Adam Brusselback <adambrusselback(at)gmail(dot)com> writes:
> As suggested in the Postgres slack channel by lukasfittl, I disabled
> hashagg on my old server, and ran the query again. That changed one piece
> to a groupagg (like was used on the new server) and the performance was
> similar to the 9.6.1 box.
If the problem is "new server won't use hashagg", I'd wonder whether
the work_mem setting is the same, or whether maybe you need to bump
it up some (the planner's estimate of how big the hashtable would be
might have changed a bit).
regards, tom lane