Locks and Deadlocks
by Riyaj Shamsudeen
Oracle database uses a locking scheme as a coordination mechanism to protect critical resources from concurrent changes. In a single-instance database, instance-level locks are sufficient as the locks need to be visible in the local instance only, so local locks are sufficient. In a RAC database, resources must be globally visible and so a new layer—Global Enqueue Services (GES)—is employed to implement a global locking scheme.
Global Resource Directory (GRD) is a memory area designed to keep track of the state of resources in a RAC database. GRD is distributed across all active instances of ...