[systemd-devel] Support for large applications

[Zbigniew Jędrzejewski-Szmek]

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.

Zbyszek