Hi,
On 2017-07-26 20:12:56 +1200, Thomas Munro wrote:
> Here is a new version of my parallel-aware hash join patchset.
Yay!
Working on reviewing this. Will send separate emails for individual
patch reviews.
> 2. Simplified costing. There is now just one control knob
> "parallel_synchronization_cost", which I charge for each time the
> participants will wait for each other at a barrier, to be set high
> enough to dissuade the planner from using Parallel Hash for tiny hash
> tables that would be faster in a parallel-oblivious hash join.
> Earlier ideas about modelling the cost of shared memory access didn't
> work out.
Hm. You say, "didn't work out" - could you expand a bit on that? I'm
quite doubtful that justaccounting for barriers will be good enough.
> I'll report on performance separately.
Looking forward to that ;)
Greetings,
Andres Freund
