Re: First draft of PG 17 release notes

On Wed, May 15, 2024 at 7:36 AM Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>
> On Wed, May 15, 2024 at 02:03:32PM +1200, David Rowley wrote:
> > On Wed, 15 May 2024 at 13:00, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > >
> > > On Tue, May 14, 2024 at 03:39:26PM -0400, Melanie Plageman wrote:
> > > > "Reduce system calls by automatically merging reads up to io_combine_limit"
> > >
> > > Uh, as I understand it, the reduced number of system calls is not the
> > > value of the feature, but rather the ability to request a larger block
> > > from the I/O subsystem. Without it, you have to make a request and wait
> > > for each request to finish. I am open to new wording, but I am not sure
> > > your new wording is accurate.
> >
> > I think you have the cause and effect backwards. There's no advantage
> > to reading 128KB if you only need 8KB. It's the fact that doing
> > *larger* reads allows *fewer* reads that allows it to be more
> > efficient. There are also the efficiency gains from fadvise
> > POSIX_FADV_WILLNEED. I'm unsure how to jam that into a short sentence.
> > Maybe; "Optimize reading of tables by allowing pages to be prefetched
> > and read in chunks up to io_combine_limit", or a bit more buzzy;
> > "Optimize reading of tables by allowing pages to be prefetched and
> > performing vectored reads in chunks up to io_combine_limit".
>
> Yes, my point is that it is not the number of system calls or system
> call overhead that is the advantage of this patch, but the ability to
> request more of the I/O system in one call, which is not the same as
> system calls.
>
> I can use your wording, but how much prefetching to we enable now?
>

Shouldn't we need to include commit
b5a9b18cd0bc6f0124664999b31a00a264d16913 with this item?

--
With Regards,
Amit Kapila.