Re: max_parallel_degree context level

On 12 February 2016 at 04:55, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, Feb 11, 2016 at 10:32 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
>> Is it slower if you request N workers, yet only 1 is available?
>
> I sure hope so.  There may be some cases where more workers are slower
> than fewer workers, but those cases are defects that we should try to
> fix.

It would only take anything but the CPU to be a bottleneck for this to
be highly likely the case.
If a non-parallel query is bound on I/O, then adding workers is most
likely going to slow it down further. I've seen this when testing
parallel aggregates.

-- David Rowley                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services