The "ALTER keyspace" command is used to alter the replication factor, strategy name and durable writes properties in created keyspace in Cassandra.

Syntax:

1. ALTER KEYSPACE <identifier> WITH <properties>   

Or

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1. ALTER KEYSPACE "KeySpace Name"  
2. WITH replication = {'class': 'Strategy name', 'replication_factor' : 'No.Of  replicas'};   

Or

1. Alter Keyspace KeyspaceName with replication={'class':'StrategyName',   
2.     'replication_factor': no of replications on different nodes}   
3.         with DURABLE_WRITES=true/false   

Main points while altering Keyspace in Cassandra

• Keyspace Name: Keyspace name cannot be altered in Cassandra.
• Strategy Name: Strategy name can be altered by using a new strategy name.
• Replication Factor: Replication factor can be altered by using a new replication factor.
• DURABLE_WRITES: DURABLE_WRITES value can be altered by specifying its value true/false. By default, it is true. If set to false, no updates will be written to the commit log and vice versa.

Example:

Let's take an example to demonstrate "Alter Keyspace". This will alter the keyspace strategy from 'SimpleStrategy' to 'NetworkTopologyStrategy' and replication factor from 3 to 1 for DataCenter1.

1. ALTER KEYSPACE javatpoint  
2. WITH replication = {'class':'NetworkTopologyStrategy', 'replication_factor' : 1};