Alvaro Herrera <alvherre@commandprompt.com> wrote:
> As for sanity -- I regard multixacts as a way to store extended
> Xmax information. The original idea was obviously much more
> limited in that the extended info was just locking info. We've
> extended it but I don't think it's such a stretch.
Since the limitation on what can be stored in xmax was the killer
for Florian's attempt to support SELECT FOR UPDATE in a form which
was arguably more useful (and certainly more convenient for those
converting from other database products), I'm wondering whether
anyone has determined whether this new scheme would allow Florian's
work to be successfully completed. The issues seem very similar.
If this approach also provides a basis for the other work, I think
it helps bolster the argument that this is a good design; if not, I
think it suggests that maybe it should be made more general or
extensible in some way. Once this has to be supported by pg_upgrade
it will be harder to change the format, if that is needed for some
other feature.
-Kevin