Alter Keyspace in Cassandra

In Cassandra, a keyspace is the outermost container for data. It is similar to a database in a traditional RDBMS. A keyspace holds tables, and it is defined as a namespace that defines the replication strategy and other settings for the tables within it. The keyspace defines how data is distributed across nodes in a Cassandra cluster. In this tutorial, we will learn how to alter an existing keyspace in Cassandra.

Syntax

The syntax to alter a keyspace in Cassandra is as follows:

ALTER KEYSPACE <keyspace_name>
  WITH [replication = { 'class' : <class_name>, <option1> : <value1>, ... }]
  [AND DURABLE_WRITES = (true|false)];

Where:

• keyspace_name: the name of the keyspace to be altered
• class_name: the replication class name
• option1: value1: the options and values for the replication strategy
• DURABLE_WRITES: true or false to enable/disable durable writes for the keyspace

Components

Let’s discuss the various components of the syntax:

• ALTER KEYSPACE: the ALTER KEYSPACE statement is used to modify an existing keyspace.
• <keyspace_name>: the name of the keyspace to be altered.
• WITH: used to add options to the ALTER KEYSPACE statement.
• replication: the replication factor options are specified using the replication keyword, followed by a set of options specified in JSON format.
• class: the name of the replication class to be used.
• option1: value1: the options and values for the replication strategy. These can be different for different replication classes.
• AND DURABLE_WRITES: specifies if durable writes should be enabled or disabled for the keyspace.

Examples

Let’s look at some examples of altering a keyspace in Cassandra:

Example 1: Altering a keyspace to change the replication factor

ALTER KEYSPACE DeveloperPublish WITH replication = {'class': 'SimpleStrategy', 'replication_factor': 3};

In this example, we are altering the DeveloperPublish keyspace to use the SimpleStrategy replication strategy with a replication factor of 3. This means that each data item will be replicated to three nodes. You can also use the NetworkTopologyStrategy replication strategy to spread replicas across multiple data centers.

Example 2: Altering a keyspace to change the durable writes setting

ALTER KEYSPACE DeveloperPublish WITH durable_writes = false;

In this example, we are altering the DeveloperPublish keyspace to turn off durable writes. This means that Cassandra will not write to the commit log, which can result in improved write performance but reduced durability.

Example 3: Altering a keyspace to add a new replication data center

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

In this example, we are altering the DeveloperPublish keyspace to use the NetworkTopologyStrategy replication strategy and add a new replication data center named DC2 with a replication factor of 2. This means that each data item will be replicated to three nodes in data center DC1 and two nodes in data center DC2.

Example 4: Altering a keyspace to change the compression settings

ALTER KEYSPACE DeveloperPublish WITH compression = {'sstable_compression': 'SnappyCompressor', 'chunk_length_kb': 64};

In this example, we are altering the DeveloperPublish keyspace to use the SnappyCompressor compression algorithm with a chunk length of 64 KB. This can help to reduce the size of stored data and improve read performance.

In conclusion, altering a keyspace in Cassandra is a simple process that can be done using the ALTER KEYSPACE command. You can change various properties of a keyspace such as the replication factor, durable writes setting, replication data centers, and compression settings. By understanding how to alter a keyspace, you can easily modify your Cassandra database to meet your changing application requirements.