What is parallel query optimization?

Parallel query optimization is the process of analyzing a query and choosing the best combination of parallel and serial access methods to yield the fastest response time for the query. Parallel query optimization is an extension of the serial optimization strategies discussed in earlier chapters. In addition to the costing performed for serial query optimization, parallel optimization analyzes the cost of parallel access methods for each combination of join orders, join types, and indexes. The optimizer can choose any combination of serial and parallel access methods to create the fastest query plan.