Quan Zongliang <quanzongli...@yeah.net> writes: > Perhaps we should discard this (dups cnt > 1) restriction?
That's not going to happen on the basis of one test case that you haven't even shown us. The implications of doing it are very unclear. In particular, I seem to recall that there are bits of logic that depend on the assumption that MCV entries always represent more than one row. The nmultiple calculation Tomas referred to may be failing because of that, but I'm worried about there being other places. Basically, you're proposing a rather fundamental change in the rules by which Postgres has gathered statistics for decades. You need to bring some pretty substantial evidence to support that. The burden of proof is on you, not on the status quo. regards, tom lane