Date: Tue, 14 Apr 2020 20:14:02 -0700
From: Noah Misch <noah@leadboat.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	masahiko.sawada@2ndquadrant.com, masao.fujii@oss.nttdata.com,
	pgsql-hackers@lists.postgresql.org
Subject: Re: Race condition in SyncRepGetSyncStandbysPriority
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On Tue, Apr 14, 2020 at 04:32:40PM -0400, Tom Lane wrote:
> I wrote:
> > It doesn't seem to me to be that hard to implement the desired
> > semantics for synchronous_standby_names with inconsistent info.
> > In FIRST mode you basically just need to take the N smallest
> > priorities you see in the array, but without assuming there are no
> > duplicates or holes.  It might be a good idea to include ties at the
> > end, that is if you see 1,2,2,4 or 1,3,3,4 and you want 2 sync
> > standbys, include the first three of them in the calculation until
> > the inconsistency is resolved.  In ANY mode I don't see that
> > inconsistent priorities matter at all.
> 
> Concretely, I think we ought to do the attached, or something pretty
> close to it.
> 
> I'm not really happy about breaking ties based on walsnd_index,
> but I see that there are several TAP test cases that fail if we
> do something else.  I'm inclined to think those tests are bogus ...
> but I won't argue to change them right now.

This passes the test battery I wrote in preparation for the 2020-02 thread.