Re: Index tuple deduplication limitations in pg13

On Tue, Aug 18, 2020 at 1:31 PM Matthias van de Meent
<matthias(dot)vandemeent(at)cofano(dot)nl> wrote:
> Would this extra ordering not effectively be an extra tiebreaker in
> the ordering, applied before the TID? I do not know the full
> implications of that, but I believe that would not result in the
> limitations that you are mentioning.

You could probably do it that way, but again you end up with a lot of
new complexity. Not to mention overhead that would have to be paid by
everyone. It would require code that supported the old way (even if it
was added to Postgres 13) for pg_upgrade, that would also be hard to
test. And it might defeat certain future optimizations based on heap
TID being the only tiebreaker. Having two types of equality might have
to bleed into the optimizer.

It's a question of engineering trade-offs. I don't think that it's worth it.

--
Peter Geoghegan