[infinispan-dev] HotRod, ClientIntelligence and client-side key location

[Manik Surtani]

I've been thinking about how we handle this, and I think we have a problem with smart clients where clients have the ability to locate the key on the server cluster in order to direct the request to the specific node.

The problem is in hash code calculation.  The HotRod protocol caters for this with regards to calculating node address hash code by passing this in the topology map (see "Hasher Client Topology Change Header" in [1]), but the only way this can be meaningfully used is if the client has the ability to calculate the hash code of the key in the same manner the servers do.  Firstly, this is hard when consumed by non-Java clients as you'd need to implement the way the JDK calculates the hash code of a byte array.  Second, you'd need detailed and specific knowledge of any bit spreading that takes place within Infinispan - and this is internal implementation detail which may change from release to release.

So the way I see it I can't see how non-Java clients will be able to locate keys and then direct requests to the necessary nodes.  In fact, even with Java clients the only way this could be done would be to send back marshalled Addresses in the topology map, *and* have the same version of the Infinispan server libs installed on the client, *and* ensure that the same JDK/JVM version is used on the client.  

Can we think of a better way to do this?  If not, is it worth still supporting client-side consistent hash based key location for the weird but vaguely workable scenario for Java-based clients?

Thoughts?

Cheers
Manik


[1] http://community.jboss.org/wiki/HotRodProtocol
--
Manik Surtani
manik at jboss.org
Lead, Infinispan
Lead, JBoss Cache
http://www.infinispan.org
http://www.jbosscache.org