Re: ALTER TABLE transaction isolation problem

Kevin Grittner-5 wrote
>> [ Examples shows that both SERIALIZABLE and REPEATABLE READ
>> transactions could see an empty table which was not empty as of
>> the point the snapshot was taken.  For that matter, it was not
>> empty at any later point, either. ]
>
> Why don't we rewrite tuples with their existing xid in such cases?
> The current state of affairs seem to me to be a pretty clear bug.

In the ADD COLUMN scenario this results in the new column being visible when
it technically should not be but that is not likely a huge concern.

In the DROP COLUMN scenario you can no longer see data which should
technically be present.  I guess if you go to use that data and it is not
present you'd get an error which is the technically correct response anyway
so probably not a huge concern either.

The idea of altering a record but not updating its xid sounds unclean but
I'm not able to evaluate any potential pitfalls of such an action.

David J.




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