On Wed, May 04, 2005 at 09:11:37AM +0100, Julian Scarfe wrote:
> So if I'm alone in my office, fall asleep, then wake up wondering whether 
> I'm still boss (hey, this is an analogy, give me some poetic licence ;-)), 
> I can't tell the difference between a situation where my colleagues have 
> decided to leave me in peace to get some work done, and one where my 
> colleagues have locked the door to my office and replaced me as boss 
> because I was asleep -- unless of course I try the door, which breaks the 
> paradigm by turning me into a door-checker.  Fair enough, but if the latter 
> situation, it would have been polite for them to have sent me an email 
> saying "you're fired".

The problem is more like Descartes doing all of what you just said --
you can't be sure that the evil demon isn't fooling with you, either. 
Because you don't know whether all your communication has been cut
off (because "cut off" is defined by what _others_ see, not what you
do), the interpretation of "I didn't get an email" is indeterminate:
it may mean, "they didn't send one," or it might mean, "it was sent
and I didn't get it."  And without also being a door-checker, network
monitor, electricity monitor, gaps in space-time checker, and other
such things, you have no way of finding out.

> Isn't there a useful middle ground?  A failover that includes an 
> asynchronous message for the old origin to say "you're fired", or more 
> precisely, "you are no longer the origin for set id = 1".  Perhaps I'm 
> missing the point.  Perhaps MOVE SET does exactly that(?)

It doesn't, no.  And while everyone would agree, I think, that a
middle ground would be nice, there's no way to do it that will work,
and that won't run the risk of the system coming "back online" in the
disastrous way you're worried about.

A

-- 
Andrew Sullivan  | ajs at crankycanuck.ca
In the future this spectacle of the middle classes shocking the avant-
garde will probably become the textbook definition of Postmodernism. 
                --Brad Holland