Re: Why does backend send buffer size hardcoded at 8KB?

On 2019-07-27 19:10:22 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On 2019-07-27 18:34:50 -0400, Tom Lane wrote:
> >> Yeah. The existing commentary about that is basically justifying 8K
> >> as being large enough to avoid performance issues; if somebody can
> >> show that that's not true, I wouldn't have any hesitation about
> >> kicking it up.
>
> > You think that unnecessary fragmentation, which I did show, isn't good
> > enough? That does have cost on the network level, even if it possibly
> > doesn't show up that much in timing.
>
> I think it is worth doing some testing, rather than just blindly changing
> buffer size, because we don't know how much we'd have to change it to
> have any useful effect.

I did a little test with nttcp between two of our servers (1 Gbit to
different switches, switches connected by 10 Gbit). The difference
between a 1024 byte buffer and a 1460 byte buffer is small but
measurable. Anything larger doesn't make a difference. So increasing the
buffer beyond 8 kB probably doesn't improve performance on a 1 Gbit LAN.

I didn't test 10 Gbit LAN or WAN - those might be different.

hp

--
_ | Peter J. Holzer | we build much bigger, better disasters now
|_|_) | | because we have much more sophisticated
| | | hjp(at)hjp(dot)at | management tools.
__/ | http://www.hjp.at/ | -- Ross Anderson <https://www.edge.org/>