Re: shared_buffers performance

"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> Gregory Stark <stark(at)enterprisedb(dot)com> writes:
>> The transition domain where performance drops dramatically as the database
>> starts to not fit in shared buffers but does still fit in filesystem cache.
>
> It looks to me like the knee comes where the DB no longer fits in
> filesystem cache.

That does seem to make a lot more sense. I think I misread the units of the
size of the accounts table. Reading it again it seems to be in the 1.5G-2G
range for the transition which with indexes and other tables might be starting
to stress the filesystem cache -- though it still seems a little low.

I think if I squint I can see another dropoff at the very small scaling
numbers. That must be the point where the database is comparable to the shared
buffers size. Except then I would expect the green and blue curves to be
pushed to the right a bit rather than just havin a shallower slope.

--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
Ask me about EnterpriseDB's On-Demand Production Tuning