Andres Freund <and...@anarazel.de> writes:
> Not sure I follow. Unless the values are equivalent (i.e. duplicate key
> values), why should non-uniformity in key space translate to hash space?
Duplicates are exactly the problem. See estimate_hash_bucket_stats.
> And if there's duplicates it shouldn't hurt much either, unless doing
> a semi/anti-join? All rows are going to be returned and IIRC we quite
> cheaply continue a bucket scan?
If the bucket containing the MCV is bigger than work_mem, you gotta
problem --- one not necessarily shared by the other relation.
regards, tom lane
