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Improving performance, and by this we usually mean query performance, is always a hot item with database administrators and users. One of the best and easiest ways to boost performance is to take advantage of the parallel processing option offered by Oracle Database 10g (Enterprise Edition only).
Using normal (that is, serial) processing, the data involved in a single request (for example, user query) is handled by one database process. Using parallel processing, the request is broken down into multiple units to be worked on by multiple database processes. Each process looks at only a portion of the total data for the request. Serial and parallel processing are illustrated in Figures 9-5 and 9-6, respectively.
Parallel processing can help improve performance in situations where large amounts of data need to be examined or processed, such as scanning large tables, joining large tables, creating large indexes and scanning partitioned indexes. In order to realize the benefits of parallel processing, your database environment should not already be running at, or near, capacity. Parallel processing requires more processing, memory, and I/O resources than serial processing. Before implementing parallel processing, you may need to add hardware resources. Let's forge ahead by looking at the Oracle Database 10g components involved in parallel processing.
Oracle Database 10g's parallel processing components are the parallel execution coordinator and the parallel execution servers. The parallel execution coordinator is responsible for breaking down the request into as many processes as specified by the request. Each process is passed to a parallel execution server for execution during which only a portion of the total data is worked on. The coordinator then assembles the results from each server and presents the complete results to the requester.
FIGURE 9-5. Serial processing
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