmap scan should easily pay for itself.  I think you're looking
entirely at caching effects that allow a re-read of the same data to
go faster.

You might try running the same query plan several times in a row and
noting the lowest time, then repeat for the other query plan.  This will
get you comparable fully-cached times, which I bet will be very close
to the same.

            regards, tom lane