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From: Thomas Munro <thomas.munro@gmail.com>
Date: Thu, 7 Aug 2025 03:03:57 +1200
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Subject: Re: [PATCH] OAuth: fix performance bug with stuck multiplexer events
To: Jacob Champion <jacob.champion@enterprisedb.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Daniel Gustafsson <daniel@yesql.se>,
	Peter Eisentraut <peter@eisentraut.org>
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On Tue, Aug 5, 2025 at 3:24=E2=80=AFAM Jacob Champion
<jacob.champion@enterprisedb.com> wrote:
> On Mon, Aug 4, 2025 at 7:53=E2=80=AFAM Thomas Munro <thomas.munro@gmail.c=
om> wrote:
> > [FYI, I'm looking into this and planning to post a review in 1-2 days..=
.]

0001:

So, the problem is that poll(kqueue_fd) reports POLLIN if any events
are queued, but level-triggered events are only rechecked and possibly
cancelled if you actually call kevent().  Hmm, what if you just called
kevent() with an output array of size one?

 * If it returns 0, that means it has rechecked all queued
level-triggered events and booted them all out because they are no
longer true.  poll(fd) won't report POLLIN until one of them is queued
again.

 * If it returns 1, then it stopped on the first level-triggered event
that it rechecked and found to be still true.  Who cares if there are
more that didn't get rechecked?  poll(fd) will report POLLIN either
way, and that's what you want.