Re: Pushing down sorted joins

On Tue, Feb 23, 2016 at 7:48 AM, Ashutosh Bapat
<ashutosh.bapat@enterprisedb.com> wrote:
> Rushabh pointed out that declarations of helper functions
> get_useful_ecs_for_relation and get_useful_pathkeys_for_relation() are part
> of FDW routines declarations rather than helper function declaration. Since
> those functions are related to this patch, the attached patch moves those
> declaration in their right place.

This patch needs to be rebased.

+               /*
+                * TODO: we should worry about EPQ path but should
that path have
+                * pathkeys? I guess, that's not really important
since it's just
+                * going to evaluate the join from whole-row
references stuffed in the
+                * corresponding EPQ slots, for which the order doesn't matter.
+                */

The pathkeys for the EPQ path don't matter.  It'll only be called to
recheck one single row, and there's only one order in which you can
return one row.

-               if (bms_equal(em->em_relids, rel->relids))
+               if (bms_is_subset(em->em_relids, rel->relids))

Why do we need this?

-- 
Robert Haas
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