Re: Stats for multi-column indexes

Josh Berkus <josh@agliodbs.com> writes:
>> Actually, I think you don't particularly need stats for that in most
>> cases --- if the planner simply took note that the FK relationship
>> exists, it would know that each row of the FK side joins to exactly
>> one row of the PK side, which in typical cases is sufficient.

> Is it?  What about the other direction?

I recall that we had decided at the Greenplum meeting last year that
we could use a better heuristic if we noted that a join was being done
on an FK-and-PK combination, but I don't recall the details right at
the moment.  Did anyone take notes?
        regards, tom lane