From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jeff Janes <jeff.janes@gmail.com>
cc: "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Subject: Re: postgres_fdw and column casting shippability
In-reply-to: 
 <CAMkU=1wuSiR++ujs-O+eAATcOm7MkQGJ1SLBHbDVy7C8TBz8UA@mail.gmail.com>
References: 
 <CAMkU=1wuSiR++ujs-O+eAATcOm7MkQGJ1SLBHbDVy7C8TBz8UA@mail.gmail.com>
Comments: In-reply-to Jeff Janes <jeff.janes@gmail.com>
	message dated "Mon, 15 May 2017 14:42:14 -0700"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <22430.1494886968.1@sss.pgh.pa.us>
Date: Mon, 15 May 2017 18:22:48 -0400
Message-ID: <22431.1494886968@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-performance-owner@postgresql.org

Jeff Janes <jeff.janes@gmail.com> writes:
> I've tried versions 9.6.3 and 10dev, and neither do what I expected.  It
> doesn't seem to be a planning problem where it thinks the fast plan is
> slower, it just doesn't seem to consider the faster plans as being options
> at all.  Is there some setting to make it realize the cast is shippable?

AFAICS, postgres_fdw doesn't have any knowledge of CoerceViaIO parse
nodes, so it's never going to consider this type of brute-force cast
as shippable.  Normal casts would presumably be shippable if the
underlying function is considered safe.

Looks like a round-tuit-shortage issue rather than anything fundamental.

			regards, tom lane


-- 
Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance