Re: Direct I/O

On Sun, Apr 09, 2023 at 02:45:16PM -0700, Andres Freund wrote:
> On 2023-04-08 21:29:54 -0700, Noah Misch wrote:
> > On Sat, Apr 08, 2023 at 11:08:16AM -0700, Andres Freund wrote:
> > > On 2023-04-07 23:04:08 -0700, Andres Freund wrote:
> > > > If you look at log_newpage_range(), it's not surprising that we get this error
> > > > - it pins up to 32 buffers at once.
> > > > 
> > > > Afaics log_newpage_range() originates in 9155580fd5fc, but this caller is from
> > > > c6b92041d385.
> > 
> > > > Do we care about fixing this in the backbranches? Probably not, given there
> > > > haven't been user complaints?
> > 
> > I would not.  This is only going to come up where the user goes out of the way
> > to use near-minimum shared_buffers.
> 
> 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?