Re: BUG #15882: Select .... UNION ALL

From: David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>
To: "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>
Cc: "v(dot)campanella47(at)gmail(dot)com" <v(dot)campanella47(at)gmail(dot)com>, "pgsql-bugs(at)lists(dot)postgresql(dot)org" <pgsql-bugs(at)lists(dot)postgresql(dot)org>
Subject: Re: BUG #15882: Select .... UNION ALL
Date: 2019-07-02 12:55:35
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On Tue, 2 Jul 2019 at 21:22, David G. Johnston
<david(dot)g(dot)johnston(at)gmail(dot)com> wrote:
> It occurs to me you are likely benefitting from the new parallel query infrastructure here.

Yeah, most likely.

It can be disabled globally by changing enable_parallel_append = off
in postgresql.conf. However, relying on the query outputting rows in
some order without an ORDER BY clause is asking for trouble. It looks
as though there are only 13 rows to sort, so I don't think an ORDER BY
will cost much.

David Rowley
PostgreSQL Development, 24x7 Support, Training & Services

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