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.ran...@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.ran...@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 <arodr...@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 >> > >
