Re: Make NUM_XLOGINSERT_LOCKS configurable

On Tue, Jan 09, 2024 at 09:38:17PM -0500, Tom Lane wrote:
> Making it an actual GUC would carry nontrivial costs, not least that
> there are hot code paths that do "foo % NUM_XLOGINSERT_LOCKS" which
> would go from a mask operation to a full integer divide.  We are
> unlikely to consider that on the basis of an unsupported assertion
> that there's a performance gain under unspecified conditions.
> 
> Even with data to justify a change, I think it'd make a lot more sense
> to just raise the constant value.

This suggestion has showed up more than once in the past, and WAL
insertion is a path that can become so hot under some workloads that
changing it to a GUC would not be wise from the point of view of
performance.  Redesigning all that to not require a set of LWLocks
into something more scalable would lead to better result, whatever
this design may be.
--
Michael