Programming for Power Failures

Programming in South Africa has had to adjust to a whole new set of ground rules. Not only does the broadband connection disconnect itself every 6 hours, thanks to Telkom, but the power can go out at any moment. This makes for interesting database programming.
I am writing a database program for Men's Clinic that helps them process patient bookings and invoices at the clinic level. To tighten up security we only allowed invoices to be made out for today's date. That's all very well if the power is working, but what do you do if the power went off and you went manual for the rest of the day? How do you allow the clinic people to catch up the invoices on the following day, without preventing them from issuing invoices for today as well? An interesting problem. After all Uninterruptible Power Supplies don't last forever. And petrol generators are fine, provided you can buy petrol. Personally, I'd prefer a diesel generator, because you can run it on cooking oil if diesel isn't available.

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