Re: Scaling shared buffer eviction

On 2014-09-25 09:34:57 -0500, Merlin Moncure wrote:
> On Thu, Sep 25, 2014 at 9:14 AM, Andres Freund <andres@2ndquadrant.com> wrote:
> >> Why stop at 128 mapping locks?   Theoretical downsides to having more
> >> mapping locks have been mentioned a few times but has this ever been
> >> measured?  I'm starting to wonder if the # mapping locks should be
> >> dependent on some other value, perhaps the # of shared bufffers...
> >
> > Wrong way round. You need to prove the upside of increasing it further,
> > not the contrary. The primary downside is cache hit ratio and displacing
> > other cache entries...
> 
> I can't do that because I don't have the hardware.

One interesting part of this is making sure it doesn't regress
older/smaller machines. So at least that side you could check...

> what's wrong with trying it out?

If somebody is willing to do it: nothing. I'd just much rather do the,
by now proven, simple change before starting with more complex
solutions.

Greetings,

Andres Freund

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