Re: SSI atomic commit

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
> Kevin and Dan also pointed out that a 2PC transaction can stay in 
> prepared state for a long time, and we could optimize that by setting 
> prepareSeqNo only at the final COMMIT PREPARED. I objected to that, for 
> the reason that it's currently very convenient for testing purposes that 
> a transaction prepared with PREPARE TRANSACTION is in the exact same 
> state as regular transaction that's going through regular commit processing.

Seems to me there's a more fundamental reason not to do that, which is
that once you've done PREPARE it is no longer legitimate to decide to
roll back the transaction to get out of a "dangerous" structure --- ie,
you have to target one of the other xacts involved instead.  Shouldn't
the assignment of a prepareSeqNo correspond to the point where the xact
is no longer a target for SSI rollback?
        regards, tom lane