[LEAPSECS] Crunching Bulletin B numbers (POSIX time)

[Ian Batten]

On 21 Feb 2011, at 03:32, Paul Sheer wrote:


>> 

>> [...] But so what?  It'll report 00:00:03 Monday when it's "really"

>> 23:59:57 Sunday --- why is this small number of seconds any more

>> important than any other small number of seconds error?  [...]

>> 

> 

> 

> A miss is as good as a mile when a timestamp is an index into a hash

> table.


So let's try to understand your use-case.  Machine A, which is isolated from the outside world and unable to perform leap-second adjustment but maintains a stable clock with a CsRb , is generating hashes, alongside Machine B, which is performing leap-second adjustment via (for the sake of argument) NTP or GPS., and those hashes are being used as indexes into a hash table that both A and B read and write?   Yes, I can see leap-second would cause a problem there, except (a) the engineering design is insane and (b) even if it isn't, TAI is ready and waiting to solve their needs.  Has anyone, anywhere, written a system so stupid and not been locked up?


> 

> These systems don't care whether the event really did happen at

> 12:34:56pm nor whether the clock was a few minutes slow that day.

> 

> But they DO care that they are talking about the SAME event!!!

> 


So how is a leap second (or, more to the point, 120 leap seconds) any different to "a few minutes slow"?   Two systems are communicating.  One applies a leap second the other doesn't know about via nasty slewing over the course of an hour.  Two other systems are communicating.  One loses a second relative to the other through thermal effects.  Describe how an outside observer might distinguish those scenarios given a sequence of timestamps from the systems.  



> 

> Imagine a complex business environment represented by a large block

> diagram. Data, including fields that contain timestamps, propagate

> around this block diagram -


A complex business environment which nonetheless cannot perform one bit of I/O per eighteen months.  A complex business system which nonetheless cannot interact with NTP, MSF/DCF77/WWV or GPS?  I think you're making something up to bolster a point, not referring to any real business environment.

ian