CHAPTER 11
Tuning RAC and Using Parallel Features

Oracle's Parallel Server was first introduced in Oracle 6.1 (beta) and Oracle 6.2 (limited customer release production) but widely used only on VAX/VMS. Not until Oracle 9i did Oracle truly have a clustering product (Real Application Clustering—RAC) when they rewrote the code for the product almost completely (95 percent, I am told). In Oracle 10g, RAC has not only has matured but has become the cornerstone for grid computing (entire grids of servers using the Oracle RAC or clustering architecture).

In addition to using many servers to help increase availability and improve performance, Oracle also has improved the parallel query technology that was first introduced with Oracle release 7.1. The Parallel Query Option (PQO), which is now called the Parallel Executions Option (PEO), makes query operations and DML statements parallel, generating potentially significant performance benefits. Enhancements have been added to the PEO for each release of the RDBMS kernel. In Oracle 10g, most operations can be parallelized, including queries (Parallel SQL Execution), DML, DDL operations, intra-partition parallelism, parallelism for data replication and recovery, and data loading; multiple parallel query server processes can even execute against the same partition.