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Expert Oracle RAC 12c by Kai Yu, Riyaj Shamsudeen, Tariq Farooq, Syed Jaffar Hussain

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CHAPTER 11

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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 ...

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