To: Michal Taborsky <michal.taborsky@mall.cz>
Cc: pgsql-performance@postgresql.org
Subject: Re: Searching union views not using indices 
In-reply-to: <436B848F.5030402@mall.cz> 
References: <436B4836.7030300@mall.cz> <13815.1131118294@sss.pgh.pa.us>
	<436B848F.5030402@mall.cz>
Comments: In-reply-to Michal Taborsky <michal.taborsky@mall.cz>
	message dated "Fri, 04 Nov 2005 16:55:59 +0100"
Date: Fri, 04 Nov 2005 12:53:07 -0500
Message-ID: <15833.1131126787@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Michal Taborsky <michal.taborsky@mall.cz> writes:
> OK. Mystery (sort of) solved. After you told me it works for you I had 
> to assume the problem was somewhere else. And, indeed, it was, though 
> it's not too obvious.

> The two attributes are actually not of tybe bigint, but of type 
> "crm_object_id", which is created as follows:

> CREATE DOMAIN "public"."crm_object_id" AS
>    bigint NULL;

Ah.  The problem is that the UNION's output column is bigint, and the
type discrepancy (bigint above, domain below) discourages the planner
from pushing down the WHERE condition.

There's a related complaint here:
http://archives.postgresql.org/pgsql-bugs/2005-10/msg00227.php

If we were to change things so that the result of the UNION were still
the domain, not plain bigint, then your example would be optimized the
way you want.  I'm unsure about what other side-effects that would have
though.

			regards, tom lane