[erlang-questions] auto-syncing mnesia after a network split

Felix Hamilton <>
Tue Dec 2 22:47:19 CET 2008


I have used NTP (the Network Time Protocol) quite effectively to sync
timestamps in widely distributed systems with a fairly high degree of
accuracy.

It may be that using an NTP server and clients to provide time syncing
for Mnesia may be a valuable addition - NTP resolution can get quite
high (read way more than you need) if you have redundant servers.

Is there an NTP project for Erlang as yet? If not, that might be a
project that would provide quite a few benefits to the community ...

/Felix

On Tue, Dec 2, 2008 at 1:30 PM, David Mercer <> wrote:
> On Tuesday, December 02, 2008, Joel Reymont wrote:
>
>> On Dec 2, 2008, at 8:24 PM, David Mercer wrote:
>>
>> > How do you handle unsynched clocks on the two nodes?
>>
>> I don't know. Should they go out of sync during the split if the split
>> is short?
>
> Aren't clocks always out of synch?  I thought it was impossible to perfectly
> synch clocks due to signal transmission times, at least over a standard
> network.  Even if the clocks were precisely in-synch, same problem if the
> same transaction is received by the two nodes a microsecond apart: they'll
> have different timestamps.  I wonder if adding some sort of GUID would solve
> the problem...  Maybe a client-generated ID.
>
> Another thought is that two transactions can be received by different nodes
> in different order, resulting in different vnums for the same transactions
> on different nodes.
>
> Cheers,
>
> David.
>
>
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