Re: Why hash join instead of nested loop?

Well that could be an issue, is this abnormally large:

#shared_buffers = 1536          # min 16, at least max_connections*2, 8KB each
shared_buffers = 206440
#sort_mem = 131072              # min 64, size in KB
sort_mem = 524288               # min 64, size in KB
vacuum_mem = 131072             # min 1024, size in K

I actually had a lot of trouble finding example values for these... no
one wants to give real numbers in any postgres performance tuning
articles I saw. What would be appropriate for machines with 1 or 6
gigs of RAM and wanting to maximize performance.

Rhett

On 8/9/05, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Rhett Garber <rhettg@gmail.com> writes:
> > They are both running SuSE 8, 2.4.21-128-smp kernel
>
> > Compile instructions (I didn't do it myself) indicate we built from
> > source with nothing fancy:
>
> You could double-check the configure options by running pg_config.
> But probably the more interesting question is whether any nondefault
> CFLAGS were used, and I don't think pg_config records that.
> (Hmm, maybe it should.)
>
> In any case, there's no smoking gun there.  I'm now wondering if maybe
> there's something unusual about your runtime parameters.  AFAIR you
> didn't show us your postgresql.conf settings --- could we see any
> nondefault entries there?
>
> (I looked quickly at the 7.4 hashjoin code, and I see that it uses a
> hash table sized according to sort_mem even when the input is predicted
> to be very small ... so an enormous sort_mem setting would account for
> some plan startup overhead to initialize the table ...)
>
>                         regards, tom lane
>