Re: Design notes for EquivalenceClasses

Gavin Sherry <swm(at)linuxworld(dot)com(dot)au> writes:
> I was thinking about this, but in relation to hash joins. A hash join
> cannot be guaranteed to produce output sorted according to the pathkey of
> the outer relation (as explained in the existing README). I wonder,
> however, if it might be useful for hash join to pass a hint that the
> output is known ordered (i.e., the join was not split into multiple
> batches).

Yeah, I've considered that, but I think it'd have to be the other way
around: the planner tells the executor that it's assuming the output is
sorted, hence do not split into multiple batches. This has the usual
assortment of problems if the planner has badly misestimated the
rowcount :-(

regards, tom lane