Oracle RAC Background process

 Oracle RAC Background process

In Oracle Real Application Clusters (RAC), background processes play a crucial role in managing the shared resources, coordination, and synchronization among the multiple instances that make up the cluster. These processes are specific to RAC and work together to ensure high availability, scalability, and fault tolerance. Here are some important background processes in Oracle RAC:

1. Global Cache Service (GCS) Process: The GCS process manages the Global Cache Service, which is responsible for coordinating access to data blocks residing in the global cache across different instances. It handles block requests, grants or denies access, and manages the distributed lock management for data concurrency.

2. Global Enqueue Service (GES) Process: The GES process manages the Global Enqueue Service, which handles lock management for non-data resources such as shared resources, library cache objects, and sequences across the RAC instances. It manages and coordinates the access and release of these enqueues across multiple instances.

3. Global Resource Directory (GRD) Process: The GRD process maintains the Global Resource Directory, which is a shared memory structure that contains information about the ownership and location of cached data blocks and enqueues. It provides a centralized view of the resources and their statuses across the RAC instances.

4. Cache Fusion Process: The Cache Fusion process handles the inter-instance communication and transfer of data blocks between the instances' local caches. It enables efficient data sharing and avoids unnecessary disk I/O by allowing instances to access each other's data blocks directly.

5. Network Listener Process: The Network Listener process listens for incoming connection requests from clients and routes them to the appropriate RAC instance. It handles the initial connection establishment and enables clients to connect to any available instance in the RAC cluster.

6. LMS Process: The Lock Manager Server (LMS) process handles lock management and coordination between instances. It manages the distributed locks and ensures data consistency and integrity in the RAC environment.

7. GES/GCS Recovery Server (RS) Process: The GES/GCS Recovery Server process handles recovery operations in case of instance failures. It manages the recovery and redistribution of cached data blocks and enqueues to ensure data availability and consistency.

8. LMON Process: The Global Enqueue Service Monitor (LMON) process monitors the health and availability of the GES and GCS processes. It detects failures and takes appropriate actions to recover or reconfigure the resources in case of failures or reconfiguration events.

These are some of the key background processes in Oracle RAC. They work together to provide high availability, scalability, and efficient resource management in a clustered database environment.