[infinispan-dev] RPCs for non-existant caches ought not throw exception

[Paul Ferraro]

In AS clustering, there are several use cases where a specific cache
instance may not exist (or may not be started) for every member of the
group.  Currently, Infinispan treats this as an exception case, and any
cache operation resulting in an RPC will fail.  This is problematic for
the following AS use cases:

1. For a given clustering service (e.g. web session, SFSBs, entity
caching) there is a shared cache manager for all applications, while
each application uses its own cache instance.  If I have app1 running on
node1 and node2, everything is fine.  But if I deploy app2 on node1,
it's membership will include node2 (because of the shared cache manager)
even though there is no cache instance for app2 on node2.  Consequently,
the cache instances for app2 will be non-functional until app2 is
deployed on node2.
2. In Hibernate's 2nd level cache, custom cache regions are created on
demand.  So, even with a single app running on 2 nodes, the first
request to cache an entity in a custom cache region on node1 will fail,
since the cache corresponding to the region will not exist on node2.

Here's is relevant code in
InboundInvocationHandlerImpl.handle(CacheRpcCommand):

String cacheName = cmd.getCacheName();
ComponentRegistry cr = gcr.getNamedComponentRegistry(cacheName);
long giveupTime = System.currentTimeMillis() + 30000; // arbitraty (?) wait time for caches to start
while (cr == null && System.currentTimeMillis() < giveupTime) {
   Thread.sleep(100);
   cr = gcr.getNamedComponentRegistry(cacheName);
}

if (cr == null) {
   if (log.isDebugEnabled()) log.debug("Cache named {0} does not exist on this cache manager!", cacheName);
   return new ExceptionResponse(new NamedCacheNotFoundException(cacheName));
// return RequestIgnoredResponse.INSTANCE; // Suggested fix?
}

For the perspective of the AS, a request for a non-existent cache should
be treated the same way as a request for a stopped cache (that logic
returns RequestIgnoredResponse.INSTANCE).
As Galder pointed out, handling this case via exception was an explicit
workaround for this issue: https://jira.jboss.org/browse/ISPN-447
In the comments for ISPN-447, Manik seemed to suggest that returning an
exception is merely a workaround until this issue is fixed:
https://jira.jboss.org/browse/ISPN-434

As it stands, this is a blocker issue for AS infinispan integration.

Thoughts?