From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <pg@bowt.ie>
cc: pgsql-committers <pgsql-committers@lists.postgresql.org>
Subject: Re: pgsql: Make heap TID a tiebreaker nbtree index column.
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Comments: In-reply-to Peter Geoghegan <pg@bowt.ie>
	message dated "Thu, 21 Mar 2019 15:34:22 -0700"
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Date: Fri, 22 Mar 2019 12:32:57 -0400
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Peter Geoghegan <pg@bowt.ie> writes:
> On Wed, Mar 20, 2019 at 8:17 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> Actually, I'm not sure why it would be fine to revert 7d3bf73ac now.
>>> Might the problem actually be the order in which OIDs are originally
>>> assigned, or something like that?

>> No, because then things would have been unstable before, no?

> Perhaps. The cost of being wrong here is trivial anyway. I have
> reverted 7d3bf73ac based on the assumption that it's now unnecessary.

Apparently, that case is indeed unstable, cf

https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=3Dfulmar&dt=3D2019=
-03-22%2016%3A15%3A14

I picked up on that because I've also seen it happen on my own
devel machine today, but just once --- I then tried to reproduce it,
but couldn't in several dozen tries.

I'm fairly baffled as to why the output order would be unstable
given the sort, and even more as to why the instability didn't
emerge before.  Any thoughts?

			regards, tom lane