Re: Avoiding hash join batch explosions with extreme skew and weird stats

On 29/04/2020 05:03, Melanie Plageman wrote:
> I've attached a patch which should address some of the previous feedback
> about code complexity. Two of my co-workers and I wrote what is
> essentially a new prototype of the idea. It uses the main state machine
> to route emitting unmatched tuples instead of introducing a separate
> state. The logic for falling back is also more developed.

I haven't looked at the patch in detail, but thanks for the commit
message; it describes very well what this is all about. It would be nice
to copy that explanation to the top comment in nodeHashJoin.c in some
form. I think we're missing a high level explanation of how the batching
works even before this new patch, and that commit message does a good
job at it.