Re: Increased iowait and blk_read_time with higher shared_buffers

Thanks Tom, that makes a lot of sense. Given we're seeing low iowait and
blk_read_time at 4GB shared_buffers, sounds like we should just declare
victory here and be happy with that setting?

On Wed, Dec 14, 2022 at 10:27 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Jordan Hurwich <jhurwich(at)pulsasensors(dot)com> writes:
> > I'm familiar with the article you linked to, and part of my surprise is
> > that with these 32GB RAM machines we're seeing better performance at
> 12.5%
> > (4GB) than the commonly recommended 25% (8GB) of system memory for
> > shared_buffers. Your notes about disk read stats from Postgres
> potentially
> > actually representing blocks read from the OS cache make sense, I just
> > imagined that Postgres would be better at managing the memory when it was
> > dedicated to it via shared_buffers than the OS (obviously with some point
> > of diminishing returns); and I'm still hoping there's some Postgres
> > configuration change we can make that enables better performance through
> > improved utilization of shared_buffers at the commonly recommended 25% of
> > system memory.
>
> Keep in mind that 25% was never some kind of golden number. It is
> a rough rule of thumb that was invented for far smaller machines than
> what you're talking about here.
>
> regards, tom lane
>