Oracle Database - Parallel execution in an RAC environment

Card Puncher Data Processing


RAC provides an excellent architecture to incrementally scale your hardware configuration as you require system resources.

You can use the additional resources to:

  • support additional users (and hence reduce the load on the other servers)
  • and/or use the additional resources to directly improve the performance of the operations running on the database.


The inter-node parallel execution may result in a lot of interconnect traffic, then you must ensure you size the interconnect appropriately.

By default the Oracle database enables inter-node parallel execution (parallel execution of a single statement involving more than one node).

If you use a relatively weak interconnect, relative to the I/O bandwidth from the server to the storage configuration, then you may be better of restricting parallel execution to a single node or to a limited number of nodes.

Inter-node parallel execution will not scale with an undersized interconnect.

As a general rule of thumb, your interconnect must provide the total I/O throughput of all nodes in a cluster (since all nodes can distribute data at the same point in time with the speed data is read from disk).

So, if you have a four node cluster, each node being able to read 1GB/sec from the I/O subsystem, the interconnect must be able to support 4 x 1GB/sec = 4GB/sec to scale linearly for operations involving inter-node parallel execution.

It is not recommended to use inter-node parallel execution unless your interconnect satisfies this requirement (or comes very close).

Use instance_groups and parallel_instance_groups or database services (starting with Oracle Database 11g) to limit inter-node parallel execution. It is recommended to use services beginning with Oracle database 11g. The parameter instance_groups is going to be deprecated and only retained for backwards compatibility reasons.

Documentation / Reference

Discover More
Card Puncher Data Processing
Oracle Database - Oracle Real Application Clusters (RAC)

In database computing, Oracle Real Application Clusters (RAC) — an option for the Oracle Database software produced by Oracle Corporation and introduced in 2001 with Oracle9i — provides software for...
Card Puncher Data Processing
Oracle Database - Parallel execution with Oracle Partitioning (parallel partition-wise join)

There are specific optimizations between SQL parallel execution and Oracle Partitioning that you should bear in mind when you plan to use these functionalities together. For example, two large partitioned...
Oracle Database Sql Parallel Execution Principle
Oracle Database - SQL Parallel Execution

Parallel execution was first introduced in Oracle Version 7.3 in 1996 Oracle will make use of Parallel when a table or a statement is marked as “Parallel”. The concept of parallelism is when many...

Share this page:
Follow us:
Task Runner