Re: CLOG contention

Excerpts from Simon Riggs's message of jue ene 05 16:21:31 -0300 2012:
> On Thu, Jan 5, 2012 at 7:12 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> > On Thu, Jan 5, 2012 at 11:10 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> >> Let's commit the change to 32.
> >
> > I would like to do that, but I think we need to at least figure out a
> > way to provide an escape hatch for people without much shared memory.
> > We could do that, perhaps, by using a formula like this:
> >
> > 1 CLOG buffer per 128MB of shared_buffers, with a minimum of 8 and a
> > maximum of 32
>
> We're talking about an extra 192KB or thereabouts and Clog buffers
> will only be the size of subtrans when we've finished.

Speaking of which, maybe it'd be a good idea to parametrize the subtrans
size according to the same (or a similar) formula too. (It might be
good to reduce multixact memory consumption too; I'd think that 4+4
pages should be more than sufficient for low memory systems, so making
those be half the clog values should be good)

So you get both things: reduce memory usage for systems on the low end,
which has been slowly increasing lately as we've added more uses of SLRU,
and more buffers for large systems.

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