On 05/31/2016 10:03 AM, Tom Lane wrote:
> Josh berkus <josh@agliodbs.com> writes:
>> I realize there's a lot of water under the bridge here, but I think
>> we're going to get 1000 questions on -general of the type: "I asked for
>> 8 parallel workers, why did I only get 7?". I believe we will regret
>> this change.
>> So, one vote from me to revert.
>
> Well, that gets back to the question of whether average users will
> understand the "degree" terminology. For the record, while I do not
> like the current behavior either, this was not the solution I favored.
> I thought we should rename the GUC and keep it as meaning the number
> of additional worker processes.
I will happily bet anyone a nice dinner in Ottawa that most users will
not understand it.
Compare this:
"max_parallel is the maximum number of parallel workers which will work
on each stage of the query which is parallizable. If you set it to 4,
you get up to 4 workers."
with this:
"max_parallel_degree is the amount of parallelism in the query, with the
understanding that the original parent process counts as 1, which means
that if you set it to 1 you get no parallelism, and if you want 4
parallel workers you need to set it to 5."
Which one of those is going to require more explanations on -general and
-novice? Bets?
Let's not be complicated for the sake of being complicated.
--
--
Josh Berkus
Red Hat OSAS
(any opinions are my own)