[vox] [fwd] [svlug] mission critical computing and air safety

[Ken Bloom]

On Wed, Sep 22, 2004 at 12:30:48PM -0700, Rob Rogers wrote:
> On Wed, Sep 22, 2004 at 11:36:47AM -0700, Tim Riley wrote:
> > On Wed, 2004-09-22 at 10:30, Bill Kendrick wrote:
> > > Here's a nice long post with some more details about the air
> > > traffic issue last week (and his thoughts on the Windows
> > > conversions) from Rick Kwan over at SVLUG.  Just thought it was
> > > interesting reading...
> > 
> > Sure is an interesting read. It seems like a memory leak in
> > the application caused the problem. However, are memory leaks
> > so common that they should be expected? Should the operating
> > system return leaked memory to the memory pool? Should a person
> > have to reboot a computer every month to reset leaked memory?
> 
> Actually, I don't believe it has anything to do with memory leaks
> per se. The text of the article says "The servers are timed to shut
> down after 49.7 days of use in order to prevent a data overload" I
> think they're using "data overload" here in place of something more
> technical that might confuse the average reader.  The actual problem
> (well, I don't actually know with 100% certainty, but it's not the
> first time I've seen the a 49.7 day problem) is that somewhere in
> the application there's a 32 bit counter being used. Doing a little
> math 2^32 = 4.294e09. Divide that by 24 (hours) 60 (minutes) 60
> (seconds) and 1000 (miliseconds) gives you 49.7 ... hence the "data
> overload" being a time based counter rolling over to zero.
> 
> The 49.7 day problem is actually a known problem with Windows 95 and
> 98 (and possibly others), where they would reboot after that time
> period because of an internal Windows counter. Win2K doesn't have
> this problem itself, but I have seen applications running on Win2K
> that had this problem. In particular a developer friend of mine came
> to me wondering why one app in particular started acting differently
> and needed to be shut down and restarted every seven weeks. He was
> the one person I knew who had more than 6 months uptime on a windows
> desktop box.

So this is where we take note and say that had the air traffic control
system been open source, it could have been recompiled against the
appropriate size data type, and would be able to record data
approximately forever. :-)

--Ken Bloom

-- 
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G'mar Chatima Tova
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