Re: Multiple buffer cache?

On Sat, Feb 06, 2010 at 02:44:32PM +0100, C?dric Villemain wrote:
> 2010/2/6 Bret S. Lambert <bret(dot)lambert(at)gmail(dot)com>:
> > On Fri, Feb 05, 2010 at 11:41:13PM +0200, Alexei Vladishev wrote:
> >> Greetings,
> >>
> >> Is there a way of configuring PostgreSQL so that one specific table would
> >> use, say, 4GB of buffer cache while other tables would use the rest?
> >>
> >> I would like to keep the table and its indexes always in "hot"
> >> state, so that
> >> other queries won't pollute this part of the buffer cache. It would ensure
> >> reliable performance and much less disk IOPS working with the table.
> >
> > Fiddling with the buffer cache like that would require some sort of
> > OS support, if I'm not mistaken in what you're asking for.
> >
> > And then, even if the support is there, you'd need to outline exactly
> > how you're planning on pushing this button.
> >
> > Specifically, what's your usage pattern that would make this a
> > win for you?
> >
> > If the table and its indexes can already fit into the buffer cache,
> > and it's as commonly accessed as you think it is, the OS should
> > probably have it cached anyway.
>
> that's all true.
>
> I am working on pgfincore which allow in some way to prepare buffer cache.
> You need pg > 8.4 and linux (probably working with bsd too)

Why do something with a non-portable interface? Most OSes support
coherently mmap(2)'ing disk blocks into memory; in fact, I'm somewhat
taken aback that the postgres buffer cache isn't implemented in that
manner, but I'm willing to give the devs credit for having not done
so for good reasons.

>
> I don't consider it ready fo rproduction, but fine for debugging
> things, if you reall care the buffer cache preload, tell me, I'll
> stabilize the code in a shorter time ;)
> http://villemain.org/projects/pgfincore
>
> >
> >>
> >> Is it possible?
> >>
> >> Thanks for any hints!
> >>
> >> Alexei
> >>
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>
>
>
> --
> C?dric Villemain