Re: Should we cacheline align PGXACT?

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> ... Maybe that difference matters to the memory prefetching
> controller, I dunno, but it seems funny that we did the PGXACT work to
> reduce the number of cache lines that had to be touched in order to
> take a snapshot to improve performance, and now we're talking about
> increasing it again, also to improve performance.

Yes. I was skeptical that the original change was adequately proven
to be a good idea, and I'm even more skeptical this time. I think
every single number that's been reported about this is completely
machine-specific, and likely workload-specific too, and should not
be taken as a reason to do anything.

My druthers at this point would be to revert the separation on code
cleanliness grounds and call it a day, more or less independently of any
claims about performance. I'd be willing to talk about padding PGPROC
to some reasonable stride, but I remain dubious that any changes of
that sort would have a half-life worth complicating the code for.

regards, tom lane