Re: [RFC, POC] Don't require a NBuffer sized PrivateRefCount array of local buffer pins

Andres Freund wrote:
> On 2014-08-26 22:19:47 -0400, Tom Lane wrote:
> > Andres Freund <andres(at)2ndquadrant(dot)com> writes:

> > I would say that the issue most deserving of performance testing is your
> > sizing of the linear-search array --- it's not obvious that 8 is a good
> > size.
>
> It's about the size of a cacheline on all common architectures, that's
> how I found it. I don't think it makes a very big difference whether we
> make it 4 or 12, but outside of that range I think it'll be unlikely to
> be beneficial. The regression tests never go about three or four pins or
> so currently, so I think that's a number unlikely to regularly be
> crossed in practice.

FWIW scanning a minmax index will keep three pages pinned IIRC
(metapage, current revmap page, current regular page).

--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services