Re: Question: update and transaction isolation

Tom Lane wrote:
>
> Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> > Tom Lane writes:

> To my mind, full SERIALIZABLE mode is the only approach that can be
> explained in terms of simple notions like "you see only the data that
> existed at time T".

There's another way. If the current value is different from
that at time T, we may be able to reset the time when the
statement begun, which is equivalent to replaceing the snapshot
(this isn't allowed in serializable mode). Of cource it would
be very difficult to implement(at least effectively).

As I've already mentioned many times SELECT and SELECT ..
FOR UPDATE are alike in appearance but quite different in
nature. For example, the meaning of the snapshot isn't the
same as you've pointed out already in this thread.
It's meaingless for SELECT and UPDATE(SELECT .. FOR UPDATE)
to have a common snapshot.

regards,
Hiroshi Inoue