Re: PostgreSQL and HugePage

On Wed, Oct 20, 2010 at 12:28:25PM -0700, Greg Stark wrote:
> On Wed, Oct 20, 2010 at 12:17 PM, Greg Stark <gsstark(at)mit(dot)edu> wrote:
> > I don't think it's a big cost once all the processes
> > have been forked if you're reusing them beyond perhaps slightly more
> > efficient cache usage.
>
> Hm, this site claims to get a 13% win just from the reduced tlb misses
> using a preload hack with Pg 8.2. That would be pretty substantial.
>
> http://oss.linbit.com/hugetlb/

That was my motivation in trying a patch. TLB misses can be a substantial
overhead. I'm not current on the state of play, but working at Sun's
benchmark lab on a DB TPC-B benchmark something for the first generation
of MP systems, something like 30% of all bus traffic was TLB misses. The
next iteration of the hardward had a much larger TLB.

I have a client with 512GB memory systems, currently with 128GB configured
as postgresql buffer cache. Which is 32M TLB entires trying to fit in the
few dozed cpu TLB slots. I suspect there may be some contention.

I'll benchmark of course.

-dg

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David Gould daveg(at)sonic(dot)net 510 536 1443 510 282 0869
If simplicity worked, the world would be overrun with insects.