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From Maifi Khan <>
Subject questions regarding read and write in cassandra
Date Thu, 19 Aug 2010 17:00:47 GMT
I have a question in the following scenario.
Say we have 10 nodes, Replication factor is 5.
Now, say, for Row X, Column Y, data is replicated to node 1,2,3,4,5
and current value is 10
Say, I issue a write command with value “20” to Row X, column Y with
quorum(n/2+1=3 nodes).  Say it updated 1 and 2 and failed to update
any other node. So it failed to write to 3 nodes. What happens in such

Q: Will the user returned failed?

Now, assuming that the write failed.
What value will I see if I want to read the same cell with Quorum?
Now, say I read the data with quorum. It read from 1, 4, 5 and see
that node 1 has the most recent data (“20” which is still there as
cassandra does not roll back).
Will it will return the data “20” to the user or will it return the
earlier value 10 as it is returned by the node 4 and 5?

Also, does read repair tries to propagate 20 to all the replicas
although cassandra returned failed to the user?


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