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Date: Fri, 06 Dec 2013 01:15:52 +0000
From: Laurent Bercot <>
Subject: Re: [PATCHv2] Add support for leap seconds in zoneinfo files

> Regarding the unfortunate coupling of timezone and leapsecond data
> into a single file, do the zoneinfo files with leapseconds have their
> timezone transition times stored in POSIX time or TAI?

  TAI-10 (the 10 seconds offset is so it's the same as POSIX time
before 1972). As I said, it's the only behaviour that makes sense:
we're counting a number of seconds and we want it to be unambiguous.
POSIX time would create an ambiguity for the very moment when a leap
second happens, which defeats the purpose.

> It seems really inconsistent to me that someone who's pedantic enough
> to care about leap seconds wouldn't care about having to "reboot" (I
> use this term loosely) their servers/daemons when a new one is
> announced. If you're ok with that discontinuity what's wrong with just
> losing the leap second?

  Leap seconds are announced in advance; it's easy to plan a "reboot"
over a 6-month (or larger) period before the actual leap second happens.
  On the other hand, no planning will prevent the kernel from crashing,
make from getting confused, CLOCK_REALTIME-based event loops from failing
when the system clock hiccups under their feet.

  Locking and an advanced updating system to the leap second table could
be designed, so that long-lived processes don't even have to restart when
a new leap second is announced. But frankly, it just doesn't seem worth the
trouble. Restarting a process is easy; people who need high availability
usually have several instances of the service and can restart them one by

> At the very least they would have some overhead determining that
> leapseconds aren't in use.

  Indeed, one test at executable start. :)
  Do you have any idea what form this test would take, if we're opting
away from TZ ?


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