Re: Excessive PostmasterIsAlive calls slow down WAL redo

On 2018-04-05 14:39:27 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > ISTM the better approach would be to try to reduce the cost of
> > PostmasterIsAlive() on common platforms - it should be nearly free if
> > done right.
>
> +1 if it's doable.
>
> > One way to achieve that would e.g. to stop ignoring SIGPIPE and instead
> > check for postmaster death inside the handler, without reacting to
> > it. Then the the actual PostmasterIsAlive() checks are just a check of a
> > single sig_atomic_t.
>
> AFAIR, we do not get SIGPIPE on the postmaster pipe, because nobody
> ever writes to it. So this sketch seems off to me, even assuming that
> not-ignoring SIGPIPE causes no problems elsewhere.

Yea, you're probably right. I'm mostly brainstorming here.

(FWIW, I don't think not ignoring SIGPIPE would be a huge issue if we
don't immediately take any action on its account)

> While it's not POSIX, at least some platforms are capable of delivering
> a separate signal on parent process death. Perhaps using that where
> available would be enough of an answer.

Yea, that'd work on linux. Which is probably the platform 80-95% of
performance critical PG workloads run on. There's
JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE on windows, which might also work,
but I'm not sure it provides enough opportunity for cleanup.

Greetings,

Andres Freund