A keyspace in Cassandra is a namespace that defines data replication on nodes. A cluster contains one keyspace per node. Given below is the syntax for creating a keyspace using the statement CREATE KEYSPACE.

Syntax

CREATE KEYSPACE <identifier> WITH <properties>

i.e.

CREATE KEYSPACE “KeySpace Name”

WITH replication = {‘class’: ‘Strategy name’, ‘replication_factor’ : ‘No.Of replicas’};

CREATE KEYSPACE “KeySpace Name”

WITH replication = {‘class’: ‘Strategy name’, ‘replication_factor’ : ‘No.Of replicas’}

AND durable_writes = ‘Boolean value’;

The CREATE KEYSPACE statement has two properties: replication and durable_writes.

Replication

The replication option is to specify the Replica Placement strategy and the number of replicas wanted. The following table lists all the replica placement strategies.

Strategy name	Description
Simple Strategy’	Specifies a simple replication factor for the cluster.
Network Topology Strategy	Using this option, you can set the replication factor for each data-center independently.
Old Network Topology Strategy	This is a legacy replication strategy.

Using this option, you can instruct Cassandra whether to use commitlog for updates on the current KeySpace. This option is not mandatory and by default, it is set to true.

Example

Given below is an example of creating a KeySpace.

Here we are creating a KeySpace named Tecklearn.
We are using the first replica placement strategy, i.e.., Simple Strategy.
And we are choosing the replication factor to 1 replica.

cqlsh.> CREATE KEYSPACE tecklearn

WITH replication = {‘class’:’SimpleStrategy’, ‘replication_factor’ : 3};

Verification

You can verify whether the table is created or not using the command Describe. If you use this command over keyspaces, it will display all the keyspaces created as shown below.

cqlsh> DESCRIBE keyspaces;

tecklearn system system_traces

Here you can observe the newly created KeySpace tecklearn.

Durable_writes

By default, the durable_writes properties of a table is set to true, however it can be set to false. You cannot set this property to simplex strategy.

Example

Given below is the example demonstrating the usage of durable writes property.

cqlsh> CREATE KEYSPACE test

… WITH REPLICATION = { ‘class’ : ‘NetworkTopologyStrategy’, ‘datacenter1’ : 3 }

… AND DURABLE_WRITES = false;

Verification

You can verify whether the durable_writes property of test KeySpace was set to false by querying the System Keyspace. This query gives you all the KeySpaces along with their properties.

cqlsh> SELECT * FROM system_schema.keyspaces;

keyspace_name | durable_writes | strategy_class | strategy_options

—————-+—————-+——————————————————+—————————-

test | False | org.apache.cassandra.locator.NetworkTopologyStrategy | {“datacenter1” : “3”}

tecklearn | True | org.apache.cassandra.locator.SimpleStrategy | {“replication_factor” : “4”}

system | True | org.apache.cassandra.locator.LocalStrategy | { }

system_traces | True | org.apache.cassandra.locator.SimpleStrategy | {“replication_factor” : “2”}

(4 rows)

Here you can observe the durable_writes property of test KeySpace was set to false.

Using a Keyspace

You can use a created KeySpace using the keyword USE. Its syntax is as follows −

Syntax:USE <identifier>

Example

In the following example, we are using the KeySpace tecklearn.

cqlsh> USE tecklearn;

cqlsh:tecklearn>

Creating a Keyspace using Java API

You can create a Keyspace using the execute() method of Session class. Follow the steps given below to create a keyspace using Java API.

Step1: Create a Cluster Object

First of all, create an instance of Cluster.builder class of com.datastax.driver.core package as shown below.

//Creating Cluster.Builder object

Cluster.Builder builder1 = Cluster.builder();

Add a contact point (IP address of the node) using addContactPoint() method of Cluster.Builder object. This method returns Cluster.Builder.

//Adding contact point to the Cluster.Builder object

Cluster.Builder builder2 = build.addContactPoint( “127.0.0.1” );

Using the new builder object, create a cluster object. To do so, you have a method called build() in the Cluster.Builder class. The following code shows how to create a cluster object.

//Building a cluster

Cluster cluster = builder.build();

You can build a cluster object in a single line of code as shown below.

Cluster cluster = Cluster.builder().addContactPoint(“127.0.0.1”).build();

Step 2: Create a Session Object

Create an instance of Session object using the connect() method of Cluster class as shown below.

Session session = cluster.connect( );

This method creates a new session and initializes it. If you already have a keyspace, you can set it to the existing one by passing the keyspace name in string format to this method as shown below.

Session session = cluster.connect(“ Your keyspace name ” );

Step 3: Execute Query

You can execute CQL queries using the execute() method of Session class. Pass the query either in string format or as a Statement class object to the execute() method. Whatever you pass to this method in string format will be executed on the cqlsh.

In this example, we are creating a KeySpace named tp. We are using the first replica placement strategy, i.e., Simple Strategy, and we are choosing the replication factor to 1 replica.

You have to store the query in a string variable and pass it to the execute() method as shown below.

String query = “CREATE KEYSPACE tp WITH replication ”

+ “= {‘class’:’SimpleStrategy’, ‘replication_factor’:1}; “;

session.execute(query);

Step4 : Use the KeySpace

You can use a created KeySpace using the execute() method as shown below.

execute(“ USE tp ” );

Given below is the complete program to create and use a keyspace in Cassandra using Java API.

import com.datastax.driver.core.Cluster;

import com.datastax.driver.core.Session;

public class Create_KeySpace {

public static void main(String args[]){

//Query

String query = “CREATE KEYSPACE tp WITH replication ”

+ “= {‘class’:’SimpleStrategy’, ‘replication_factor’:1};”;

//creating Cluster object

Cluster cluster = Cluster.builder().addContactPoint(“127.0.0.1”).build();

//Creating Session object

Session session = cluster.connect();

//Executing the query

session.execute(query);

//using the KeySpace

session.execute(“USE tp”);

System.out.println(“Keyspace created”);

}

Save the above program with the class name followed by .java, browse to the location where it is saved. Compile and execute the program as shown below.

$javac Create_KeySpace.java

$java Create_KeySpace

Under normal conditions, it will produce the following output −

Keyspace created

Cassandra – Alter Keyspace

Altering a KeySpace

ALTER KEYSPACE can be used to alter properties such as the number of replicas and the durable_writes of a KeySpace. Given below is the syntax of this command.

Syntax

ALTER KEYSPACE <identifier> WITH <properties>

i.e.

ALTER KEYSPACE “KeySpace Name”

WITH replication = {‘class’: ‘Strategy name’, ‘replication_factor’ : ‘No.Of replicas’};

The properties of ALTER KEYSPACE are same as CREATE KEYSPACE. It has two properties: replication and durable_writes.

Replication

The replication option specifies the replica placement strategy and the number of replicas wanted.

Durable_writes

Using this option, you can instruct Cassandra whether to use commitlog for updates on the current KeySpace. This option is not mandatory and by default, it is set to true.

Example

Given below is an example of altering a KeySpace.

Here we are altering a KeySpace named Tecklearn.
We are changing the replication factor from 1 to 3.

cqlsh.> ALTER KEYSPACE tecklearn

WITH replication = {‘class’:’NetworkTopologyStrategy’, ‘replication_factor’ : 3};

Altering Durable_writes

You can also alter the durable_writes property of a KeySpace. Given below is the durable_writes property of the test KeySpace.

SELECT * FROM system_schema.keyspaces;

keyspace_name | durable_writes | strategy_class | strategy_options

—————-+—————-+——————————————————+—————————-

test | False | org.apache.cassandra.locator.NetworkTopologyStrategy | {“datacenter1″:”3”}

tecklearn | True | org.apache.cassandra.locator.SimpleStrategy | {“replication_factor”:”4″}

system | True | org.apache.cassandra.locator.LocalStrategy | { }

system_traces | True | org.apache.cassandra.locator.SimpleStrategy | {“replication_factor”:”2″}

(4 rows)

ALTER KEYSPACE test

WITH REPLICATION = {‘class’ : ‘NetworkTopologyStrategy’, ‘datacenter1’ : 3}

AND DURABLE_WRITES = true;

Once again, if you verify the properties of KeySpaces, it will produce the following output.

SELECT * FROM system_schema.keyspaces;

keyspace_name | durable_writes | strategy_class | strategy_options

—————-+—————-+——————————————————+—————————-

test | True | org.apache.cassandra.locator.NetworkTopologyStrategy | {“datacenter1″:”3”}

tecklearn | True | org.apache.cassandra.locator.SimpleStrategy | {“replication_factor”:”4″}

system | True | org.apache.cassandra.locator.LocalStrategy | { }

system_traces | True | org.apache.cassandra.locator.SimpleStrategy | {“replication_factor”:”2″}

(4 rows)

Altering a Keyspace using Java API

You can alter a keyspace using the execute() method of Session class. Follow the steps given below to alter a keyspace using Java API

Step1: Create a Cluster Object

First of all, create an instance of Cluster.builder class of com.datastax.driver.core package as shown below.

//Creating Cluster.Builder object

Cluster.Builder builder1 = Cluster.builder();

Add a contact point (IP address of the node) using the addContactPoint() method of Cluster.Builder object. This method returns Cluster.Builder.

//Adding contact point to the Cluster.Builder object

Cluster.Builder builder2 = build.addContactPoint( “127.0.0.1” );

Using the new builder object, create a cluster object. To do so, you have a method called build() in the Cluster.Builder class. The following code shows how to create a cluster object.

//Building a cluster

Cluster cluster = builder.build();

You can build the cluster object using a single line of code as shown below.

Cluster cluster = Cluster.builder().addContactPoint(“127.0.0.1”).build();

Step 2: Create a Session Object

Create an instance of Session object using the connect() method of Clusterclass as shown below.

Session session = cluster.connect( );

This method creates a new session and initializes it. If you already have a keyspace, you can set it to the existing one by passing the keyspace name in string format to this method as shown below.

Session session = cluster.connect(“ Your keyspace name ” );

Step 3: Execute Query

You can execute CQL queries using the execute() method of Session class. Pass the query either in string format or as a Statement class object to the execute() method. Whatever you pass to this method in string format will be executed on the cqlsh.

In this example,

We are altering a keyspace named tp. We are altering the replication option from Simple Strategy to Network Topology Strategy.
We are altering the durable_writes to false

You have to store the query in a string variable and pass it to the execute() method as shown below.

//Query

String query = “ALTER KEYSPACE tp WITH replication ” + “= {‘class’:’NetworkTopologyStrategy’, ‘datacenter1’:3}” +” AND DURABLE_WRITES = false;”;

session.execute(query);

Given below is the complete program to create and use a keyspace in Cassandra using Java API.

import com.datastax.driver.core.Cluster;

import com.datastax.driver.core.Session;

public class Alter_KeySpace {

public static void main(String args[]){

//Query

String query = “ALTER KEYSPACE tp WITH replication ” + “= {‘class’:’NetworkTopologyStrategy’, ‘datacenter1’:3}”

+ “AND DURABLE_WRITES = false;”;

//Creating Cluster object

Cluster cluster = Cluster.builder().addContactPoint(“127.0.0.1”).build();

//Creating Session object

Session session = cluster.connect();

//Executing the query

session.execute(query);

System.out.println(“Keyspace altered”);

}

Save the above program with the class name followed by .java, browse to the location where it is saved. Compile and execute the program as shown below.

$javac Alter_KeySpace.java

$java Alter_KeySpace

Under normal conditions, it produces the following output −

Keyspace Altered

Cassandra – Drop Keyspace

Dropping a Keyspace

You can drop a KeySpace using the command DROP KEYSPACE. Given below is the syntax for dropping a KeySpace.

Syntax

DROP KEYSPACE <identifier>

i.e.

DROP KEYSPACE “KeySpace name”

Example

The following code deletes the keyspace tecklearn.

cqlsh> DROP KEYSPACE tecklearn;

Verification

Verify the keyspaces using the command Describe and check whether the table is dropped as shown below.

cqlsh> DESCRIBE keyspaces;

system system_traces

Since we have deleted the keyspace tecklearn, you will not find it in the keyspaces list.

Dropping a Keyspace using Java API

You can create a keyspace using the execute() method of Session class. Follow the steps given below to drop a keyspace using Java API.

Step1: Create a Cluster Object

First of all, create an instance of Cluster.builder class of com.datastax.driver.core package as shown below.

//Creating Cluster.Builder object

Cluster.Builder builder1 = Cluster.builder();

Add a contact point (IP address of the node) using the addContactPoint() method of Cluster.Builder object. This method returns Cluster.Builder.

//Adding contact point to the Cluster.Builder object

Cluster.Builder builder2 = build.addContactPoint( “127.0.0.1” );

Using the new builder object, create a cluster object. To do so, you have a method called build() in the Cluster.Builder class. The following code shows how to create a cluster object.

//Building a cluster

Cluster cluster = builder.build();

You can build a cluster object using a single line of code as shown below.

Cluster cluster = Cluster.builder().addContactPoint(“127.0.0.1”).build();

Step 2: Create a Session Object

Create an instance of Session object using the connect() method of Cluster class as shown below.

Session session = cluster.connect( );

This method creates a new session and initializes it. If you already have a keyspace, you can set it to the existing one by passing the keyspace name in string format to this method as shown below.

Session session = cluster.connect(“ Your keyspace name”);

Step 3: Execute Query

You can execute CQL queries using the execute() method of Session class. Pass the query either in string format or as a Statement class object to the execute() method. Whatever you pass to this method in string format will be executed on the cqlsh.

In the following example, we are deleting a keyspace named tp. You have to store the query in a string variable and pass it to the execute() method as shown below.

String query = “DROP KEYSPACE tp; “;

session.execute(query);

Given below is the complete program to create and use a keyspace in Cassandra using Java API.

import com.datastax.driver.core.Cluster;

import com.datastax.driver.core.Session;

public class Drop_KeySpace {

public static void main(String args[]){

//Query

String query = “Drop KEYSPACE tp”;

//creating Cluster object

Cluster cluster = Cluster.builder().addContactPoint(“127.0.0.1”).build();

//Creating Session object

Session session = cluster.connect();

//Executing the query

session.execute(query);

System.out.println(“Keyspace deleted”);

}

Save the above program with the class name followed by .java, browse to the location where it is saved. Compile and execute the program as shown below.

$javac Delete_KeySpace.java

$java Delete_KeySpace

Under normal conditions, it should produce the following output −

Keyspace deleted

So, this brings us to the end of blog. This Tecklearn ‘How to create, alter and drop Keyspaces in Cassandra’ helps you with commonly asked questions if you are looking out for a job in Cassandra and No-SQL Database Domain.

If you wish to learn HBase and build a career in Cassandra or No-SQL Database domain, then check out our interactive, Apache Cassandra Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:

https://www.tecklearn.com/course/apache-cassandra-training/

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Rules of Cassandra data modelling
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