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From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <david.rowley@2ndquadrant.com>
Cc: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Cc: Pavel Stehule <pavel.stehule@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: why partition pruning doesn't work?
Date: Thu, 07 Jun 2018 23:22:51 -0400
Message-ID: <21787.1528428171@sss.pgh.pa.us> (raw)
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David Rowley <david.rowley@2ndquadrant.com> writes:
> On 8 June 2018 at 03:43, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Maybe there's something I'm missing here, but I sort of hoped that this
>> patch would nuke all the special-case code for Params in this area.
>> Why is there any need to distinguish them from other stable expressions?

> We need to know which Params exist in the Expr as if there are no
> Params, or only external Params, then we can run-time prune during
> startup of the executor.

This does not refute my question.  Why doesn't the same logic apply
to any stable expression?  That is, ISTM a Param is a special case
of that.

			regards, tom lane




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