On 5 August 2015 at 01:54, Tom Lane <t...@sss.pgh.pa.us> wrote: > David Rowley <david.row...@2ndquadrant.com> writes: > > During working on allowing the planner to perform GROUP BY before joining > > I've noticed that cost_agg() completely ignores input_startup_cost > > when aggstrategy == AGG_HASHED. > > Isn't your proposed patch double-counting the input startup cost? > input_total_cost already includes that charge. The calculation > reflects the fact that we have to read all of the input before we > can deliver any aggregated results, so the time to get the first > input row isn't really interesting. > > If this were wrong, the PLAIN costing path would also be wrong, but > I don't think that either one is. > > Sorry, false alarm, you're right.
This was a bug in my code where I was adding disable_cost to the startup_cost, but not to the total_cost. -- David Rowley http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Development, 24x7 Support, Training & Services
