Re: Why is Postgres only using 8 cores for partitioned count? [Parallel Append]

On Tue, 16 Feb 2021 at 02:12, Fabio Pardi <f.pardi@portavita.eu> wrote:
>
> On 14/02/2021 22:16, Gavin Flower wrote:
> > While I agree it might be good to be able specify the number of workers, sure it would be possible to derive a
suitabledefault based on the number of effective processors available?
 
>
> I had the same problem and my conclusion was that it is not possible to go above 8 cores because of Amdahl's law on
parallelcomputing. More here: https://en.wikipedia.org/wiki/Amdahl%27s_law
 

That would really depend on what the non-parallel part of the equation
was.  There are some plan shapes such as GROUP BY or aggregate queries
with very few or just 1 group where the serial portion of the
execution is very small indeed.

David