On Fri, 2004-10-22 at 21:45, Tom Lane wrote:
> Jan Wieck <JanWieck@Yahoo.com> writes:
> > What do you think about my other theory to make C actually 2x effective
> > cache size and NOT to keep T1 in shared buffers but to assume T1 lives
> > in the OS buffer cache?
>
> What will you do when initially fetching a page? It's not supposed to
> go directly into T2 on first use, but we're going to have some
> difficulty accessing a page that's not in shared buffers. I don't think
> you can equate the T1/T2 dichotomy to "is in shared buffers or not".
>
Yes, there are issues there. I want Jan to follow his thoughts through.
This is important enough that its worth it - there's only a few even
attempting this.
> You could maybe have a T3 list of "pages that aren't in shared buffers
> anymore but we think are still in OS buffer cache", but what would be
> the point? It'd be a sufficiently bad model of reality as to be pretty
> much useless for stats gathering, I'd think.
>
The OS cache is in many ways a wild horse, I agree. Jan is trying to
think of ways to harness it, whereas I had mostly ignored it - but its
there. Raw disk usage never allowed this opportunity.
For high performance systems, we can assume that the OS cache is ours to
play with - what will we do with it? We need to use it for some
purposes, yet would like to ignore it for others.
--
Best Regards, Simon Riggs
