time syncronization in erlang cluster
Primanathan Reddy [ MTN - Innovation Centre ]
Fri Jan 9 09:51:07 CET 2004
Thanks for the helpful info on now().
I'm going to try NTP.
Will keep the list updated on how it turns out.
From: Ulf Wiger [mailto:]
Sent: Thursday, 08 January 2004 8:09 PM
To: WILLIAMS Dominic; Erlang (E-mail)
Subject: Re: time syncronization in erlang cluster
On Thu, 8 Jan 2004 14:19:46 +0100, WILLIAMS Dominic
> Hi Pete,
>> What is the platform? If you're using a flavour of UNIX, you
>> may wish to use NTP (network time protocol RFC 1305) and
>> bypass Erlang for synchronisation. I imagine there are NTP
>> clients and servers implemented for most platforms.
> Indeed, including Windows (just don't use Microsoft's built-in
> version, which is simplified, if you want the features I
> described in my previous post).
> However, this doesn't work, at least for Erlang systems running
> uninterruptedly, if the Erlang runtime only gets the system time
> at start-up...
This is how erlang:now() works.
At startup, it samples the system time, and then it starts running
loosely coupled to the system time. That is, it periodically samples
the system time and makes small adjustments (+/- 1%) so that it
will eventually converge with the actual system time ("eventually"
may be an arbitrarily long time, depending on what happens to the
So to answer your initial question: you cannot synchronize erlang:now(),
since it is designed to adjust itself to e.g. NTP, while preserving the
property that subsequent calls to erlang:now() should always return
unique values in increasing order.
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