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

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)postgresql(dot)org>
Cc: pgsql-committers(at)postgresql(dot)org
Subject: Re: pgsql: Temporarily (I hope) disable flattening of IN/EXISTS sublinks
Date: 2009-03-28 02:07:26
Message-ID: 200903280207.n2S27QN13789@momjian.us (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers
Tom, you mentioned this should be a TODO item.  Do we put it on our main
TODO, and if so, in what section?

---------------------------------------------------------------------------

Tom Lane wrote:
> Log Message:
> -----------
> Temporarily (I hope) disable flattening of IN/EXISTS sublinks that are within
> the ON clause of an outer join.  Doing so is semantically correct but results
> in de-optimizing queries that were structured to take advantage of the sublink
> style of execution, as seen in recent complaint from Kevin Grittner.  Since
> the user can get the other behavior by reorganizing his query, having the
> flattening happen automatically is just a convenience, and that doesn't
> justify breaking existing applications.  Eventually it would be nice to
> re-enable this, but that seems to require a significantly different approach
> to outer joins in the executor.
> 
> Modified Files:
> --------------
>     pgsql/src/backend/optimizer/prep:
>         prepjointree.c (r1.63 -> r1.64)
>         (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/prep/prepjointree.c?r1=1.63&r2=1.64)
> 
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-- 
  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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