Re: Optimizing Read-Only Scalability

On Thu, 2009-05-14 at 14:06 -0400, Robert Haas wrote:

> Supposing that the patch can be shown to improve performance for
> all-read-only workloads, and supposing further that the patch can be
> shown to have no material negative impact on write-heavy workloads, it
> would also be interesting to throw in a bit of scattered write traffic
> and see whether that completely negates the benefit or not.

If you have a workload consisting of high volume single/few row lookups
(OLRP), then ISTM that the majority of data cache line accesses will be
on the procarray, especially so when we have many sessions. More to the
point, MySQL would not need to access an equivalent data structure and
so Postgres would access much more memory.

The way I understand it, typically 4 CPUs at a time will be able to
access that memory at the same time. If they can skip that part
entirely, then we will get better scalability.

Anyway, I'd be indebted to anyone that can shed more light on the
hardware technical details in my above paragraphs. We'll learn something
either way.

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Training, Services and Support