Re: [HACKERS] kqueue

On Tue, Jan 21, 2020 at 8:03 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I observe very similar behavior on FreeBSD/amd64 12.0-RELEASE-p12,
> so it's not just macOS.

Thanks for testing. Fixed by handling the new
exit_on_postmaster_death flag from commit cfdf4dc4.

On Tue, Jan 21, 2020 at 5:55 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Thomas Munro <thomas(dot)munro(at)gmail(dot)com> writes:
> > [ 0001-Add-kqueue-2-support-for-WaitEventSet-v13.patch ]
>
> I haven't read this patch in any detail, but a couple quick notes:
>
> * It needs to be rebased over the removal of pg_config.h.win32
> --- it should be touching Solution.pm instead, I believe.

Done.

> * I'm disturbed by the addition of a hunk to the supposedly
> system-API-independent WaitEventSetWait() function. Is that
> a generic bug fix? If not, can we either get rid of it, or
> at least wrap it in "#ifdef WAIT_USE_KQUEUE" so that this
> patch isn't inflicting a performance penalty on everyone else?

Here's a version that adds no new code to non-WAIT_USE_KQUEUE paths.
That code deals with the fact that we sometimes discover the
postmaster is gone before we're in a position to report an event, so
we need an inter-function memory of some kind. The new coding also
handles a race case where someone reuses the postmaster's pid before
we notice it went away. In theory, the need for that could be
entirely removed by collapsing the 'adjust' call into the 'wait' call
(a single kevent() invocation can do both things), but I'm not sure if
it's worth the complexity. As for generally reducing syscalls noise,
for both kqueue and epoll, I think that should be addressed separately
by better reuse of WaitEventSet objects[1].

[1] https://www.postgresql.org/message-id/CA%2BhUKGJAC4Oqao%3DqforhNey20J8CiG2R%3DoBPqvfR0vOJrFysGw%40mail.gmail.com