Re: PATCH: Keep one postmaster monitoring pipe per process

Hi,

On 2016-09-16 09:55:48 +0200, Marco Pfatschbacher wrote:
> On Thu, Sep 15, 2016 at 12:26:16PM -0700, Andres Freund wrote:
> > Yikes, that's a pretty absurd implementation.
>
> Not when you take into account that it's been written over 20 years ago ;)

Well, that doesn't mean it can't be fixed ;)

> > I'm not quite sure I understand why this an issue here - there shouldn't
> > ever be events on this fd, so why is the kernel waking up all processes?
> > It'd kinda makes sense it'd wake up all processes if there's one
> > waiting, but ... ?
>
> Every read is an event, and that's what PostmasterIsAlive does.

But in most places we only do a PostmasterIsAlive if WaitLatch returns
WL_POSTMASTER_DEATH. The only walreceiver related place that doesn't is
WalRcvWaitForStartPosition(). If that's indeed the cause of your issues
this quite possibly could be fixed by doing the
if (!PostmasterIsAlive())
exit(1);
check not unconditionally, but only after the WaitLatch at the end of
the loop, and only if WL_POSTMASTER_DEATH is returned by WaitLatch()?
That'll be a minor behaviour change for the WALRCV_RESTARTING, but that
seems fine, we'll just loop once more outside (after a quick glance at
least).

Andres