Re: serializable isolation level behavior question

On Oct 21, 10:36 am, "Bob Jones" <e..._at_me.not> wrote:
> "Martin T." <bilbothebagginsb..._at_freenet.de> wrote in messagenews:1161426546.350950.93250_at_m7g2000cwm.googlegroups.com...
>
>
> > DA Morgan wrote:
> >> Bob Jones wrote:
> >> > "Martin T." <bilbothebagginsb..._at_freenet.de> wrote in message
> >> >news:1161326760.938515.185890_at_m73g2000cwd.googlegroups.com...
> >> >> DA Morgan wrote:
> >> >>> joeNOS..._at_BEA.com wrote:
> >> (snipped)
>
> >> > For the last time, if you want this to work, either use delete or table
> >> > lock. Serializable does not affect DDLs.
>
> >> > Don't complain to the manufacturer if your SUV cannot run on water.
>
> >> I have to confess I too am shaking my head in amazement.
>
> >> Hopefully not betraying my ignorance but my understanding is the same as
> >> yours. I can't understand why anyone would use DDL and expect it to
> >> behave transactionally.
> >> --
>
> > As others in this thread have said, and what you and Bob seem to
> > continue to ignore is: The transaction that started as serializable did
> > not issue any DDL. In fact it only issues select statements, it's not
> > even trying to change anything. So:Yes, it was the other party issued a DDL. That's why the serializable does
> not work because, I repeat, DDLs do not write to rollback.
>
> > * Is Oracle giving us a useful answer when we delete: Yes - The
> > serialization works.
> > * Is Oracle giving us a useful answer when we drop: Yes - we get an
> > error.
> > * Is using truncate on a table where anyone else works on bad design:
> > Yes!
> > * Is Oracle giving us a useful answer when we query the truncated
> > table: No, it violates the serialization instead of raising an error.
>
> > What's the point of serialization if you can't rely on it to produce a)
> > the right answer or b) an error.
>
>Isolation levels are not one-sided affairs, and only apply when all parties
> are transactional. "Serializable" does not mean no one else can do anything
> to the table during your transaction, it just decides what your transaction
> reads in the next operation.

Isolation means just that, isolation. It is designed and intended as protection from others. The spec for serializable includes the next lower isolation level, which is repeatable read. Yes, it doesn't mean someone else can't do something to a table. It doesn't mean someone else can't take a sledge hammer to the disk. As you say, Serializable defines what your tx reads next. It says that the DBMS will either ensure your repeated read gets the same data or ensure that your transation cannot commit.
Joe Received on Sat Oct 21 2006 - 14:28:00 CDT