Re: Any way to optimize GROUP BY queries?

"Jim C. Nasby" <jnasby@pervasive.com> writes:
> On Mon, Dec 19, 2005 at 03:47:35PM -0500, Greg Stark wrote:
>> Increase your work_mem (or sort_mem in older postgres versions), you can do
>> this for the server as a whole or just for this one session and set it back
>> after this one query. You can increase it up until it starts causing swapping
>> at which point it would be counter productive.

> Just remember that work_memory is per-operation, so it's easy to push
> the box into swapping if the workload increases. You didn't say how much
> memory you have, but I'd be careful if work_memory * max_connections
> gets very much larger than your total memory.

It's considered good practice to have a relatively small default
work_mem setting (in postgresql.conf), and then let individual sessions
push up the value locally with "SET work_mem" if they are going to
execute queries that need it.  This works well as long as you only have
one or a few such "heavy" sessions at a time.

            regards, tom lane