Bug#679853: general: Too much downtime during a big dist-upgrade - avoidable with snapshots

[Goswin von Brederlow <goswin-v-b@web.de>]

On Mon, Jul 02, 2012 at 08:27:05PM +0600, Alexander E. Patrakov wrote:
> > While it might work for some, there's a much simpler way to minimize
> > daemon downtime: Avoid stopping a daemon in the prerm, and instead
> > restart it in the postinst. Downtime then becomes < 1 second per daemon
> > (less than a kexec reboot).
> > However, the daemon then needs to be audited to ensure that it will
> > continue to work while its foundation is being upgraded underneath it.
> 
> Yes, you seem to be right here. That's what I did for my own
> proprietary daemon that also runs on my debian servers, and it works
> well enough (except that I need to restart it manually when the shared
> libraries it uses receive security updates - but that's OK for me).
> 
> So in reality, I am on the fence. The quoted solution is easier and it
> seems to work well enough. But for some reason, freedesktop folks
> invented this for desktop systems:
> http://fedoraproject.org/wiki/Features/OfflineSystemUpdates . From
> what I have understood, the motivation is that there is no way to get
> a consistent state except by rebooting - which partially corresponds
> to your case of non-audited daemons. Basically, it looks like they
> gave up, that's why I proposed a complicated solution based on the
> same shaky (at least for servers) assumption that it is the best to
> avoid updating packages on a live system.
> 
> As for the issue of merging files e.g. in /etc - the objection is
> valid if there is a valid source of such changes (and IMHO indeed, it
> would be too radical to ban any manual changes in /etc between the
> upgrade and the reboot).
> 
> Also, for anyone reading this bug, I would like to stress that I
> consider it an issue only for systems running the testing
> distribution, because big dist-upgrades are not frequent in stable.
> 
> -- 
> Alexander E. Patrakov

I think that goes along with "There is no way to update but to reinstall."
for most non-Debian based distributions.

Debian has always allowed updating instead of reinstalling and updating
without rebooting. Any system to prepare an update system in the
background and then reboot into the new state will at most be an
alternative. Certainly something nice to have but the it will probably
be like vi/emacs. Half the people like one way, the other the other way.
And the two shall never meet.

MfG
	Goswin