@Override
    public void updateSubscription( Node node, NodeSubscription subscription )
    {
        // Subscription change should already be stored in the node.
        log.debug( "Updating node subscription (NOP): {} {}", node.getUniqueIdentifier(), subscription.getID() );
    }
Cache that holds all published items (mapped by node ID).
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/InMemoryPubSubPersistenceProvider.java