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From Alain RODRIGUEZ <arodr...@gmail.com>
Subject Re: Multi DC informations (sync)
Date Fri, 19 Dec 2014 13:54:48 GMT
Hi Jens, thanks for your insight.

Replication lag in Cassandra terms is probably “Hinted handoff” --> Well I
think hinted handoff are only used when a node is down, and are not even
mandatory enabled. I guess that cross DC async replication is something
else, taht has nothing to see with hinted handoff, am I wrong ?

`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 from. --> Connectivity ≠ write success

Basically the two question can be changed this way:

1 - How to monitor the async cross dc write latency ?
2 - What error should I look for when async write fails (if any) ? Or is
there any other way to see that network throughput (for example) is too
small for a given traffic.

Hope this is clearer.

C*heers,

Alain

2014-12-19 11:44 GMT+01:00 Jens Rantil <jens.rantil@tink.se>:
>
> Alain,
>
> 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 from.
>
> Cheers,
> Jens
>
> ——— Jens Rantil Backend engineer Tink AB Email: jens.rantil@tink.se
> Phone: +46 708 84 18 32 Web: www.tink.se Facebook Linkedin Twitter
>
>
> On Fri, Dec 19, 2014 at 11:16 AM, Alain RODRIGUEZ <arodrime@gmail.com>
> wrote:
>
>> 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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