On Mon, May 2, 2016 at 2:44 PM, David G. Johnston
<david.g.johns...@gmail.com> wrote:
> Does this apply to the extent that a value of 1 is likely worse than 0 since
> the leader is now tasked with accumulating but there is only one process
> actually working to provide the leader data?

I don't know what that means, but it doesn't work like that.  If the
worker can't generate data fast enough, the leader will also run the
parallel portion of the plan.  So 1 is unlikely to be worse than 0; in
fact it's often a lot better.

> I'm inclined to accept max_parallel_workers where a value of 0 means no
> parallelism and the non-zero counts indicate the number of workers in
> addition to the required leader.

That's how it works now.

> Though that does suggest "additional" as a valid option.  Something like
> "max_additional_workers".  Just how overloaded is the term "worker".  If
> worker is understood to mean "a process which implements execution of [part
> of] a query plan" the word additional leaves no ambiguity as to where the
> leader is accounted for.
> It does significantly reduce grep-ability though :(
> max_additional_parallel_workers...

I don't think that it's likely to be very clear what "additional"
refers to in this context.

Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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