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From "Jens Rantil" <>
Subject Re: Multi DC informations (sync)
Date Fri, 19 Dec 2014 10:44:23 GMT

AFAIK, the DC replication is not linearizable. That is, writes are are not replicated according
to a binlog or similar like MySQL. They are replicated concurrently.

To answer you questions:

1 - Replication lag in Cassandra terms is probably “Hinted handoff”. You’d want to check
the status of that.

2 - `nodetool status` is your friend. It will tell you whether the cluster considers other
nodes reachable or not. Run it on a node in the datacenter that you’d like to test connectivity



Jens Rantil
Backend engineer
Tink AB

Phone: +46 708 84 18 32

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On Fri, Dec 19, 2014 at 11:16 AM, Alain RODRIGUEZ <>

> Hi guys,
> We expanded our cluster to a multiple DC configuration.
> Now I am wondering if there is any way to know:
> 1 - The replication lag between these 2 DC (Opscenter, nodetool, other ?)
> 2 - Make sure that sync is ok at any time
> I guess big companies running Cassandra are interested in these kind of
> info, so I think something exist but I am not aware of it.
> Any other important information or advice you can give me about best
> practices or tricks while running a multi DC (cross regions US <-> EU) is
> welcome of course !
> cheers,
> Alain
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