> > It should also be noted that an ALTER TABLE / SET TYPE implemented with
> > the above idea with run into the 2x diskspace issue as well as take
> > quite a while to process.
>
> I think that if the 'SET TYPE' operation is ever to be rollback-able, it
> will need to use 2x diskspace. If it's overwritten in place, there's no
> chance of fallback... I think that a DBA would choose to use the command
> knowing full well what it requires? Better than not offering them the
> choice at all!
True, but if we did the multi-version thing in pg_attribute we may be
able to coerce to the right type on the way out making it a high speed
change.