Re: Scaling shared buffer eviction

On 2014-10-02 10:56:05 -0400, Robert Haas wrote:
> On Thu, Oct 2, 2014 at 10:44 AM, Andres Freund <andres@2ndquadrant.com> wrote:
> > On 2014-10-02 10:40:30 -0400, Robert Haas wrote:
> >> On Thu, Oct 2, 2014 at 10:36 AM, Andres Freund <andres@2ndquadrant.com> wrote:
> >> >> OK.
> >> >
> >> > Given that the results look good, do you plan to push this?
> >>
> >> By "this", you mean the increase in the number of buffer mapping
> >> partitions to 128, and a corresponding increase in MAX_SIMUL_LWLOCKS?
> >
> > Yes. Now that I think about it I wonder if we shouldn't define MAX_SIMUL_LWLOCKS like
> > #define MAX_SIMUL_LWLOCKS       (NUM_BUFFER_PARTITIONS + 64)
> > or something like that?
> 
> Nah.  That assumes NUM_BUFFER_PARTITIONS will always be the biggest
> thing, and I don't see any reason to assume that, even if we're making
> it true for now.

The reason I'm suggesting is that NUM_BUFFER_PARTITIONS (and
NUM_LOCK_PARTITIONS) are the cases where we can expect many lwlocks to
be held at the same time. It doesn't seem friendly to users
experimenting with changing this to know about a define that's private
to lwlock.c.
But I'm fine with doing this not at all or separately - there's no need
to actually do it together. 

Greetings,

Andres Freund

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