Parallel Clause and Small Tables

If you have multiple CPUs available you may come up with the idea to set parallel execution on every table. The Oracle Optimizer should decide about the degree of parallelism or even if is necessary to use parallel execution at all. What's a great thing on big tables shows up badly on small ones. The split up of all the work over more than one CPU may result in an overhead which exceeds the execution time needed by one CPU by factors. While the Optimizer recognises for index accesses not to use parallel execution it doesn't for full table scans. This sounds reasonable at first hand but consider that often full table scans are the fastest option on smaller tables.

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