Expected lifetime of software?

[Eric S. Raymond]

Hal Murray <hmurray at megapathdsl.net>:
> 
> How long do we expect our code to last?  Or perhaps more importantly, how 
> long do our users expect it to last?

I expect it to last around the same among of time the ancestral codebase
already has, which is about 35 years.

I'm not pulling this estimate out of a hat.  "It will last about as long 
as it already has" is, as it turns out, a pretty good heuristic for systems
that evolve under selection.

> If the time stamp on the wire wraps in 2036, how far back do we have to get 
> ready and/or when should we start announcing that we are or are/not ready?

Apparently you don't understand the solution Dave Mills already
embedded in the design. This surprises me.

Here's how I think it works:

Instances of ntpd with different pivot points can synchronize because
maximum time skew between servers is much smaller than the modulus of the
NTP calendar.  Above certain skew, the code says "uh oh, looks like
I'm hearing from a server with an epoch other that mine. That means
I need to do calendar aithmetic to figure out which epoch assuption
will minimze the skew".

We don't necessarily have to do much of anything except, for maximum
safety;s sake, update the pivot point at approximately half-cycle
intervals (that is, roughly every 34 years).
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