Re: Avoiding repeated snapshot computation

On Saturday, November 26, 2011 11:39:23 PM Robert Haas wrote:
> On Sat, Nov 26, 2011 at 5:28 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > On Saturday, November 26, 2011 09:52:17 PM Tom Lane wrote:
> >> I'd just as soon keep the fields in a logical order.
> >
> > Btw, I don't think the new order is necessarily worse than the old one.
>
> You forget to attach the benchmark results.
>
> My impression is that cache lines on modern hardware are 64 or 128
> *bytes*, in which case this wouldn't matter a bit.
All current x86 cpus use 64bytes. The 2nd 128bit reference was a typo. Sorry
for that.
And why is 72=>56 *bytes* (I even got that one right) not relevant for 64byte
cachelines?

And yea. I didn't add benchmark results. I don't think I *have* to do that
when making suggestions to somebody trying to improve something specific. I
also currently don't have hardware where I can sensibly run at a high enough
concurrency to see that GetSnapshotData takes ~40% of runtime.
Additional cacheline references around synchronized access can hurt to my
knowledge...

Andres