Re: Race condition in SyncRepGetSyncStandbysPriority

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.