Re: No hash join across partitioned tables?

Did this get addressed?

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Tom Lane wrote:
> Kris Jurka <books(at)ejurka(dot)com> writes:
> > The real problem is getting reasonable stats to pass through the partition
> > Append step, so it can make a reasonable estimate of the join output size.
>
> I dug around a bit and concluded that the lack of stats for the Append
> relation is indeed the main problem. It's not so much the bad join size
> estimate (although that could hurt for cases where you need to join this
> result to another table). Rather, it's that the planner is deliberately
> biased against picking hash joins in the absence of stats for the inner
> relation. Per the comments for estimate_hash_bucketsize:
>
> * If no statistics are available, use a default estimate of 0.1. This will
> * discourage use of a hash rather strongly if the inner relation is large,
> * which is what we want. We do not want to hash unless we know that the
> * inner rel is well-dispersed (or the alternatives seem much worse).
>
> While we could back off the default a bit here, I think it'd be better
> to fix it by not punting on the stats-for-append-relations problem.
> That doesn't seem like material for 8.4 at this point, though.
>
> regards, tom lane
>
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