Re: [RFC] Should we fix postmaster to avoid slow shutdown?

Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com> writes:
> ISTM that this would change the "immediate shutdown" to not save stats
> files anymore. So far, all the shutdown modes are equivalent in terms
> of how they preserve data and system state. They differ only in when
> the hard work happens. This would be a deviation from that principle.

There is that. Up to now, an immediate shutdown request didn't cause
any actual data loss, but now it would. Maybe that's a reason to reject
this whole concept. (Upthread I was thinking that's a behavior we have
anyway, but really we don't: a look through pgstats.c shows that it will
never exit without attempting to write the stats, short of a crash of
the stats collector process itself.)

> Child processes don't distinguish between a SIGQUIT coming from a
> user-initiated immediate shutdown request and a crash-induced
> kill-everyone directive. So there might not be a non-ugly way to
> address that.

It doesn't seem to me that it's a matter of whether the signaling is
adequate; we could fix that. It's a matter of whether you're willing to
have "pg_ctl stop -m immediate" lose stats data.

Although the stats collector was originally conceived as optional,
we depend on it enough now for autovacuum that I'm not sure it'd be a
good thing to have a popularly-used shutdown mode that loses the stats.

regards, tom lane