On Tue, May 13, 2025 at 4:37 PM Scott Mead <scott@meads.us> wrote:
I'll open by proposing that we prevent the planner from automatically selecting parallel plans by default
That seems a pretty heavy hammer, when we have things like parallel_setup_cost that should be tweaked first.
The recommendation that I give to users is pretty straightforward: "Disable automatic parallel query, enable it for queries where you find substantial savings and can control the rate of execution." I always tell users that if they're using parallel query for anything that should execute in less than 5 minutes, they're probably pushing on the wrong tuning strategy as the load induced by the parallel query infrastructure is likely going to negate the savings that they're getting.
Five minutes?! That's not been my experience. Not claiming parallelism is perfect yet, but there are plenty of parallel performance savings under the five minute mark.
