I guess there is for-pay plugin for Interbase but I don't know what it does.

What is the current version of Jboss you are talking here. Do you mean that JBoss wont cluster entity beans?

> Hello together,
>
> in my last thread I had a problem using entity beans
> in my cluster. The problem was that JBoss doesn't do
> the replication in the current version.
>
> Now I'm looking for a free database that supports my
> scenario: I have a cluster of (finally) 15 hosts.
> Each host has it's own JBoss/Tomcat and database
> instance (MySQL at the moment). Requests coming from
> the web are distributed to one of the hosts by a load
> balancer.
>
> In this scenario I can't use Master/Slave database
> clustering, because only one master would be
> writeable for my entity beans. And because I can't
> configure the beans using another DB for writing than
> for reading I need another solution.
> That's why I need synchronous Master/Master database
> clustering. Synchronous would be ideal because I
> don't have any problems with lost updates or anything
> other.
>
> Because my cluster is an academical one I'll have to
> use a free database system. Oracle would be fine, but
> it is a little bit too expensive :-)
> So what are the alternative solutions?
>
> MySQL: Only supports Master/Slave
> PostgreSQL: Only supports Master/Slave, but
> there are some tools in development, supporting syn.
> Master/Master
> SAPDB: Seems to be a Master/Slave solution,
> too
>
> Do you know a free database that supports synchronous
> Master/Master replication?
> I have found no message in this forum saying: I use
> XYZ-DB. That's why I think this could be a nice
> discussion (and that's why I have started a new
> thread)!
>
> Cheers,
> Markus

It depends what you mean by "clustering entity beans".

JBoss will not cluster the *state* of the entity beans: the state is managed by the database, not by JBoss. It is exactly the same for Weblogic, Websphere, etc.

It is a DB-thing, not an AS-thing.

Cheers,


sacha

We are working on such a thing in the Cache/JBoss project. However, we don't replicate at the database level, but instead put a replicated cache in front of the EJB-CMP interceptor. This way, all requests will be replicated in-memory first, then persisted into the database. With a shared-DB scenario, only 1 node writes to the DB, whereas with local DBs every nodes writes to the DB.

If you want DB-replication, I implemented asynchronous replication for HSQLDB (HyperSonic) half a year ago. You may want to look at that code. It should not be too difficult to switch to a synchronous replication scheme (it's actually on my todo list). Note that this is not for production systems (but I think it would be ideal for research).

Bela

The thing is that I modified HSQLDB code, because they didn't have the hooks I needed to get replication going.

So if I wanted synchronous replication I would have to go back, get the latest HSQLDB and apply those changes again.

I therefore decided I'd rather wait until they provide the hooks (this is work in progress) and then I can simply plug in my replication module *without changes to HSQLDB core code*.

So, for now it is up to the HSQLDB team - you may want to follow up with them on their SourceForge fora.
Cheers,

Bela