Changing keyspace replication strategy

A keyspace is created with a replication strategy. For development, the SimpleStrategy class is acceptable. For production, you must use NetworkTopologyStrategy. To change the strategy, alter the distribution of nodes within multiple datacenters by adding a datacenter, and then add data to the new nodes in the new datacenter and remove nodes from the old datacenter.

Procedure

  1. If necessary, change the snitch to a network-aware setting.

  2. Alter the keyspace properties using ALTER KEYSPACE:

    • Example 1: Switch the keyspace cycling from SimpleStrategy to NetworkTopologyStrategy for a single datacenter:

      ALTER KEYSPACE cycling WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'DC1' : 3};
    • Example 2: Switch the keyspace cycling from SimpleStrategy to NetworkTopologyStrategy for two datacenters:

      ALTER KEYSPACE cycling WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'DC1' : 3, 'DC2' : 2 };

      Simply altering the keyspace may lead to faulty data replication.

  3. Run nodetool repair using the -full option on each node affected by the change.

    nodetool repair -full <keyspace>

    Tarball path: <installation_location>/resources/cassandra/bin

    It is possible to restrict the replication of a keyspace to selected datacenters or a single datacenter. To do this, use the NetworkTopologyStrategy and set the replication factors of the excluded datacenters to 0 (zero):

    ALTER KEYSPACE cycling WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'DC1' : 0, 'DC2' : 3, 'DC3' : 0 };

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