Re: NOT IN query takes forever

On Tue, 2004-08-03 at 10:10, Merlin Moncure wrote:
> > > Try bumping up shared buffers some and sort mem as much as you
> safely
> > > can.
> > Thank you, that did it!
> >
> > With
> > shared_buffers = 3000 # min 16, at least max_connections*2,
> 8KB
> > each
> > sort_mem = 128000 # min 64, size in KB
> >
> > it takes <3 seconds (my hardware is not server-class).
>
> Be careful...sort_mem applies to each connection and (IIRC) in some
> cases more than once to a connection. Of all the configuration
> parameters, sort_mem (IMO) is the most important and the hardest to get
> right. 128k (or 128MB) is awfully high unless you have a ton of memory
> (you don't) or you are running in single connection scenarios. Do some
> experimentation by lowering the value until you get a good balance
> between potential memory consumption and speed.

Minor nit, sort_mem actually applies to EACH sort individually, so a
query that had to run three sorts could use 3 x sort_mem.

Note that one can set sort_mem per backend connection with set
sort_mem=128000 if need be so as not to use up all the memory with other
backends.