Re: First draft of PG 17 release notes

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".

David