On Tue, May 31, 2016 at 10:23 AM, Josh berkus <j...@agliodbs.com> wrote:
> It's still WAY simpler to understand "max_parallel is the number of
> parallel workers I requested".

(Sorry Josh, somehow hit reply, not reply-all)

Yes, it is. But as long as parallel workers are not really that
distinct to the leader-as-worker when executing a parallel query, then
you have another consideration. Which is that you need to care about
how many cores your query uses first and foremost, and not the number
of parallel workers used. I don't think that having only one worker
will cause too much confusion, because users will trust that we won't
allow something that simply makes no sense to happen.

In my parallel create index patch, the leader participates as a worker
to scan and sort runs. It's identical to a worker, practically
speaking, at least until time comes to merge those runs. Similarly,
parallel aggregate does not really have much for the leader process to
do other than act as a worker.

Peter Geoghegan

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