"Marko Kreen" <markokr@gmail.com> writes:
> IMHO the core operations are already as stable as PostgreSQL use
> of MVCC, as the module just exports backend internal state...
Well, it exports backend internal state that did not exist before 8.2
(ie, XID epoch). So it doesn't seem all that set in stone to me.
> Another thing can can be done is more compact representation for
> txid_snapshot type, but that also won't affect core operation.
That's another thing that's likely to become very much harder to change
once it's in core. People keep threatening to produce a working
in-place-upgrade process, and once that's reality the on-disk
representation of core types is going to be hard to change.
regards, tom lane