If you’re facing challenges with database availability and scalability, Oracle Real Application Clusters (RAC) may be the solution you need.

This guide cuts through system and landscape complexities to provide a clear understanding of Oracle RAC’s cluster-based technology, ensuring your critical applications remain accessible and efficient, regardless of demand spikes or server disruptions.

Keep reading to learn about the essential concepts, setup guidelines, best practices, and optimization tips for effective Oracle RAC deployment and how our team of Oracle consultants can help.

Key Takeaways

  • Oracle RAC offers high availability by providing clusters of servers access to shared storage, enhancing application performance and reliability, particularly for OLTP applications. It includes features like user session failover, continuous operation during node outages, and dynamic scalability.
  • Key components of Oracle RAC include Oracle Clusterware for managing resources and ensuring high availability, shared storage solutions like OCFS2 and ASM for data consistency and access across nodes, and specialized background processes for data management and inter-instance communication.
  • Managing Oracle RAC environments effectively involves assuring compatibility before installation, meticulous planning and using administrative tools for design and deployment, and ongoing performance monitoring and evaluation with tools like Oracle Enterprise Manager, AWR, and ASH reports.

The Power of Oracle RAC

Illustration of clustered servers in Oracle RAC environment

Oracle RAC is not just a database; it’s a powerhouse designed to ensure the continuity of operations and prevent a single point of failure. Oracle RAC operates across a cluster of servers, all having access to shared storage, providing high availability, scalability, and fault tolerance.

For Online Transaction Processing (OLTP) applications, Oracle RAC’s capabilities greatly enhance overall application performance and reliability. The unique architecture of Oracle RAC means that it offers a range of benefits that are hard to match with a single instance Oracle database compared to a traditional Oracle instance.

High Availability

Oracle RAC’s high availability is one of its notable strengths. It enhances the database system’s availability by removing the possibility of individual database servers becoming single points of failure. Oracle RAC One Node, a single-instance database option, further eliminates the database server as a single point of failure.

The high availability framework of Oracle RAC ensures that database components are always maintained in a running state to support continuous service availability. Its unique capabilities allow:

  • User sessions to failover and safely replay changes during outages
  • A database to continue operating even during an outage of one or more compute nodes within the cluster
  • Users connected to the failed nodes are reconnected to surviving nodes


Beyond high availability, Oracle RAC offers advanced scalability. This capability enables databases to:

  • Scale dynamically without impacting operations or necessitating alterations to application code
  • Make it easier to manage database growth while maintaining system stability
  • Allow businesses to easily scale out or scale in as necessary with minimal downtime

The scalable architecture of Oracle RAC includes the facility to add compute nodes to an existing cluster and to expand the shared storage space according to demand. This flexibility in scaling makes Oracle RAC a highly adaptable solution that can effectively handle fluctuating workload demands.

Load Balancing

The power of Oracle RAC is also demonstrated by its load-balancing capabilities. Oracle RAC uses services to align sessions with the appropriate instances, enabling precise load balancing. In the event of a service disruption, Oracle RAC’s intelligent cluster reconfiguration automatically redirects connections to the remaining instances, balancing the workload and mitigating their impact.

Runtime Connection Load Balancing dynamically distributes connections across the pool based on the current performance metric of each database instance, optimizing resource use. The Single Client Access Name (SCAN) feature in Oracle RAC offers a stable entry point for client connections, greatly simplifying client configuration and supporting load balancing performance.

Key Components of Oracle RAC

Illustration of Oracle Clusterware architecture

Oracle RAC is not a monolithic entity but comprises several key components that work together to ensure efficient operation. These core components include Oracle Clusterware, shared storage solutions, and background processes. Understanding how these components interact and contribute to the functionality of Oracle RAC is crucial for effectively managing an Oracle RAC environment.

Oracle Clusterware

Oracle RAC heavily relies on Oracle Clusterware as a vital component of its Oracle software suite, offering a high availability and resource management framework for all applications on supported platforms. As a portable cluster software, Oracle Clusterware clusters independent servers to operate as a cohesive system, a critical capability for effective RAC environments.

Oracle Clusterware manages the following resources, which are fundamental to maintaining high availability in Oracle RAC:

  • VIP addresses
  • Databases
  • Listeners
  • Services

It also employs Fast Application Notification (FAN) to quickly inform applications of changes in the cluster configuration and service level statuses. Oracle Clusterware’s ability to manage third-party resources and agents ensures high availability and smooth operation for various applications and processes on the cluster.

Shared Storage Solutions

Illustration of shared storage solutions in Oracle RAC

Oracle RAC also significantly depends on shared storage solutions, such as similar database files. These solutions allow multi-node access to data files, enabling high availability and scalability. The Oracle Cluster File System (OCFS2) is purpose-built for Oracle RAC environments, offering a shared disk file system that supports simultaneous file access across different nodes. Additionally, the ASM cluster file system is another solution that can be utilized in such environments.

Oracle RAC can also leverage the Network File System (NFS) for data and recovery file storage on Network-Attached Storage (NAS) systems, with the Direct NFS Client optimizing file serving and storage capabilities. These shared storage solutions ensure that all servers in the database cluster can access the necessary data, providing a solid foundation for Oracle RAC’s high availability and scalability.

Background Processes

Oracle RAC databases combine the memory structures and background processes of two or more instances to manage and process data. Using Cache Fusion, Oracle RAC environments logically combine each instance’s buffer cache to ensure data consistency and coherence across the cluster.

Background processes are vital in inter-instance communication, resource monitoring, and global resource management. Managing the number of Global Cache Service Processes is crucial for ensuring sufficient capacity and optimal performance on nodes, especially when consolidating multiple databases into a single cluster.

Navigating Oracle RAC Implementation Processes

Implementing Oracle RAC involves several steps, including meeting compatibility requirements, installing the software, creating a database, and extending the grid infrastructure. Each step is critical for a successful Oracle RAC implementation and requires careful planning and execution.

Compatibility Requirements

Compatibility assurance is a prerequisite before installing Oracle RAC. To ensure compatibility, you need to:

  1. Install Oracle Clusterware software infrastructure
  2. Set up a communications protocol for interprocess communication
  3. Ensure that all servers in the database cluster can access shared storage configured for higher availability and performance.

A private, dedicated network connection is recommended for Oracle RAC, along with a network designed to have no single points of failure, including implementing a virtual IP. The AL32UTF8 character set is recommended to configure Oracle RAC database instances for global deployments. Meeting these compatibility requirements ensures a smooth and successful Oracle RAC implementation.

Installation and Database Creation

Following the satisfaction of compatibility requirements, the subsequent step is the installation of Oracle RAC. Oracle Clusterware must first be installed on all nodes in the cluster, with installation steps differing based on the operating system. Once Oracle Clusterware is set up, Oracle RAC software is established through the Oracle Universal Installer (OUI) and can be done silently using response files.

After installing the Oracle RAC software, an Oracle RAC database is created using the Database Configuration Assistant (DBCA) to configure database options, services, and storage using the ASM disk group. This installation and database creation process sets up the necessary software and structures for the Oracle RAC to operate as a reliable database service.

Extending Grid Infrastructure

To extend the grid infrastructure in Oracle RAC, new nodes must have access to the shared storage used by existing nodes and fulfill identical network and storage specifications. Preparing new nodes for joining the Oracle RAC cluster includes selecting the RAC for extension and confirming that working directories are set up on the new nodes. By doing so, the Oracle grid will be efficiently expanded.

Oracle RAC Database is then installed on the new nodes and configured to align with the existing Oracle RAC setup. After adding a node to the cluster, the Oracle RAC database is extended to incorporate the new node by creating an instance through the Database Configuration Assistant, ensuring it’s properly integrated with the Clusterware. This process of developing the grid infrastructure allows Oracle RAC to scale and adapt to increasing workload demands.

Managing Oracle RAC Environments

Ensuring optimal performance and high availability of Oracle RAC environments depends on effective management and involves design and deployment strategies, administrative tools, and ongoing monitoring and performance evaluation. Effective management of Oracle RAC environments helps ensure they continue to deliver the high availability, scalability, and performance they are designed to provide.

Design and Deployment

The first step in designing and implementing a high availability strategy with Oracle RAC involves thoroughly analyzing the business drivers. This analysis is crucial for understanding the specific needs and requirements of the organization. This involves:

  • Defining service level requirements
  • Planning for capacity
  • Ensuring performance objectives are consistently met, even during unplanned outages or scheduled maintenance events.

High availability in Oracle RAC deployments demands meticulous planning to avoid single points of failure within the database and the entire system infrastructure. Adopting best practices and establishing operational procedures with proper support contracts is critical for successful Oracle RAC deployment. Oracle’s recommendations for Oracle RAC include separating Oracle Cluster Registry (OCR) and voting disks onto different volume groups and maintaining an odd number of voting disks to maintain robustness against failures.

Administrative Tools

Utilizing multiple administrative tools is essential for effectively managing Oracle RAC environments. Oracle Enterprise Manager is recommended for administering Oracle RAC, as it simplifies complex tasks such as configuring backups, performing recovery, and managing database instances. Oracle Enterprise Manager Cloud Control offers a one-click extension feature to add new nodes to an existing Oracle RAC cluster quickly and easily.

The Cluster Verification Utility (CVU) and ORAchk and Exachk tools are recommended for regular checks to validate Oracle RAC cluster components and ensure best practice compliance. For Oracle Exadata Real Application Clusters, Exachk provides a comprehensive examination of system health, covering software and configuration best practices and issuing critical alerts for components like:

  • Storage
  • Network
  • Clusterware
  • ASM
  • Database

Monitoring and Performance Evaluation

Keeping a close eye on the system and evaluating performance is fundamental to managing Oracle RAC environments. Oracle RAC utilizes the following tools to facilitate performance evaluation and tuning:

  • Global dynamic performance views
  • Automatic Workload Repository
  • Active Session History reports
  • Oracle Enterprise Manager’s Cluster Database Performance page

Oracle RAC leverages performance views as essential sources of real-time performance information across all instances. Monitoring specific Oracle RAC wait events and statistics, like Global Cache Service metrics, helps evaluate inter-instance performance concerns. Performance tuning involves:

  • Using SQL Tuning Advisor
  • Utilizing the query optimizer
  • Considering host hardware configurations to resolve bottlenecks
  • Utilizing tools like Automatic Shared Memory Management
  • Adjusting initialization parameters such as FAST_START_MTTR_TARGET

Advanced Oracle RAC Features

Oracle RAC also offers many advanced features besides its basic functionalities, adding to its versatility and power. These include Oracle RAC One Node, Automatic Workload Management, and Oracle Multitenant and Database In-Memory integration. Understanding and leveraging these features can help organizations optimize their Oracle RAC environments for high availability, scalability, and performance.

Oracle RAC One Node

Oracle RAC One Node brings the robustness of RAC to single-instance databases, providing a reliable single-database solution. It is designed to run a single instance of a database on a shared disk system, a design choice similar to Oracle RAC. This solution facilitates any Oracle Database workload and allows for a seamless upgrade to a total multi-instance Oracle RAC without requiring changes to existing applications.

Oracle RAC One Node enables:

  • Rolling patches
  • Relocation of database services without incurring system downtime
  • Database consolidation and virtualization, letting administrators configure multiple single-instance databases on a single physical server or virtualized environment, effectively managing multiple servers.

Automatic Workload Management

Oracle Automatic Workload Management (AWM) plays a key role in evenly distributing workloads across databases in an Oracle RAC to ensure optimal performance and high availability. Workloads can be flexibly managed by grouping them to optimal instances within the Oracle RAC through services, bolstering overall system performance and utilization.

Runtime Connection Load Balancing ensures intelligent distribution of connections and consistent service levels by dynamically adjusting to the current performance provided by database instances. The Load Balancing Advisory in Oracle RAC provides recommendations on where to direct application requests based on real-time analysis of the service metrics and adherence to defined service policies.

Fast Connection Failover allows for rapid re-establishment of database connections following instance failures, thereby minimizing downtime and enhancing the robustness of the RAC environment.

Oracle Multitenant and Database In-Memory

Oracle RAC can be integrated with Oracle Multitenant, allowing a single container database to host multiple pluggable databases, enhancing data isolation and maintaining efficiency. The integration of Oracle RAC with Oracle Multitenant ensures high availability and scalability for each pluggable database, as they can be distributed across multiple nodes of the RAC cluster.

Oracle RAC supports hosting pluggable databases within a multitenant container database and supporting non-container databases. This integration brings the benefits of Oracle RAC, including high availability, scalability, and load balancing, to the flexible, efficient model of pluggable databases.

Wrapping Things Up

Oracle Real Application Clusters (Oracle RAC) is a powerful solution designed to provide high availability, scalability, and load balancing for databases. By utilizing key components such as Oracle Clusterware, shared storage solutions, and background processes, Oracle RAC ensures robust and efficient operation.

Implementing Oracle RAC involves meeting compatibility requirements, installing the software, creating a database, and extending the grid infrastructure. Effective management of Oracle RAC environments is crucial and involves design and deployment strategies, use of administrative tools, and ongoing monitoring and performance evaluation.

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Frequently Asked Questions

What is Oracle RAC used for?

Oracle RAC is used for high availability, scalability, fault tolerance, load balancing, failover, and horizontal scalability by allowing a single Oracle database to run across multiple servers, accessing shared storage. It is ideal for creating scalable environments for mission-critical business applications.

What is the difference between Oracle and Oracle RAC?

The main difference between Oracle and Oracle RAC is that a single instance database has a one-to-one relationship, while Oracle RAC allows multiple computers to run Oracle RDBMS software simultaneously to access a single database, providing clustering.

What does RAC stand for in Oracle?

RAC stands for Real Application Clusters, a high-availability solution for Oracle databases, allowing multiple database instances to support an application simultaneously.

What is the difference between Oracle RAC and Oracle Clusterware?

The main difference between Oracle RAC and a cluster is that a cluster can comprise interconnected computers or servers, whereas Oracle RAC enables multiple instances of the same database to run on different servers in a cluster, improving reliability and performance.

How is the architecture of the Oracle RAC database configured?

Oracle RAC database architecture allows multiple instances to access a single database running on multiple nodes. It uses Oracle Clusterware to bind multiple servers into a single system, enabling clustered Oracle databases.