On Wed, 5 Dec 2001, [iso-8859-1] DI Hasen�hrl wrote:
> Thank you for your response, but I'm not quite clear.
>
> Is *sort_mem* the same as postgres' starting option -S *Sortsize*,
> which is by default 512Kb
> At this time I increased sortsize to 1024Kb, but the costs from
> explain are the same as before and I can't see, that the query is
> faster
IIRC the explain costs may not change. If your table really only
has 4000 rows, I don't see why it would need to drop off to disk,
but while the query is running, you can see if pg_sorttemp* files
are being created under your data directory (which would show
that it is going out to disk and that you may need to raise -S
again). Otherwise, is the data involved something you can share?
It might help for us to be able to try it elsewhere to see how
it performs.
> Please, can you explain, what *cost=341.63..341.63* means
It's an estimate of cost. I believe the first is startup cost
and the last total cost. You probably want to read the performance
tips section of the user's guide.
