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Introduction to Real Application Clusters

This chapter introduces cluster database processing and the features of Real Application Clusters. This chapter includes the following topics:

• What Is Real Application Clusters?
• The Benefits of Real Application Clusters

What Is Real Application Clusters?

Real Application Clusters harnesses the processing power of multiple interconnected computers. Real Application Clusters software and a collection of hardware known as a cluster unite the processing power of each component to create a robust computing environment.

Real Application Clusters is a breakthrough cluster software architecture with scalability and high availability features that exceed the capabilities of previous Oracle cluster-enabled software products. Real Application Clusters offers significant advantages for all system types. With the increased functionality of Real Application Clusters, all systems and applications can efficiently exploit clustered environments.

You can use Real Application Clusters to deliver high performance, increased throughput, and high availability. Before deploying Real Application Clusters, however, you should understand Real Application Clusters processing.

In Real Application Clusters environments, all active instances can concurrently execute transactions against a shared database. Real Application Clusters coordinates each instance's access to the shared data to provide data consistency and data integrity.

Harnessing the power of clusters offers obvious advantages. A large task divided into subtasks and distributed among multiple nodes is completed sooner and more efficiently than if you processed the entire task on one node. Cluster processing also provides increased performance for larger workloads and for accommodating rapidly growing user populations.

With Real Application Clusters, you can scale applications to meet increasing data processing demands without changing the application code. As you add resources such as nodes or storage, Real Application Clusters extends the processing powers of these resources beyond the limits of the individual components.

Data warehouse applications that access read-only data are prime candidates for Real Application Clusters. In addition, Real Application Clusters successfully manages Online Transaction Processing (OLTP) systems and hybrid systems which combine the characteristics of both read-write and read-only applications. Real Application Clusters also serves as an important component of robust high availability solutions, tolerating failures with little or no downtime.

The Benefits of Real Application Clusters

This section describes the following benefits of Real Application Clusters:

• Lower Overall Cost of Ownership
• Expanded Scalability
• High Availability
• Transparency
• Buffer Cache Management
• Row Locking
• Recovery Manager, Online Backups, and Archiving

Lower Overall Cost of Ownership

Real Application Clusters lowers the overall cost of ownership more effectively than other cluster database products. This is due in great part to the single-system image afforded by the Real Application Clusters architecture.

The degree of system consolidation that you can achieve with Real Application Clusters enables you to use significantly less software and computing equipment than other cluster database products. Moreover, you can deploy Real Application Clusters for any configuration requiring high availability and scalability. In addition, the comprehensive, easy-to-use manageability tools that interact with Real Application Clusters keep your overall costs low by greatly reducing the administrative overhead throughout the life of your project.

Expanded Scalability

A scalable environment enables you to improve performance and add capacity by adding nodes. On some platforms you can add nodes dynamically while your cluster is running.

The number of nodes that Real Application Clusters can actually support is significantly more nodes than any known implementation. Small systems configured primarily for high availability might only have two nodes. Large configurations, however, might have 32 to 64 nodes.

High Availability

High availability refers to systems with redundant components that provide consistent, uninterrupted service, even during failures. In most high availability configurations, nodes are isolated from each other so that a failure on one node does not affect the entire system.

Transparency

The concept of transparency implies that Real Application Clusters environments are functionally equivalent to single-instance Oracle database configurations. In other words, you do not need to make code changes to deploy applications on Real Application Clusters if your applications ran efficiently on single-instance Oracle configurations.

The Cache Fusion feature, which implies a fusing of the multiple buffer caches in a cluster, simplifies the administration of Real Application Clusters environments. With Real Application Clusters and Cache Fusion, you also do not need to perform capacity planning.

Transparency is also realized by efficient resource use at both the application and system levels. For example, you do not need to perform time-consuming resource configurations by examining data access patterns because Real Application Clusters does this automatically.

Buffer Cache Management

Oracle stores resources, such as data block information, in a buffer cache that resides in memory. Storing this information locally reduces database operations and disk I/O. Because each instance has its own memory, Real Application Clusters coordinates the buffer caches of multiple nodes while minimizing disk I/O. This optimizes performance and expands the effective memory to be nearly equal to the sum of all memory in your cluster database.

To do this, Real Application Clusters uses the Global Cache Service (GCS) to coordinate operations among the multiple buffer caches and to optimize Oracle's high performance features. The Global Enqueue Service (GES) also assists in synchronization by managing intranode communications. The GCS and GES are described in more detail later in Part II of this book.

Row Locking

Oracle row locking and multi-version read consistency provide a high degree of concurrency and throughput. Row locking ensures that transactions that modify different rows in the same data block do not need to wait for each other to commit.

Multiversion Read Consistency

Multiversion read consistency ensures that read operations do not block write operations and that write operations do not block read operations. Multiversion read consistency creates snapshots or read consistent versions of blocks that have been modified by a transaction that has not committed. This approach has two key benefits:

• Read operations do not have to wait for resources because users modifying data do not prevent readers from reading
• A snapshot view of the data is available from a specific point in time

Recovery Manager, Online Backups, and Archiving

Real Application Clusters supports the full functionality of Recovery Manager (RMAN) and Oracle Enterprise Manager. Real Application Clusters also supports all Oracle backup and archiving features that are available in single-instance Oracle databases. This includes both online and offline backups of either an entire database or individual tablespaces.

If you operate Oracle in ARCHIVELOG mode, then when a log file is full Oracle converts it to an archive log file before overwriting the log file with information. In Real Application Clusters, each instance automatically archives its own redo log files, or one or more instances can archive the redo log files for some or all of the instances in the cluster database.

If you operate your database in NOARCHIVELOG mode, then you can only make offline backups. If you cannot afford data loss, then Oracle strongly recommends that you use ARCHIVELOG mode.

The remaining chapters in Part I describe the Real Application Clusters architecture and its scalability features.