On Thu, Apr 14, 2011 at 1:26 AM, Tomas Vondra <tv@fuzzy.cz> wrote:
> Workload A: Touches just a very small portion of the database, to the
> 'active' part actually fits into the memory. In this case the cache hit
> ratio can easily be close to 99%.
>
> Workload B: Touches large portion of the database, so it hits the drive
> very often. In this case the cache hit ratio is usually around RAM/(size
> of the database).
You've answered it yourself without even realized it.
This particular factor is not about an abstract and opaque "Workload"
the server can't know about. It's about cache hit rate, and the server
can indeed measure that.