[jboss-user] [Clustering/JBoss] - Re: strace shows futex

[bstansberry@jboss.com]

I just pinged the JGroups folks again. You can also try the jgroups user mail list at https://lists.sourceforge.net/lists/listinfo/javagroups-users .

Re: HASingletonController, first thing to understand is that who the master is is a function of what nodes in the cluster have that HASingletonController deployed. There is the overall cluster view, which more people are familiar with, and then something that I call the "service view", which reflects what nodes in the cluster have a particular service deployed.

So, say you have a 4 node cluster and the view for the cluster is {A, B, C, D}.  But the "Foo" service's HASingletonController is only deployed on 2 nodes. So it's service view is {C, D}. The "Bar" service's HASingletonController is deployed on a different 2 nodes, so it's service view is {A, B}.

In this example the master for the "Foo" service is C and the master for "Bar" is A.

A service view is always a subset of the overall cluster view.  If a node crashes, it's removed from all service views.

How all this works behind the scenes is an HASingletonController uses a component of the HAPartition known as the DistributedReplicantManager.  The DRM basically maintains the service views.  When for example the "Foo" service HASingletonController is deployed on node D, it registers itself with the DRM by invoking the DRM add method.  DRM in turn invokes a method on the HAPartition which does a group RPC telling the other DRMs in the cluster that "Foo" is now available on D. Those DRMs in turn issue a notification to the "Foo" HASingletonController on their nodes telling them that the service view for the "Foo" service has changed, and now includes "D".  From that they can determine who the master is.

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