FAQ

On 6/7/13 2:23 PM, Tom Lane wrote:
As for other databases, I suspect that ones that have parallel execution
are probably doing it with a thread model not a process model.
Oracle 9i was multi-process, not multi-threaded. IIRC it actually had dedicated IO processes too; backends didn't do their own IO.

We certainly need to protect the use case of queries that run in milliseconds, and clearly parallelism won't help there at all. But we can't ignore the other end of the spectrum; you'd need a LOT of communication overhead to swamp the benefits of parallel execution on a multi-minute, CPU-bound query (or in many cases even IO bound).
--
Jim C. Nasby, Data Architect jim@nasby.net
512.569.9461 (cell) http://jim.nasby.net

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