| From: | Josh berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Peter Geoghegan <pg(at)heroku(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, Bruce Momjian <bruce(at)momjian(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Logic behind parallel default? WAS: Rename max_parallel_degree? |
| Date: | 2016-05-31 18:05:51 |
| Message-ID: | 574DD27F.4060409@agliodbs.com |
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| Lists: | pgsql-hackers |
On 05/31/2016 11:00 AM, Tom Lane wrote:
> ! If this occurs, the plan will run with fewer workers than expected,
> ! which may be inefficient. The default value is 2. Setting this
> ! value to 0 disables parallel query execution.
Is there a thread on how we determined this default of 2? I can't find
one under likely search terms.
I'm concerned about the effect of overallocating parallel workers on
systems which are already running out of cores (e.g. AWS instances), and
run with default settings. Possibly max_parallel_workers takes care of
this, which is why I want to understand the logic here.
--
--
Josh Berkus
Red Hat OSAS
(any opinions are my own)
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