Proposal: Select ... AS OF Savepoint

Hi,
I would like to propose an additional feature for Postgres to enable
time-travelling inside a transaction.

I went through the source code and i found Savepoint is already saving the
necessary information. But currently it doesn't store the CommandId.

This change, if implemented would save the command id into savepoint state,
increase the command id counter for every savepoint and finally we can issue
a command like
(One more global variable to store the current state)
Select ... as of savepoint savepoint-name.

This would reduce the requirement for Serializable transactions in some
cases and adds one more feature under the umbrella of postgres.

--
Thanks,
Gokul.
CertoSQL Project,
Allied Solution Groups.
(www.alliedgroups.com)