Re: pgsql: Add kqueue(2) support to the WaitEventSet API.

On Thu, Feb 20, 2020 at 8:24 PM Michael Paquier <michael(at)paquier(dot)xyz> wrote:
> On Wed, Feb 05, 2020 at 04:59:10AM +0000, Thomas Munro wrote:
> > Add kqueue(2) support to the WaitEventSet API.
> >
> > Use kevent(2) to wait for events on the BSD family of operating
> > systems and macOS. This is similar to the epoll(2) support added
> > for Linux by commit 98a64d0bd.
>
> Worth noting this issue with the test suite of postgres_fdw for
> buildfarm animal coypu, running on NetBSD:
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=coypu&dt=2020-02-19%2023%3A01%3A01
> +ERROR: kqueue failed: Too many open files

Hmm. So coypu just came back after 48 days, and the new kqueue() code
fails for process 19829 after successfully running 265 log lines'
worth of postgres_fdw tests, because it's run out of file
descriptors. I can see that WaitLatchOrSocket() actually could leak
an epoll/kqueue socket if WaitEventSetWait() raises an error, which is
interesting, but apparently not the explanation here because we don't
see a preceding error report. Another theory would be that this
machine has a low max_safe_fds, and NUM_RESERVED_FDS is only just
enough to handle the various sockets that postgres_fdw.sql creates and
at some point kqueue()'s demand for just one more pushed it over the
edge. From the error text and a look at the man page for errno, this
error is EMFILE (per process limit, which could be as low as 64)
rather then ENFILE (system limit).

Remi, any chance you could run gmake installcheck under
contrib/postgres_fdw on that host, to see if this is repeatable? Can
you tell us about the relevant limits? Maybe ulimit -n (for the user
that runs the build farm), and also sysctl -a | grep descriptors,
sysctl -a | grep maxfiles?