[erlang-questions] The upcoming leap second

[Rickard Green]

On Wed, May 13, 2015 at 3:39 PM, Youngkin, Rich
<richard.youngkin@REDACTED> wrote:
> Hi all,
>
> There's an upcoming leap second on June 30th.  There's a bit of buzz about
> how it affects Linux and Java, as well as problems encountered in 2012 [1].
> I was wondering if there are any known issues with Erlang. I searched for
> "erlang leap second" and a few things popped up [2][3]. The link for [3] is
> stale.
>
> Thanks,
> Rich
>
> [1] -
> http://www.networkworld.com/article/2872578/business-continuity/watch-out-for-an-upcoming-leap-second.html
> [2] - http://erlang.org/pipermail/erlang-bugs/2009-April/001254.html
> [3] -
> http://www.erlang.org/documentation/doc-7.0-rc1/erts-7.0/doc/html/time_correction.html
>
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>

The Erlang runtime system as such will be able to handle it. This
assuming that the only effect the leap second have on the OS is a
change in system time (such as for example a freeze of time for a
second).

On pre OTP 18 systems there are two scenarios:

- Time correction is enabled: The frequency of the Erlang system time
will temporarily change (with 1%) in order to slowly align Erlang
system time with OS system time.
- Time correction is disabled: Erlang system time immediately follows
OS system time as long as OS system time does not go backwards. If OS
system time goes backwards, Erlang system time will freeze until OS
system time has caught up.

What the total effect will be on your system depends on how your
Erlang code reacts to the above.

On OTP 18 systems there are a few more scenarios depending on
configuration. See
http://www.erlang.org/documentation/doc-7.0-rc2/erts-7.0/doc/html/time_correction.html
(the rc1 version was removed when we published rc2).

Regards,
Rickard

-- 
Rickard Green, Erlang/OTP, Ericsson AB