Cassandra - Create Keyspace

Creating a Keyspace using Cqlsh

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.

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 Howcodex.

• 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 howcodex
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;

howcodex system system_traces 

Here you can observe the newly created KeySpace howcodex.

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"}

 howcodex |           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 howcodex.

cqlsh> USE howcodex;
cqlsh:howcodex>

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