Jordan Brown writes:
> > I'll argue that anything that sents the same set of flags to the same
> > state ought to be time-invariant, if it's going to be comprehensible
> > to mere mortals.
>
> I am not quite sure that I follow your point. How you get from point A
> to point B can be quite important.
I agree that the order of operations along the path is important.
I'm saying that I don't think you should end up in a different stable
(long-term) state if the same set of flags are set. In other words,
this:
svcadm disable foo/top-one
svcadm enable foo/a-depends-on-top-one
svcadm enable foo/b-depends-on-top-one
should result in the same long-term state as:
svcadm enable foo/a-depends-on-top-one
svcadm enable foo/b-depends-on-top-one
svcadm disable foo/top-one
> > At this point, the question I'm asking is whether you should be able
> > to enter "offline" state in both orders or just one. I think entering
> > it in just one order (failure-like semantics) makes more sense.
>
> Here's an analogy:
>
> You can get the system from fully running to powered off in two ways:
I'm not so sure that analogy works too well. One of the clear
side-effects of losing power is that RAM is cleared out and in-flight
disk transactions are gone.
That's not true of the state of the dependent services after a service
failure. Those services still get a chance to shut themselves down in
an "orderly" way, if they're still able to do that.
As long as we have to handle the case where a dependency goes away
(and the service has to go into "offline" state), I think we ought to
be consistent about handling that case.
> They both end up at the same point - system is powered off - so they're
> equivalent, right? Why do we bother with all of this orderly-shutdown
> stuff, when we have to handle the powerfail case anyway?
Not the same; all services lose state on the power-off case, not just
the one that failed.
--
James Carlson, Solaris Networking <james.d.carlson at sun.com>
Sun Microsystems / 35 Network Drive 71.232W Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677
