RAC

The Cluster Ready Services (CRS) process, which is the main clusterware process that manages all other clusterware processes and resources, and provides the communication infrastructure for the cluster.

The Cluster Synchronization Services (CSS) process, which manages the distributed lock manager and ensures that data is synchronized and consistent across all nodes in the cluster.

The Global Enqueue Service (GES) process, which manages the allocation and management of enqueues, which are used to coordinate access to shared resources in the cluster.

The Oracle Cluster Registry (OCR) process, which maintains the cluster configuration and membership information, and stores it in a central repository that is accessed by all nodes in the cluster.

The Voting Disk process, which is used to maintain quorum and ensure that the cluster can continue to operate even if some nodes become unavailable.

RAC patching is a process of updating the software that runs an Oracle Real Application Clusters (RAC) database. The high-level steps for patching a RAC database are as follows:

Download and unzip the patch files from the Oracle website.

Stop the RAC database and all related services.

Apply the patch to each node in the RAC cluster.

Start the RAC database and verify that it is functioning properly.

Run any post-patch scripts or steps that are provided with the patch.

These steps may vary slightly depending on the specific patch being applied and the version of the RAC database. It is important to carefully follow the instructions provided with the patch to ensure that the patch is applied correctly and the RAC database continues to function properly.