Re: Client server distributed caching

[Thomas Mahler]

Hi again,

Martin J. Wells wrote:

Thanks for the reply Thomas.

Correct. Cache synchronization (by means of PB.invalidate(oid)) between multiple OJB caches is only implemented

for C/S mode.

C/S mode means: The PersistenceBroker client (in your case the SessionBean) is running in a different JVM than the PB server.
C/S mode is useful only if you want to scale the OJB backend. In your case you have already scaled the frontent (that is multiple EJB containers running your SessionBeans).

Actually, the app doesn't currently run EJB, just JSP/Java talking
direct SQL, the frontends/sessions are loadbalanced,

OK.

but the backend/SQL
isn't. It's currently hitting the DB for everything (don't come back as
an SQL server in another life, trust me).

In my application's case, objects are typically bound to an

app-server

session, with a large number of updates occurring local to the

session.

However, there are exceptions where another app-server may do an

update

on such an object. In this case I (obviously) need to remotely

invalidate

the object. I'm trying to avoid having my app-servers (12 or so) all

have

to go across the network to get object data. We're talking
about a *very* high event rate (~300-500 per sec), where the vast
majority are on local session objects.

I agree. Using C/S mode in your case is IMO not an option. C/S mode is

much slower (factor 10 - 100) than running OJB in singlevm mode.

But faster in my case than going to the DB for everything. But the key
is local caching, with distributed synchronization.

I recommend to implement a manual invalidation scheme. This is not that difficult, as OJB provides all you need.

1.You'll need a special InvaldationSessionBean providing a method invalidate(Identity oid). (You could also use the PersistenceBrokerServer SessionBean implementation for this)

2. You'll have to maintain a list of all your appservers in the cluster

Do you mean develop an RMI layer/protocol that communicates this between
servers? Or is there something in OJB that facilitates this already
(don't really mind).

You could use RMI, EJB SessionBeans, Servlet or a SocketServer to do this.
OJB provides Server implementations for SocketServer, Servlet, SessionBean. So in your case I'd suggest to use the servlet based impl to avoid to implement an RMI server.

3. Once a server updates an Object belonging to another server you perform a remote call on 1.) to invalidate the objects.

Regards,
Marty


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