Re: [HACKERS] PATCH: Keep one postmaster monitoring pipe per process

On Thu, Jul 19, 2018 at 10:30 PM, Kyotaro HORIGUCHI
<horiguchi.kyotaro@lab.ntt.co.jp> wrote:
>> Hmm.  Why wait any longer?  The cluster is broken.  Is there some
>> correctness reason to defer shutdown in any of these places?
>
> Well, please don't get me wrong. I don't object to backends' exit
> on postmaster death, rather I'm for it. Maybe the idea of mine
> came from somthing like this (perhaps newer one), in the meaning
> of just why it is working in that way now.
>
> https://www.postgresql.org/message-id/21877.1294946166@sss.pgh.pa.us

Thanks, that was interesting.  It's from *before* the pipe solution
was implemented though so I'm not sure it's relevant: the
exit-as-soon-as-possible camp won that battle, we just missed a few
places.

>> He mentioned that syslogger.c is a special case.  In my patch I added
>> WL_EXIT_ON_PM_DEATH to SysLoggerMain()'s WaitLatch*() calls, because I
>> have to or the new assertion fails.  Hmm, yeah, that's not great
>> because it might discard the last words of other backends.  So here is
>> a new version that treats syslogger.c specially and may have other
>> performance benefits.
>
> Yeah. That seems good. Couldn't we reuse prepared WaitEventSet in
> other places? For example PgstatCollectorMain has the same
> characteristics, where WaitLatchOrSocket is used with fixed
> parameters and waiting on a socket which gets frequent receipts.

+1, but I'm considering that to be a separate project, or I'll never
get this patch committed.  It may be possible to have a small number
of them reused in many places, and it may be possible for
WaitLatchXXX() to reuse them automatically (so we don't have to change
 every call site).

> # Is it intentional that the patch doesn't touch pgstat.c?

Yes.  pgstat.c still uses WL_POSTMASTER_DEATH because it does
something special: it calls pgstat_write_statsfiles() before it exits.

-- 
Thomas Munro
http://www.enterprisedb.com