On 2016-09-13 16:08:39 +0300, Heikki Linnakangas wrote:
> So, if I've understood correctly, the purpose of this patch is to improve
> performance on a multi-CPU system, which has the kqueue() function. Most
> notably, FreeBSD?

I think it's not necessarily about the current system, but more about
future uses of the WaitEventSet stuff. Some of that is going to use a
lot more sockets. E.g. doing a parallel append over FDWs.

> I launched a FreeBSD 10.3 instance on Amazon EC2 (ami-e0682b80), on a
> m4.10xlarge instance. That's a 40 core system, biggest available, I believe.
> I built PostgreSQL master on it, and ran pgbench to benchmark:
> pgbench -i -s 200 postgres
> pgbench -M prepared  -j 36 -c 36 -S postgres -T20 -P1

This seems likely to actually seldomly exercise the relevant code
path. We only do the poll()/epoll_wait()/... when a read() doesn't
return anything, but that seems likely to seldomly occur here.  Using a
lower thread count and a lot higher client count might change that.

Note that the case where poll vs. epoll made a large difference (after
the regression due to ac1d7945f86) on linux was only on fairly large
machines, with high clients counts.


Andres Freund

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