What is the difference between Parallel Query and Parallel Server?
Parallel Query allows one to break a SELECT or DML statements into multiple smaller chunks and have PQ slaves execute those smaller chunks on separate CPU’s in a single box. Oracle Real Application Clusters (RAC) allows one to take advantage of a multi-node clustered environment for availability and performance reasons. It is commonly used to access a very large database from different nodes of a cluster. More information about Oracle RAC can be obtained from the RAC FAQ. If both RAC and OPQ are available one can split operations across multiple CPUs and multiple nodes in a cluster for even further performance improvements.
