Re: max_parallel_degree context level

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От Simon Riggs
Тема Re: max_parallel_degree context level
Дата
Msg-id CANP8+jJ8UdBR9=ga680iiW=abgC55O=UW5bDQe49zm02ddNrkA@mail.gmail.com
обсуждение исходный текст
Ответ на max_parallel_degree context level  (Thom Brown <thom@linux.com>)
Ответы Re: max_parallel_degree context level  (Robert Haas <robertmhaas@gmail.com>)
Список pgsql-hackers
Дерево обсуждения
On 11 February 2016 at 12:40, Thom Brown <thom@linux.com> wrote:
Hi all,

As it currently stands, max_parallel_degree is set to a superuser
context, but we probably want to discuss whether we want to keep it
this way prior to releasing 9.6.  Might we want to reduce its level so
that users can adjust it accordingly?  They'd still be limited by
max_worker_processes, so they'd at least be constrained by that
setting.

A few questions and thoughts to help decide...

Does it take into account the parallel degree during planning?
Does it take into account the actual parallel degree during planning?

If you make max_worker_processes USERSET won't everybody just set it to max_worker_processes?

How do you prevent or control that? Is that limited by the user's connection limit?

How does the server behave when less servers are available than max_parallel_degree?

Is it slower if you request N workers, yet only 1 is available?

Does pg_stat_activity show the number of parallel workers active for a controliing process?
Do parallel workers also show in pg_stat_activity at all?
If so, does it show who currently has them?
Does pg_stat_statements record how many workers were available during execution?

Is there a way to prevent execution if too few parallel workers are available?

--
Simon Riggs                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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