Alter Keyspace in Cassandra

In Cassandra, a keyspace is a namespace that defines data replication on nodes. To modify a keyspace after it has been created, we use the ALTER KEYSPACE command. The ALTER KEYSPACE command allows us to change the properties of a keyspace, such as replication factor and durable writes.

Syntax

The basic syntax for the ALTER KEYSPACE command is as follows:

ALTER KEYSPACE keyspace_name
  WITH replication = { 'class' : 'SimpleStrategy', 'replication_factor' : N }
  AND durable_writes = true|false;

Example

Suppose we have a keyspace called employees with a replication factor of 3. We want to change the replication factor to 4 and make durable writes disabled.

ALTER KEYSPACE employees
  WITH replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 4 }
  AND durable_writes = false;

Output

The output of the above command would be a success message confirming that the keyspace has been altered.

'employees' keyspace altered

Explanation

The ALTER KEYSPACE command modifies an existing keyspace in Cassandra. In the example above, we use the ALTER KEYSPACE command to modify the employees keyspace. We change the replication factor from 3 to 4 and disable durable writes.

The replication factor determines the number of copies of data stored on different nodes in a cluster. Increasing the replication factor can increase data durability but also increase network traffic. Durability writes option specifies whether a write should be considered successful only after it has been written to the disk of all replicas.

Use

We use the ALTER KEYSPACE command in Cassandra to modify the properties of an existing keyspace. This is useful when we need to change the replication factor to meet the changing needs of the application or disable durable writes for some operation to increase performance.

Important Points

• The ALTER KEYSPACE command can only be used to modify the properties that are listed in the WITH clause.
• Changing the replication factor can have a significant impact on performance due to increased network traffic.
• Disabling durable writes can improve write performance but increases risk of data loss.

Summary

In this tutorial, we learned how to use the ALTER KEYSPACE command in Cassandra to modify an existing keyspace. We saw the basic syntax of the ALTER KEYSPACE command and how to change the replication factor and durable writes settings. Altering a keyspace is useful in scenarios where we need to change the properties of a keyspace after its creation, such as when the replication factor needs to change to adapt to changing requirements.