Rainer,
<VENDOR>
Sybase EAServer has licensed IBM's Encina tx manager in source code form
which acts as our XA/XOpen OTS tx manager. Access to the Tx manager is
available via JTA. The Encina engine therefore runs in-process and does
indeed use logging. Since EAS is written in C we dont have the performance
issues you mention in relation to logging.
</VENDOR>
How do you rollback without tx logging? Like for a hueristic rollback?
Dave Wolf
Internet Applications Division
p.s. Kinda funny we use IBM's engine and IBM doesnt?
> -----Original Message-----
> From: A mailing list for Enterprise JavaBeans development
> [mailto:[EMAIL PROTECTED]]On Behalf Of Rainer Kerth
> Sent: Wednesday, September 13, 2000 4:15 PM
> To: [EMAIL PROTECTED]
> Subject: Re: EJB and the two phase commit
>
>
> Dave Wolf wrote:
> > >
> > > > Very few application servers today can act as 2PC transaction
> > > > managers. The
> > > > only ones I am aware of are <VENDOR> Sybase EAServer </VENDOR>
> > > as well as
> > > > iPlanet 6 and <BLECK>MTS</BLECK>.
> > >
> > > any idea about Websphere Advanced Edition 3.5?
> >
> > Nope. Last time I checked they didnt, except maybe to DB2. Very
> confusing
> > data sheet.
>
> See below for an answer to the question on WebSphere Advanced
> 3.5. Before I
> get to the answer I'd like to
> make two general comments:
>
> Claims for generic support for 2PC w/o specifying the data source and a
> driver do appear to be a little
> vague to me. E.g. when testing JTA support for WebSphere, we found that a
> leading db vendor's JDBC
> driver does not implement the XAResource's forget() and recover() methods.
> So, we can't claim support
> for 2PC to this database, and this is what we try to put into the data
> sheet. Unfortunately, this kind of detail
> sometimes causes our data sheets to be difficult to read. I can assure you
> that we would very much
> prefer simpler statements but our experience is that we actually need to
> prereq a very specific version for
> many products, sometimes even specific fixpack levels, to make
> things work.
> This applies to IBM products
> as well as to other vendor's products.
>
> The other general comment that I have is that support for the JTA
> interfaces is only half of the story and
> is sometimes misinterpreted as full, enterprise level support for 2PC.
>
> Details of this statement are as follows: some vendors do implement JTA
> interfaces but only do a 1PC
> under the covers. They don't claim 2PC support but do this only for J2EE
> compliance. The next level up
> is to implement an external transaction manager in the app server in order
> to drive XA messages through
> the XAResources but without performing transaction logging in this
> transaction manager. This is 2PC as
> long as the app server doesn't crash. If it does crash, the external
> transaction manager looses its state
> and a transaction that is currently committing would hang or time out with
> a heuristic outcome. The enterprise
> level 2PC implementation requires XA messages to drive the two phases of
> the commit process *and*
> transaction logging in the external transaction manager. This allows a
> recovery protocol to be driven in
> the case of an app server failure and to recover the resources even if the
> app server fails. As an
> optimization, if only one resource is involved in a transaction,
> logging in
> the external transaction manager
> can be omitted because commit processing can be reduced to a single phase.
>
> Transaction logging can have a significant performance impact and is
> difficult to implement efficiently in
> Java. This is due to arbitrary GC pauses of the JVM and to the fact Java
> does not allow low level access
> to disks. Current C++ implementations use a low level file I/O APIs for
> transaction logging that actually take
> into account things like disk rotation speed to improve the logging
> performance. This is essential because
> transaction logging can make or break the overall performance of a system.
> Of course, if someone was
> clever enough to configure OS swap files and transaction manager log files
> to reside on the same physical
> disk then there is not much you can do in your code to avoid a performance
> hit.
>
> Now, to answer the question above:
>
> <VENDOR>
> WebSphere Advanced 3.5 supports 2PC *w/o* transaction logging to DB2 and
> Sybase. Oracle JTA
> does not currently work due to problems with the Oracle thin JDBC driver.
> WebSphere Enterprise 3.5 supports 2PC *with* transaction logging across
> Oracle, Informix, DB2, CICS,
> IMS and MQSeries.
> The various product versions required for this functionality are
> documented
> in the software prereqs,
> available from
>
> http://www.ibm.com/software/webservers/appserv/doc/v35/idx_aas.htm
> </VENDOR>
>
> I wonder if the products previously mentioned in this thread implement an
> external transaction manager
> (which I would assume) and if they support transaction logging in the
> external transaction manager?
>
> Regards
>
> Rainer
>
> ------------------------------------------------------------------
> ----------------------------
>
> Rainer Kerth, IBM WebSphere Architecture, [EMAIL PROTECTED]
>
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