Re: 8.4 optimization regression?

Mark Kirkwood <mark.kirkwood@catalyst.net.nz> writes:
> While this is still fresh in your mind, a couple of additional anti join
> queries are still managing to sneak past estimation:

Yeah, those are estimating that all the outer rows have join partners,
because there are more distinct values in the sub-select than there are
in the outer relation.  AFAICS there are not any errors in the
statistics, it's just that the estimation rule falls down here.

If you've heard of a better estimator for semijoin/antijoin selectivity,
I'm all ears.  The best idea I have at the moment is to put an arbitrary
upper limit on the estimated selectivity, but that would be, well,
arbitrary.

            regards, tom lane