"J. Matthew Pryor" wrote:
>
> >> Also, how can the EJB container achieve this? Would
> >> this imply that to have entity bean failover all
> >> entity beans would have to be replicated across the
> >> containers? What would be the implication of such
> >> replication on concurrent access to the entity beans?
> >
> >The EJB container achieves that by reloading that entity bean on the
> >other server. It may, or may not, and that might depend on the bean (and
> >certainly the EJB container) replicate the entity bean. If your entity
> >bean simply holds information retrieved from the database, just
> >reloading it on the other server will do the trick.
> >
> >arkin
>
> Surely there is a lot assumed here of the app server and/or database
> replication . I am not aware of how specific app servers might implement CMP
> entity bean replication, but if your failing over because a power spike took
> out the machine on which your database runs, you have to have database level
> replication as well don't you ?
Database replication is up to the database server, it's not in the scope
of EJB. Also UPS is not within the scope of EJB :-)
> How much can realistically be expected of an application server on the CMP
> entity bean replication front if you assume you want to tolerate hardware
> failure of the database server ?
Nothing.
If you are looking for CMP to replicate your database, you are looking
at the wrong place. A replicating RDBMS will be, a) more efficient at
doing the replication, b) not dependent on a particular EJB server, c)
support session beans, non-EJB database access, etc.
Not to tip anyone off, I know Oracle has such an option and I was pretty
impressed with their specs. Buy it instead of buying an EJB server
trying to do the same.
arkin
> Failing over to a new app server instance where the underlying database is
> assumed to still exist doesn't seem that hard, but if you want failover to
> also tolerate loss (or failover) of the underlying database, it seems like
> it would be a lot harder, or at least vendor specific, to me. I'd love to be
> surprised otherwise.
>
> thanks,
> matthew
> | j. matthew pryor <mailto:[EMAIL PROTECTED] >
> | verve, inc. <http://www.verveinc.com/>
>
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--
----------------------------------------------------------------------
Assaf Arkin www.exoffice.com
CTO, Exoffice Technologies, Inc. www.exolab.org
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