| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | David Rowley <dgrowleyml(at)gmail(dot)com> |
| Cc: | Jeevan Chalke <jeevan(dot)chalke(at)enterprisedb(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Marti Raudsepp <marti(at)juffo(dot)org>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Allowing NOT IN to use ANTI joins |
| Date: | 2014-07-14 14:50:59 |
| Message-ID: | 15078.1405349459@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> On Mon, Jul 14, 2014 at 3:00 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Ugh. I'm back to being discouraged about the usefulness of the
>> optimization.
> Are you worried about the planning overhead of the not null checks, or is
> it more that you think there's a much smaller chance of a real world
> situation that the optimisation will succeed?
Both. We need to look at how much it costs the planner to run these
checks, and think about how many real queries it will help for. The
first is quantifiable, the second probably not so much :-( but we still
need to ask the question.
regards, tom lane
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