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cassandracql3cassandra-3.0

Insert rows only in one datacenter in cassandra cluster

For some test purposes I want to break a consistency of data in my test cassandra cluster, consisting of two datacenters.

I assumed that if I use a consistency level equal to LOCAL_QUORUM, or LOCAL_ONE I will achieve this. Let us say I have a cassandra node node11 belonging to DC1:

cqlsh node11
CONSISTENCY LOCAL_QUORUM;
INSERT INTO test.test (...) VALUES (...) ;

But in fact, data appears in all nodes. I can read it from the node22 belonging to the DC2 even with the consistency level LOCAL_*. I've double checked: the nodetool shows me the two datacenters and node11 certainly belongs to the DC1, while node22 belongs to the DC2.

My keyspace test is configured as follows:

CREATE KEYSPACE "test"
  WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'dc1' : 2, 'dc2' : 2};

and I have two nodes in each DC respectively.

My questions:

  1. It seems to me that I wrongly understand the idea of these consistency level. In fact they do not prevent from writing data to the different DC's, but just ask for appearing of the data at least in the current datacenter. Is it correct understanding?

  2. More essentially: is any way to perform such a trick and achieve such a "broken" consistency, when I have a different data stored in two datacenters within one cluster?

(At the moment I think that the only one way to achieve that - is to break the ring and do not allow nodes from one DC know anything about nodes from another DC, but I don't like this solution).

Solution
    1. LOCAL_QUORUM, this consistency level requires a quorum of acknoledgement received from the local DC but all the data are sent to all the nodes defined in the keyspace.

    Even at low consistency levels, the write is still sent to all replicas for the written key, even replicas in other data centers. The consistency level just determines how many replicas are required to respond that they received the write.

    https://docs.datastax.com/en/archived/cassandra/2.0/cassandra/dml/dml_config_consistency_c.html

    1. I don't think there is proper way to do that