All database data and metadata objects can be accessed and cached by any instance in the cluster. As a consequence, these objects are subject to distributed locking and cache coherency enforcement, as are runtime global data structures and variables.
The cluster lock manager (CLM) provides distributed locking services for sharing globally accessible and cacheable objects. The CLM creates and queues locks on behalf of locking requests. It arbitrates locking requests for access rights from any instance to any global object in the shared-disk cluster environment.
Locks can have task, transaction, or instance ownership. Locks managed by the local lock manager have task or transaction ownership. Locks managed by the CLM have instance ownership; they are shared among all processes or transactions on that instance, and are retained until another instance requests a conflicting lock mode.
