On Tue, 2008-09-02 at 12:28 -0400, Tom Lane wrote:
> Simon Riggs <[EMAIL PROTECTED]> writes:
> > As discussed on 26 June, "Join Removal/Vertical Partitioning", here's a
> > patch to remove joins in certain circumstances.
> Some points not made in the thread so far:

Various comments accepted and agreed.

> > +                    * XXX Seems not worth searching partial indexes 
> > because those
> > +                    * are only usable with a appropriate restriction, so 
> > the
> > +                    * only way they could ever be usable is if there was a
> > +                    * restriction that exactly matched the index predicate,
> > +                    * which is possible but generally unlikely.
> I haven't thought this through entirely, but wouldn't a partial index be
> okay if it's marked predOK?  You might be right that the case is
> unlikely, but if it's only one extra line to support it ...

As of now, its it is predOK then that implies there was a qual on the
checkrel so can't remove the join. So no need to check.

> > +   if (removable && 
> > +           joinrel->cheapest_total_path < keeprel->cheapest_total_path)
> This test on cheapest_total_path seems pretty wacko 

and stuff below it definitely is, from upthread discussion.

Hang fire on more comments - its a short patch but needs a few thwacks
from the cluestick yet before next review.

 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support

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