[systemd-devel] Support for large applications

[Tomasz Torcz]

On Fri, Feb 19, 2016 at 12:49:53PM +0000, Zbigniew Jędrzejewski-Szmek wrote:
> On Fri, Feb 19, 2016 at 01:42:12PM +0100, Michal Sekletar wrote:
> > On Wed, Feb 17, 2016 at 1:35 PM, Avi Kivity <avi at scylladb.com> wrote:
> > 
> > > 3. watchdog during startup
> > >
> > > Sometimes we need to perform expensive operations during startup (log
> > > replay, rebuild from network replica) before we can start serving. Rather
> > > than configure a huge start timeout, I'd prefer to have the service report
> > > progress to systemd so that it knows that startup is still in progress.
> > >
> > 
> > Did you have a look at sd_notify (man 3 sd_notify)? Basically, you can
> > easily patch your service to report status to systemd and tell to
> > systemd exactly when it is ready to serve the clients. Thus you can
> > avoid hacks like huge start timeout you've mentioned.
> 
> I don't think that helps, unless the service "lies" to systemd and
> tells it has finished startup when it really hasn't (systemd would
> ignore watchdog notifications during startup, and would do nothing if
> they stopped coming, so the service has to tell systemd first that it
> has started successfully, for the watchdog to be effective). Doing
> that would fix this issue, but would have that systemd wouldn't know
> that the service is still starting and would for example start
> subsequent jobs.
> 
> I don't think there's a way around the issue short of allowing
> watchdog during startup. Databases which do long recovery are a bit
> special, most programs don't exhibit this kind of behaviour, but maybe
> this case is important enough to add support for it.

  Maybe systemd could ignore watchdog notification during startup UNTIL
first WATCHDOG=1 notification comes? Then normal watchdog logic would kick in.
  This way we retain current logic (ignore watchdog during startup) unless
application WANTS to tickle watchdog during startup.
  Or is it too much magic?

-- 
Tomasz Torcz              ,,If you try to upissue this patchset I shall be seeking
xmpp: zdzichubg at chrome.pl   an IP-routable hand grenade.'' -- Andrew Morton (LKML)