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From Konstantin Naryshkin <>
Subject Re: questions on frequency and timing of async replication between DCs
Date Mon, 14 Nov 2011 14:39:54 GMT
It may be the case that your CL is the issue. You are writing it at
ONE, which means that out of the 4 replicas of that key (two in each
data center), you are only putting it on one of them. When you read at
CL ONE, if only looks at a single replica to see if the data is there.
In other words. If your read and your write do not select the same
node to look at, there is no guarantee that any successfully written
data is going to be there. The rule is, in order to be able to access
data properly, CL.READ + CL.WRITE > RF. Your RF is 4 while your CL are
both 1.

On Fri, Nov 11, 2011 at 18:35, Subrahmanya Harve
<> wrote:
> If i query by list command, i do see the data i am looking for.
> Interestingly, if do list on each of the nodes using cli, i get back a
> different number of rows!
> i did not want to query by ALL because of 2 reasons - 1. It might take too
> long to return. 2 it might not return me anything just because a node was
> temporarily down?
> any idea whats going on here?
> i am also wondering if anyone has gone to production with cross-dc using
> 0.8.7 and how its working out? lessons learnt, etc
> On Fri, Nov 11, 2011 at 2:55 PM, Jeremiah Jordan
> <> wrote:
>> If you query with ALL do you get the data?  If you query with a range
>> slice do you get the data (list from the cli)?
>> On 11/11/2011 04:10 PM, Subrahmanya Harve wrote:
>>> I have cross dc replication set up using 0.8.7 with 3 nodes on each DC by
>>> following the +1 rule for tokens.
>>> I am seeing an issue where the insert into a DC happened successfully but
>>> on querying from cli or through Hector, i am not seeing the data being
>>> returned. i used cli on every node of both DCs and every node returned
>>> blank. So basic question is where is my data? CL.WRITE=ONE, CL.READ=1. RF =
>>> DC:2, DC:2
>>> Apart from checking the data directory size on each DC to verify that
>>> cross-dc replication has happened, what others steps can i take to verify
>>> that cross dc replication is happening successfully? What tuning params can
>>> i control with regard to cross-dc replication? (frequency? batch size?, etc)
>>> would greatly appreciate any help.

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