I will explain What is GRD in Oracle RAC in this post.
What is GRD in Oracle RAC
Single Instance and Oracle RAC Instances have the same processes and memory structures. In addition to Single Instance, Oracle RAC has some more additional process and memory structures like Global Cache Service ( GCS ), Global Enqueue Service ( GES ) processes and the global resource directory (GRD) collaborate to enable cache fusion.
If you want to learn more details about Oracle RAC Architecture, read the following post.
GRD ( Global Resource Directory )
Oracle Cluster operations require synchronization among all instances to control shared access to resources. Real Application Clusters ( RAC ) uses the GRD ( Global Resource Directory ) to record information about how resources are used within a cluster instances.
The processes that manage local resource coordination in a cluster database are identical to the local resource coordination processes in single instance Oracle. This means that row and block level access, space management, system change number (SCN) creation, and data dictionary cache and library cache management are the same in Real Application Clusters as in single instance Oracle. Global resource coordination, however, is somewhat more complex as described later in this chapter.
Global Resource Directory includes the following types of shared resource information as follows.
- Data block identifiers, such as a data block addresses
- Locations of the most current versions of data blocks if they have been read into buffer caches on multiple nodes in the cluster
- The modes in which data blocks are being held by instances: (N) Null, (S) Shared, or (X) Exclusive
- The roles in which data blocks are being held by each instance: local or global
- Buffer caches on multiple nodes in the cluster
If you want to learn more details about Oracle RAC Installation, read the following post.
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