A storage control unit detects a change in a configuration of a plurality of logical subsystems included in the storage control unit. The storage control unit sends a notification, wherein the notification indicates the change in the configuration of the plurality of logical subsystems. The storage control unit receives data transfer requests directed at available logical subsystems in the storage control unit, wherein the available logical subsystems are determined based on the configuration of the plurality of logical subsystems.

A dynamic queue allocation and de-allocation mechanism for managing traffic flowing through a switching node. If a packet matches conditions of a particular QoS policy rule, a determination is made as to whether a queue associated with the matched QoS policy rule exists on an egress port that is to forward the packet. If such a queue does not exist, a determination is made as to whether enough resources are available for dynamically creating the queue according to the QoS action parameters of the matched QoS policy rule. If the new queue may not be created because of resource limitation, queues of lower priority existing on the port are reclaimed and their resources reassigned to the new queue.

Transactions are granted concurrent access to a data item through the use of an optimistic concurrency algorithm. Each transaction gets its own instance of the data item, such as in a cache or in an entity bean, such that it is not necessary to lock the data. The instances can come from the data or from other instances. When a transaction updates the data item, the optimistic concurrency algorithm ensures that the other instances are notified that the data item has been changed and that it is necessary to read a new instance, from the database or from an update instance.

A migration framework provides for the automatic migration of services in a cluster. A migratable target list contains a list of servers in the cluster capable of hosting a migratable service. A consensus subsystem can select a host server from the migratable target list. A migration manager can migrate the service from a current host to the host selected by the consensus subsystem, and can activate an instance of the service on the selected host server. The migration manager ensures that only one active instance of the service exists in the cluster. A service stub can serve a user request on servers in the migration target, such as by order of preference, until the user request is served on the server hosting the active instance. A lease manager can assign a lease period to determine how long a server hosts an active instance.

The caching of heterogeneous sets of bean is accomplished using a single cache. The beans can be identified by generating a unique identifier that is a combination of the bean's primary key and a self-reference identifier of the bean manager associated with that bean. The average size of a bean set associated with a bean manager can be specified such that the cache allocates memory for that set based on the average size. A callback interface can also be used to shift knowledge of a bean life cycle back to the bean manager.