Re: Question with hashed IN

On Sat, 16 Aug 2003, Stephan Szabo wrote:

>
> I've noticed that when the stats are wrong (like
> in cases where you've loaded data but reltuples
> hasn't been updated yet) that a hashed NOT IN
> seems to take a significant time penalty. Is
> this to be expected?
>
> On a pktest table with 1 million integers and a dual table with a single
> integer and sort_mem set high enough to give a hashed subplan for the
> various reltuples values, I saw the following behavior for
>
> explain analyze select * from dual where a not in (select a from pktest);
>
> with reltuples=1000 for pktest, query takes about 96 seconds
> reltuples=10000, query takes about 15 seconds
> reltuples=100000, query takes about 8 seconds
>
> And the memory usage seemed to be the same even if I set sort_mem back
> to 1024.

Errm, I meant in the cases where it still chose a hashed
subplan. Stupid cold medicine.