Paul Ramsey <pramsey(at)cleverelephant(dot)ca> writes:
>> Whether I get a parallel aggregate seems entirely determined by the number
>> of rows, not the cost of preparing those rows.
> This is true, as far as I can tell and unfortunate. Feeding tables with
> 100ks of rows, I get parallel plans, feeding 10ks of rows, never do, no
> matter how costly the work going on within. That's true of changing costs
> on the subquery select list, and on the aggregate transfn.
This sounds like it might be the same issue being discussed in
https://www.postgresql.org/message-id/flat/CAMkU=1ycXNipvhWuweUVpKuyu6SpNjF=yHWu4c4US5JgVGxtZQ(at)mail(dot)gmail(dot)com
regards, tom lane