On 03/27/2017 05:51 PM, Robert Haas wrote:
On Mon, Mar 27, 2017 at 9:54 AM, Tom Lane <t...@sss.pgh.pa.us> wrote:
Robert Haas <robertmh...@gmail.com> writes:
On Mon, Mar 27, 2017 at 1:29 AM, Rushabh Lathia
<rushabh.lat...@gmail.com> wrote:
But it seems a bit futile to produce the parallel plan in the first place,
because with max_parallel_workers=0 we can't possibly get any parallel
workers ever. I wonder why compute_parallel_worker() only looks at
max_parallel_workers_per_gather, i.e. why shouldn't it do:
parallel_workers = Min(parallel_workers, max_parallel_workers);
Perhaps this was discussed and is actually intentional, though.
It was intentional. See the last paragraph of
https://www.postgresql.org/message-id/ca%2btgmoamsn6a1780vutfsarcu0lcr%3dco2yi4vluo-jqbn4y...@mail.gmail.com
Since this has now come up twice, I suggest adding a comment there
that explains why we're intentionally ignoring max_parallel_workers.
Hey, imagine if the comments explained the logic behind the code!
Good idea. How about the attached?
Certainly an improvement. But perhaps we should also mention this at
compute_parallel_worker, i.e. that not looking at max_parallel_workers
is intentional.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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