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

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(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 19:28:33
Message-ID: 200903281928.n2SJSXB15081@momjian.us (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers
Tom Lane wrote:
> 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.

Yea, this is beyond the detail we normally put in the TODO list.  If we
want to add this I am afraid we will need to document other optimizer
items as well.

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

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