Re: Excessive PostmasterIsAlive calls slow down WAL redo

Greetings,

* Andres Freund (andres@anarazel.de) wrote:
> On 2018-04-05 14:39:27 -0400, Tom Lane wrote:
> > Andres Freund <andres@anarazel.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.
[...]
> > 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.

While I tend to agree that it'd be nice to just make it cheaper, that
doesn't seem like something that we'd be likely to back-patch and I tend
to share Heikki's feelings that this is a performance regression we
should be considering fixing in released versions.

What Alvaro posted up-thread seems like it might be a small enough
change to still be reasonable to back-patch and we can still think about
ways to make PostmasterIsAlive() cheaper in the future.

Thanks!

Stephen