| From: | Josh berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, 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: Rename max_parallel_degree? |
| Date: | 2016-05-31 18:22:02 |
| Message-ID: | 574DD64A.9090600@agliodbs.com |
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| Lists: | pgsql-hackers |
On 05/31/2016 11:17 AM, Peter Eisentraut wrote:
> On 5/31/16 2:02 PM, Josh berkus wrote:
>> I get where you're coming from, but I think Haas's query plan output is
>> going to show us the confusion we're going to get. So we need to either
>> change the parameter, the explain output, or brace ourselves for endless
>> repeated questions.
>
> Changing the explain output doesn't sound so bad to me.
>
> The users' problem is that the parameter setting ought to match the
> EXPLAIN output.
>
> The developers' problem is that the EXPLAIN output actually corresponds
> to leader + (N-1) workers internally.
>
> I think we can hope that developers are going to be less confused about
> that than users.
Makes sense.
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?
Presumably the leader isn't counted towards max_parallel_workers?
--
--
Josh Berkus
Red Hat OSAS
(any opinions are my own)
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