Re: [HACKERS] Parallel tuplesort (for parallel B-Tree index creation)

On Thu, Jan 18, 2018 at 1:14 PM, Peter Geoghegan <pg@bowt.ie> wrote:
> That seems pretty far fetched.

I don't think it is, and there are plenty of other examples.  All you
need is a query plan that involves significant CPU work both below the
Gather node and above the Gather node.  It's not difficult to find
plans like that; there are TPC-H queries that generate plans like
that.

> But even if it wasn't, my position
> would not change. This could happen only because the planner
> determined that it was the cheapest plan when
> parallel_leader_participation happened to be off. But clearly a
> "degenerate parallel CREATE INDEX" will never be faster than a serial
> CREATE INDEX, and there is a simple way to always avoid one. So why
> not do so?

That's an excellent argument for making parallel CREATE INDEX ignore
parallel_leader_participation entirely.

-- 
Robert Haas
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