Using Weblogic and EJB 1.1 along with TOPLink as your container then (i) is
optional. Although you buy a number of other limitiations with it.
- Doug
-----Original Message-----
From: A mailing list for Enterprise JavaBeans development
[mailto:[EMAIL PROTECTED]]On Behalf Of Jonathan K. Weedon
Sent: Tuesday, July 10, 2001 10:19 AM
To: [EMAIL PROTECTED]
Subject: Re: Serializable isolation level (RE: [EJB-INT] To scale or to
be correct: that is the question)
"Zetie, Carl" wrote:
> Now I have a question for the list (if anybody is still reading!) When
> people write that VendorX app server CMP "implements" serializable
isolation
> by default, do they mean (i) that the CMP is actually checking for update
> conflicts, (ii) that the CMP is verifying that the database is
implementing
> serializable isolation for this transaction, or (iii) that the CMP
/assumes/
> that the database is serializing the tx and therefore is actually doing
/no/
> verification itself.
Carl,
Yes, when Evan said that Sybase implements serializable isolation by
default,
he meant (i) "that the CMP [engine] is actually checking for update
conflicts".
In Borland AppServer, this is not the default behavior (which Krishnan
complained about) but is an optional behavior. In WebLogic, this is not a
supported behavior (at least not with EJB 1.1, although Cedric amusingly
suggested that customers can rewrite their applications using EJB 2.0 if
they
need this functionality in WebLogic.) In WebLogic, case (iii) holds: "the
CMP [engine] /assumes/ that the database is serializing the tx and therefore
is actually doing /no/ verification itself."
I am not aware of a product that does (ii). I would argue that (ii) is a
currently
a burden on the deployer when using (iii). That is, if the CMP engine is
assuming
that the database is doing the serialization, then it is up to the deployer
to ensure
that the database is configured appropriately.
Which is an interesting point unto itself. I am willing to bet that a very
large
percentage of EJB applications are not configured correctly with respect to
serialization (that is, the default serialization is used from the appserver
and
from the database). If you are using anything other than Sybase's
appserver,
you will therefore be subject to "stomping" updates, using this default
configuration. Which motivates Krishnan's suggestion that appserver-based
verification be the default behavior, since we can't reasonably convince
Oracle to make serializable be the default transaction isolation (due to the
performance overhead).
-jkw
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