Re: scalability bottlenecks with (many) partitions (and more)

Hi,

On 2025-03-04 14:05:22 +0100, Tomas Vondra wrote:
> On 3/3/25 21:52, Andres Freund wrote:
> >> It's not a proper constant, of course, but it seemed close
> >> enough. Yes, it might confuse people into thinking it's a constant, or
> >> is there some additional impact?
> >
> > That seems plenty. I just looked at the shem sizing function and was confused
> > because I didn't see where the max_locks_per_transaction affects the
> > allocation size.
> >
>
> But the shmem sizing doesn't use FP_LOCK_SLOTS_PER_BACKEND at all, both
> proc.c and postinit.c use the "full" formula, not the macro

Not sure what I brainfarted there...

> >> The one fix I can think of is making it look more like a function,
> >> possibly just like this:
> >>
> >> #define FastPathLockSlotsPerBackend() \
> >> (FP_LOCK_SLOTS_PER_GROUP * FastPathLockGroupsPerBackend)
> >>
> >> Or do you have another suggestion?
> >
> > That'd work for me.
> >
>
> Attached is a patch doing this, but considering it has nothing to do
> with the shmem sizing, I wonder if it's worth it.

Yes.

Greetings,

Andres Freund