Re: "Transactions are bad, real bad" - discuss

"Paul Vernon" <paul.vernon_at_ukk.ibmm.comm> wrote in message news:b8r8k7$1tj0$1_at_gazette.almaden.ibm.com...
> "Mikito Harakiri" <mikharakiri_at_ywho.com> wrote in message
> news:5NXra.8$i92.264_at_news.oracle.com...
> >
> > "Paul Vernon" <paul.vernon_at_ukk.ibmm.comm> wrote in message
> > news:b8ljgd$383i$3_at_gazette.almaden.ibm.com...
> > > With transactions, this rule is compromised. A user could simply open
a
> > > transaction before the end of the 1 hour deadline, make a bid at then
only
> > > decide to commit (or rollback) the bid at his leisure after the end of
the
> > > deadline.
> >
> > Isn't this problem trivally solved by "flashback" query that auction
> > organizer can run?
> >
> > select max(amount) from bids AS OF "30-APR-2002 12:00"
> >
> > Any transaction not committed before "30-APR-2002 12:00" would have no
> > effect onto the query resultset.
>
> Don't you think that this just highlights why transactions are
troublesome?
>
> AS OF "30-APR-2002 12:00"
> the max bid in the auction closing as 12:00 was $10
>
> AS OF "30-APR-2002 12:15"
> the max bid in the auction closing as 12:00 was $12

I disagree. If auction is closing at 12:00, then organizers issue AS OF "30-APR-2002 12:00"
query and get the exact snapshot of what bids were placed at 12:00. Quering AS OF "30-APR-2002 12:15"
doen't make any sence at all. What is so special about 12:15, as you never listed it in the problem statement?

> Don't we want the timeline that the 'auction closing time' is part of to
be
> the same as the timeline that 'row insertion timestamp' is part of and
both be
> the same as the AS OF timeline?

Row insertion timestamp doesn't matter. The commit time does.

> In the above we have two time lines.
> The AS OF timeline that is corrent and consistent - it only moves
forward
> and at any given time there is one state of the database.
> The CURRENT TIMESTAMP timeline that can lag the AS OF timeline. This
> allows changes to appear 'in the past' - it make time travel possiable.
Not,
> IMO a good model of reality.

I don't understand the concept of 2 timelines (and all this temporal SQL bu..it). I understand, however, the concept of time in special relativity theory, and concurrency models in CS based upon partial time ordering relationship (when there is a causal connection between some space-time events but not all of the events). Sometimes it *might* be possible to embed a "timeline" with partial ordering into a cartesian product of 2 linear timelines. Received on Thu May 01 2003 - 19:37:04 CEST