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Re: [COMMITTERS] pgsql: Temporarily (I hope) disable flattening of IN/EXISTS sublinks

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: [COMMITTERS] pgsql: Temporarily (I hope) disable flattening of IN/EXISTS sublinks
Date: 2009-03-28 17:01:41
Message-ID: 18903.1238259701@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers
Bruce Momjian <bruce(at)momjian(dot)us> writes:
> Tom, you mentioned this should be a TODO item.  Do we put it on our main
> TODO, and if so, in what section?

Optimizer/executor I guess.  It's a pretty vague TODO though.  We need
some way to consider alternative join orders for joins that do not
semantically commute.  When I wrote that CVS log entry I was thinking
in terms of fixing the executor so that the joins actually could
commute, which would involve some way of separating the
force-vars-to-null behavior of an outer join from the actual execution
of the join.  I don't know how practical that really is though (and
also I've got a feeling it likely would fall foul of some patent or
other).  Or maybe it could be solved entirely in the planner, but I
don't have an idea of what the planner's internal representation would
have to look like to do that.

			regards, tom lane

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