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Hi Craig,
I was hoping that JServ would support sharing of session objects between
JServ instances. I believe that the next version of the Servlet API (2.1)
supports a ServletContext mechanism for sharing objects between servlets.
It is feasible that this could be coded to support the kind of functionality
we are after.
We are looking at JavaSpaces at the moment, the problem with a JavaSpace
however is that it is still a single point of failure (as with a database),
an application running on a single machine. Admittedly you can configure a
JavaSpace so that the objects are persistent and therefore a crash in the
JavaSpace would be more of an inconvenience than a disaster. I did read a
good article that claimed JavaSpaces would become really useful when
multiple JVMs would hose a single JavaSpace with some complex algorithms to
keep synchronisation.
KC
-----Original Message-----
From: Craig R. McClanahan
[mailto:[EMAIL PROTECTED]]
Sent: Wednesday, September 22, 1999 1:08 AM
To: Java Apache Users
Subject: Re: Sharing objects between JServ instances?
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KC Wolff-Ingham wrote:
> -----------------------------
> Please read the FAQ!
> <http://java.apache.org/faq/>
> -----------------------------
>
> Is it possible to share Java objects between Jserv
instances? I'm
> particularly interested in the clustered scenario where
multiple Jservs
> across a number of machines are sharing the load. The
problem with this
> being that if a Jserv goes down you lose any objects that
was being stored
> by that JVM. I've thought about using a database machine
to store the data,
> but this again funnels into a single point of failure.#
>
The generic version of this question becomes "is it possible
to share objects
between Java virtual machines?" The core class libraries
give you some ways
to send objects back and forth (RMI, CORBA) but there's no
automated
persistence or replication layer that exists in the standard
APIs for Apache
JServ (or any other Java app) to rely on.
However, this has been an area of active research. I would
suggest looking in
to some of the following topics:
* ObjectSpace Voyager (http://www.objectspace.com) supports
the
ability for objects to migrate from one JVM to another.
* IBM has support for a somewhat similar mechanism in their
"aglets"
concept, at the Alphaworks web site (don't remember the
URL offhand).
* JavaSpaces (http://java.sun.com) is an experimental
technology from
Sun that sounds like it addresses this concern directly.
Given a layer on top of which to build, it would be feasible
to add this kind
of support into the way that Apache JServ 1.0 currently does
load balancing.
But that's going to take some pretty intricate work.
Volunteers?
>
> Thoughts anyone?
>
> KC Wolff
>
Craig McClanahan
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