Database resources such as data blocks, index blocks, rollback segments, and the data dictionary are shared among all OPS instances. To prevent conflicts, a locking mechanism is needed to control access to these resources. The Integrated Distributed Lock Manager (IDLM) provides this locking mechanism and does the following:
Maintains a list of shared database resources
Allocates locks on these resources
Coordinates lock requests
Keeps track of granted locks on resources
Two background processes, the Lock Manager Daemon (LMD) and the Lock Monitor (LMON), together with a distributed lock area in the SGA, constitute the Integrated Distributed Lock Manager. These components are shown in Figure 6.5.
Figure 6-5. Integrated Distributed Lock Manager
The locking status of various database resources is maintained in an area of the SGA referred to as the distributed lock area . This lock information is distributed across all OPS nodes. Each node maintains locking status for a subset of database resources. The node that maintains information on a particular database resource is called the master node for the particular resource. Lock requests by any node for a resource are referred to the master node for that resource. Distributing lock information across many nodes provides fault tolerance. If one node fails, only a subset of the lock information needs to be redistributed ...