Tom Lane schrieb am 27.05.2016 um 15:48:
> Thomas Kellerer <spam_eater@gmx.net> writes:
>> while playing around with the parallel aggregates and seq scan in
>> 9.6beta I noticed that Postgres will stop using parallel plans when
>> cpu_tuple_cost is set to a very small number.
>
> If you don't reduce the parallel-plan cost factors proportionally,
> it's not very surprising that reducing that would tend to bias the
> planner away from using parallel plans. See parallel_setup_cost and
> parallel_tuple_cost.
Ah, thanks. That makes sense.
The low value for cpu_tuple_cost was actually a typo.
Adjusting parallel_tuple_cost does bring back the parallel plan.
Thomas