From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Jeff Janes <jeff.janes@gmail.com>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: postgres_fdw bug in 9.6
In-reply-to: 
 <CA+TgmoZNpXHBp8yADNS7HST9OJAx4_MoZ5ckbxoFhSYo84nY2w@mail.gmail.com>
References: 
 <CAMkU=1y2G8VOVBHv3iXU2TMAj7-RyBFFW1uhkr5sm9LQ2=X35g@mail.gmail.com>
 <6319.1481219450@sss.pgh.pa.us>
 <CA+TgmoZNpXHBp8yADNS7HST9OJAx4_MoZ5ckbxoFhSYo84nY2w@mail.gmail.com>
Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Thu, 08 Dec 2016 13:04:31 -0500"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <7783.1481221687.1@sss.pgh.pa.us>
Date: Thu, 08 Dec 2016 13:28:07 -0500
Message-ID: <7784.1481221687@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

Robert Haas <robertmhaas@gmail.com> writes:
> Maybe it would help for Jeff to use elog_node_display() to the nodes
> that are causing the problem - e.g. outerpathkeys and innerpathkeys
> and best_path->path_mergeclauses, or just best_path - at the point
> where the error is thrown. That might give us enough information to
> see what's broken.

I'll be astonished if that's sufficient evidence.  We already know that
the problem is that the input path doesn't claim to be sorted in a way
that would match the merge clauses, but that doesn't tell us how such
a path came to be generated (or, if it wasn't intentionally done, where
the data structure got clobbered later).

It's possible that setting a breakpoint at create_mergejoin_path and
capturing stack traces for all calls would yield usable insight.  But
there are likely to be lots of calls if this is an 8-way join query,
and probably only a few are wrong.

I'd much rather have a test case than try to debug this remotely.
Bandwidth too low.

			regards, tom lane


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