Re: Increased iowait and blk_read_time with higher shared_buffers

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