From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Vik Fearing <vik(dot)fearing(at)dalibo(dot)com> |
Cc: | David Rowley <dgrowley(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Thomas Mayer <thomas(dot)mayer(at)student(dot)kit(dot)edu> |
Subject: | Re: Window function optimisation, allow pushdowns of items matching PARTITION BY clauses |
Date: | 2014-06-27 01:35:11 |
Message-ID: | 4570.1403832911@sss.pgh.pa.us |
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Vik Fearing <vik(dot)fearing(at)dalibo(dot)com> writes:
> On 06/27/2014 02:49 AM, Tom Lane wrote:
>> In exactly the same way, it isn't safe to push down quals into
>> subqueries that use DISTINCT unless the quals are non-volatile. This
>> consideration is missed by the current code, and I think that's a bug.
>> Given the lack of prior complaints, I'm not excited about back-patching a
>> change to prevent pushing down volatile quals in the presence of DISTINCT;
>> but I think we probably ought to fix it in 9.5, and maybe 9.4 too.
> Why wouldn't it go back all the way to 9.0? (assuming 8.4 is dead)
People get unhappy when minor releases de-optimize queries that had
been working for them. It's not too late to change the behavior of
9.4, but I'm hesitant to do it in already-released branches, especially
in the absence of any complaints from the field.
> Are you going to take care of all this, or should David or I take a
> crack at it? The commitfest app still shows Ready for Committer.
I can deal with it.
regards, tom lane
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