Re: No hash join across partitioned tables?

On Thu, 16 Apr 2009, Tom Lane wrote:

> Kris Jurka <books(at)ejurka(dot)com> writes:
>> PG (8.3.7) doesn't seem to want to do a hash join across two partitioned
>> tables.
>
> Could we see the whole declaration of these tables? (pg_dump -s output
> would be convenient)
>

The attached table definition with no data wants to mergejoin first, but
after disabling mergejoin it does indeed do a hashjoin.

Looking back at the cost estimates for the merge and nestloop joins, it
seems to be selecting the number of rows in the cartesian product * .005
while the number of output rows in this case is 2437 (cartesian product *
4e-9). Perhaps the cost estimates for the real data are so high because
of this bogus row count that the fudge factor to disable mergejoin isn't
enough?

Kris Jurka