On Wed, Apr 13, 2011 at 5:26 PM, 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).
I've had this kind of split-brain operation in the past, where 99% of
all accesses would be cached, and the 1% that weren't needed their own
tuning. Luckily you can tune by user (alter user set random_page_cost
etc) so I was able to do that. One of the best features of pgsql
imnsho.