Re: Direct I/O

Hi,

On 2023-04-09 16:40:54 -0700, Noah Misch wrote:
> On Sun, Apr 09, 2023 at 02:45:16PM -0700, Andres Freund wrote:
> > It's not *just* that scenario. With a few concurrent connections you can get
> > into problematic territory even with halfway reasonable shared buffers.
>
> I am not familiar with such cases.  You could get there with 64MB shared
> buffers and 256 simultaneous commits of new-refilenode-creating transactions,
> but I'd still file that under going out of one's way to use tiny shared
> buffers relative to the write activity.  What combination did you envision?

I'd not say it's common, but it's less crazy than running with 128kB of s_b...

There's also the issue that log_newpage_range() is used in number of places
where we could have a lot of pre-existing buffer pins. So pinning another 64
buffers could tip us over.

Greetings,

Andres Freund