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DB2® Universal Database for OS/390® Version 7.1 Certification Guide by Susan Lawson, Richard Yevich

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Query Parallelism

In order to reduce elapsed time for a query, DB2 can provide a query with parallel resources, such as several I/O paths or processors. By taking advantage of these resources, queries can run in a shorter period of time allowing more work to be pushed through the system. Parallelism can help improve the performance of I/O and CPU bound read-only queries. It can help queries that are reading large amounts of data, regardless of the filtration.

There will be some overhead associated with the use of parallelism in terms of CPU. DB2 will scale processor intensive work across all available processors. Parallelism can average less than one percent additional CPU overhead for long running queries and less than ten percent for short ...

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