Re: Multi-Versions and Vacuum -- cf Oracle & Vacuum alt

I (Mike Mascari) wrote:
>
> Anthony Berglas wrote:
> >
> > A combined response to several posts. I am not advocating Oracle in
> > general, just noting differences and places where Postgres might benefit.
> >
> > ORACLE MVC
> >
> > Oracle definitely has MVC. By default it is in Read Committed mode. But
> > you can still get record locks in both Postgresql and Oracle if you Select
> > FOR UPDATE, which you must do in Read Committed mode to produce correct
> > transactions.
> >
> > ORACLE LOCKING
> >
> > My note about Oracle is that in its Read Committed mode transactions are
> > safer without being Serializable. See http://www.SimpleORM.org/DBNotes.html
> > for details. The difference is subtle but it is is important because
> > otherwise report may not be consistent. And I do not think that there is
> > any down side. So I commend the approach to the Postgres community.
>
> I just tried this in Oracle 8.0.5:

..

>
> Session #1:
> ---------------
> SQL> select * from employees;
>
> 1 Tom
> 3 Jim
>
> So when you say:
>
> "By memory, Oracle has similar behaviour in Read Committed mode except
> that the PostCommitSelect would NOT show the changes made by session
> two, and thus be more serializable."
>
> it doesn't match the behavior with Oracle 8.0.5. Tom and Jim are phantom
> reads, as expected, in Read Committed mode. Perhaps this has changed in
> version 9?

I should have written:

Tom -> non-repeatable read
Jim -> phantom read

but the point remains...

Mike Mascari
mascarm(at)mascari(dot)com