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Oracle Parallel Processing by Sanjay Mishra, Tushar Mahapatra

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Integrated Distributed Lock Manager

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.

Integrated Distributed Lock Manager

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 ...

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