Re: Straightforward changes for increased SMP scalability

"Simon Riggs" <simon@2ndquadrant.com> writes:
> 2. Increase NUM_BUFFER_PARTITIONS from 16 to 256 (or higher).

Do you have any evidence to back up such a large increase?

This change is not free; at the very least it will break
contrib/pg_buffercache, which wants to lock all the partitions at once.
lwlock.c was designed on the assumption that only a pretty small number
of LWLocks would ever be held concurrently, and it will fall over.
I don't think fixing this would be as simple as increasing
MAX_SIMUL_LWLOCKS, because some of the algorithms are O(N^2).

I'd like to see numbers proving that there is useful incremental gain
from going above 32 or 64 partitions, before we start hacking to make
this work.
        regards, tom lane