Changing keyspace replication strategy

Changing the strategy of a keyspace from SimpleStrategy to NetworkTopologyStrategy.

A keyspace is created with a strategy. For development work, the SimpleStrategy class is acceptable. For production work, the NetworkTopologyStrategy class must be set. To change the strategy, two steps are required. Altering the distribution of nodes within multiple datacenters when data is present should be accomplished by adding a datacenter, and then adding data to the new nodes in the new datacenter and removing nodes from the old datacenter.

Procedure

Change the snitch to a network-aware setting.
Alter the keyspace properties using the ALTER KEYSPACE command. For example, the keyspace cycling set to SimpleStrategy is switched to NetworkTopologyStrategy for a single datacenter DC1.
```
cqlsh> ALTER KEYSPACE cycling WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'DC1' : 3};
```
Note: Datacenter names are case sensitive. Verify the case of the using utility, such as nodetool status.
Alter the keyspace properties using the ALTER KEYSPACE command. For example, the keyspace cycling set to SimpleStrategy is switched to NetworkTopologyStrategy. Altering a keyspace to add a datacenter involves additional steps. Simply altering the keyspace may lead to faulty data replication. See switching snitches for additional information.
```
cqlsh> ALTER KEYSPACE cycling WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'DC1' : 3, 'DC2' : 2 };
```
Run nodetool-repair using the -full option on each node affected by the change. For details, see Updating the replication factor.
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), as in the following example:
```
cqlsh> ALTER KEYSPACE cycling WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'DC1' : 0, 'DC2' : 3, 'DC3' : 0 };
```