Re: Rename max_parallel_degree?

Peter Geoghegan <pg@heroku.com>

From: Peter Geoghegan <pg@heroku.com>

To: Josh berkus <josh@agliodbs.com>

Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, Noah Misch <noah@leadboat.com>, David Rowley <david.rowley@2ndquadrant.com>, Amit Kapila <amit.kapila16@gmail.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, Magnus Hagander <magnus@hagander.net>, Bruce Momjian <bruce@momjian.us>, PostgreSQL-development <pgsql-hackers@postgresql.org>

Date: 2016-05-31T18:27:14Z

Lists: pgsql-hackers

On Tue, May 31, 2016 at 11:22 AM, Josh berkus <josh@agliodbs.com> wrote:
>> I think we can hope that developers are going to be less confused about
>> that than users.
>
> Makes sense.

Maybe EXPLAIN doesn't have to use the term parallel worker at all. It
can instead use a slightly broader terminology, possibly including the
term "core".

> One more consistency question: what's the effect of running out of
> max_parallel_workers?
>
> That is, say max_parallel_workers is set to 10, and 8 are already
> allocated.  If I ask for max_parallel_X = 4, how many cores to I use?

Well, it depends on the planner, of course. But when constrained only
by the availability of worker processes, then your example could use 3
cores -- the 2 remaining parallel workers, plus the leader itself.

> Presumably the leader isn't counted towards max_parallel_workers?

Exactly.

-- 
Peter Geoghegan