Re: Support Parallel Query Execution in Executor

Simon Riggs <simon(at)2ndquadrant(dot)com> writes:

> I think it would be useful to think about exactly what type of
> query/activity we are looking to improve the performance on. That way we
> can understand the benefit of this proposal and take some baseline
> measurements to analyse what is happening for those cases.

I find the focus on sequential scans, index scans, etc. quite odd when you're
discussing parallel query processing. The whole goal of parallel query
processing is to bring more *cpu* to bear on the problem. That's going to be
most relevant when you're cpu bound, not i/o bound.

The queries I would expect to be helped most by parallel query processing are
queries that involve sorting. For example, a big merge join with two sorts on
either side could perform the two sorts simultaneously. If they provide the
results of the final pass to a third thread it can execute the merge join and
the rest of the query plan while the sorts are still executing on two other
processors.

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greg