Re: Why this Query Plan is different

"Thilina Gunasekara" <tgunasekara@openworld.org> writes:
> I have two PostgreSQL Database Servers running on Gentoo which versions are
> PostgreSQL 7.4.5 (Box A) and PostgreSQL 7.3.9 (Box B)
> Due to a recent query posted by a developer I was interested to know which
> factors are affecting these two servers to behave in a different manner to
> the same query. Please shed light on this.

7.4 knows a great deal more about optimizing IN queries than 7.3 does.
I think you have misidentified the two query plans, because "Hash IN
Join" is not a plan type that 7.3 has at all.  What is not clear to me
is which version is really slower.  Could we see EXPLAIN ANALYZE output
(correctly labeled ;-)) not just EXPLAIN?

            regards, tom lane