Mike Harding <mvh(at)ix(dot)netcom(dot)com> writes:
> I've been having problems where a HashAggregate is used because of a bad
> estimate of the distinct number of elements involved.
If you're desperate, there's always enable_hashagg. Or reduce sort_mem
enough so that even the misestimate looks like it will exceed sort_mem.
In the long run it would be nice if HashAgg could spill to disk. We
were expecting to see a contribution of code along that line last year
(from the CMU/Berkeley database class) but it never showed up. The
performance implications might be a bit grim anyway :-(
regards, tom lane