Bruce Momjian wrote:
>
> > > The ratio in a well tuned system should well favor outdated tuples.
> > > If someone ever adds "dirty read" it is also not the case that it
> > > is guaranteed, that nobody accesses the tuple you currently want
> > > to undo. So I really miss to see the big difference.
> >
> > It will not be guaranteed anyway as soon as we start removing
> > tuples without exclusive access to relation.
> >
> > And, I cannot say that I would implement UNDO because of
> > 1. (cleanup) OR 2. (savepoints) OR 4. (pg_log management)
> > but because of ALL of 1., 2., 4.
>
> OK, I understand your reasoning here, but I want to make a comment.
>
> Looking at the previous features you added, like subqueries, MVCC, or
> WAL, these were major features that greatly enhanced the system's
> capabilities.
>
> Now, looking at UNDO, I just don't see it in the same league as those
> other additions.
Hmm hasn't it been an agreement ? I know UNDO was planned
for 7.0 and I've never heard objections about it until
recently. People also have referred to an overwriting smgr
easily. Please tell me how to introduce an overwriting smgr
without UNDO.
regards,
Hiroshi Inoue