Re: [BUG?] estimate_hash_bucket_stats uses wrong ndistinct for avgfreq

Tender Wang <tndrwang(at)gmail(dot)com> writes:
> In my previous email， I worried rel->tuples may be zero for an empty relation.
> But here it's safe, because an empty relation has no tuples in pg_statistic.

Not sure about that --- it seems possible that after a mass delete,
VACUUM could update pg_class.reltuples to zero without touching
pg_statistic. And I also don't remember whether the planner clamps
rel->tuples to be at least 1. But it doesn't matter. If rel->tuples
is zero, the if-test will prevent us from dividing by zero, and then
we'll leave *mcv_freq as zero meaning "unknown", which seems fine.
It's the same thing that would have happened before bd3e3e9e5.

regards, tom lane