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What is Oracle RAC?
Oracle Real Application Clusters, commonly known as Oracle RAC, is a database clustering technology developed by Oracle Corporation. It allows multiple database instances to operate on different servers, sharing a single physical database. This enables the database to provide high scalability, availability, and performance for mission-critical systems.
Basic Concepts of Oracle RAC
Oracle RAC consists of a cluster database, where the database is spread across multiple servers, and Oracle Clusterware, which is the underlying software that enables the cluster functionality. The key concepts of Oracle RAC include:
1. Cluster Database: A cluster database is a single logical database that spans multiple physical servers. It allows concurrent access and shared data among multiple instances.
2. Instances: An instance refers to the Oracle database software and memory structures needed to access the database. Each server in the cluster runs one or more database instances.
3. Cache Fusion: Cache Fusion is a shared memory architecture in Oracle RAC that allows instances to directly access and share data blocks in the system global area (SGA) of other instances. It minimizes disk I/O and enhances performance.
4. Global Cache Service (GCS): GCS manages the global resources, including data blocks and cache buffers, ensuring data consistency among all instances in the cluster. It handles cache fusion and global coordination.
5. Oracle Clusterware: Oracle Clusterware provides the necessary infrastructure to manage Oracle RAC environments. It manages the cluster resources, monitors the health of cluster components, and facilitates high availability operations.
High Availability in Oracle RAC
Oracle RAC offers high availability by providing several features and mechanisms:
1. Automatic Failover: In case of a server or instance failure, Oracle RAC automatically redirects the affected workload to another available server. This ensures continuous access to the database without any downtime or interruption.
2. Load Balancing: Oracle RAC distributes the workload evenly across all instances in the cluster, utilizing the available server resources effectively. This prevents any single server from becoming overloaded and helps in optimizing performance.
3. Transparent Application Continuity: Oracle RAC seamlessly handles planned and unplanned outages by preserving the session state and rerouting the application connection to another available instance. It ensures uninterrupted user experience, even during database changes or failures.
4. Rolling Upgrades: Oracle RAC allows upgrading the database and clusterware version, one node at a time, without bringing down the entire system. This minimizes downtime and enables continuous operations during the upgrade process.
5. Data Guard Integration: Oracle RAC can be integrated with Oracle Data Guard to provide disaster recovery and data protection. This combination ensures data synchronization and failover capabilities, enhancing overall system availability.
In conclusion, Oracle RAC is a robust and high-performing technology that enables the seamless integration of multiple servers to provide scalability, availability, and performance for enterprise-level database systems. It ensures continuous access to data, load balancing, and automatic failover, making it an ideal choice for organizations with critical database requirements.
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