Re: backend hangs at immediate shutdown (Re: Back-branch update releases coming in a couple weeks)

On Fri, Jun 21, 2013 at 2:55 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> More generally, what do we think the point is of sending SIGQUIT
>> rather than SIGKILL in the first place, and why does that point cease
>> to be valid after 5 seconds?
>
> Well, mostly it's about telling the client we're committing hara-kiri.
> Without that, there's no very good reason to run quickdie() at all.

That's what I thought, too. It seems to me that if we think that's
important, then it's important even if it takes more than 5 seconds
for some reason.

> A practical issue with starting to send SIGKILL ourselves is that we
> will no longer be able to reflexively diagnose "server process died
> on signal 9" as "the linux OOM killer got you". I'm not at all
> convinced that the cases where SIGQUIT doesn't work are sufficiently
> common to justify losing that property.

I'm not, either. Maybe this question will provoke many indignant
responses, but who in their right mind even uses immediate shutdown on
a production server with any regularity? The shutdown checkpoint is
sometimes painfully long, but do you really want to run recovery just
to avoid it? And in the rare case where an immediate shutdown fails
to work, what's wrong will "killall -9 postgres"?

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company