Tomas Vondra <tomas.von...@2ndquadrant.com> writes: > When it comes to improving multiple (multi-column) foreign keys, I think > it may get way more complicated that it might seem. What if the foreign > keys overlap, for example? Or what if the keys go in opposite directions > (cycle). And so on ...
I think you can group all FKs referencing the same table and discard all their matched join clauses in favor of a single 1/N estimate (and when I say "discard", that means you don't match those clauses against later FKs, which should take care of the reciprocal-FK issue). This is clearly correct if no nulls are involved. We need to make some estimate of how much to de-rate that figure for nulls, but I don't see that it's any harder than what's already required for a single multicol FK. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers