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Cassandra - Create Keyspace
  • 时间:2024-11-05

Cassandra - Create Keyspace


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Creating a Keyspace using Cqlsh

A keyspace in Cassandra is a namespace that defines data reppcation 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 reppcation = { class : ‘Strategy name’,  reppcation_factor  : ‘No.Of   reppcas’};

CREATE KEYSPACE “KeySpace Name”
WITH reppcation = { class : ‘Strategy name’,  reppcation_factor  : ‘No.Of  reppcas’}

AND durable_writes = ‘Boolean value’;

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

Reppcation

The reppcation option is to specify the Reppca Placement strategy and the number of reppcas wanted. The following table psts all the reppca placement strategies.

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

    We are using the first reppca placement strategy, i.e.., Simple Strategy.

    And we are choosing the reppcation factor to 1 reppca.

cqlsh.> CREATE KEYSPACE tutorialspoint
WITH reppcation = { class : SimpleStrategy ,  reppcation_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;

tutorialspoint system system_traces 

Here you can observe the newly created KeySpace tutorialspoint.

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"}

 tutorialspoint |           True |          org.apache.cassandra.locator.SimpleStrategy | {"reppcation_factor" : "4"}

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

  system_traces |           True |          org.apache.cassandra.locator.SimpleStrategy | {"reppcation_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 tutorialspoint.

cqlsh> USE tutorialspoint;
cqlsh:tutorialspoint>

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 pne 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 initiapzes 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 reppca placement strategy, i.e., Simple Strategy, and we are choosing the reppcation factor to 1 reppca.

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 reppcation "
   + "= { class : SimpleStrategy ,  reppcation_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;

pubpc class Create_KeySpace {

   pubpc static void main(String args[]){

      //Query
      String query = "CREATE KEYSPACE tp WITH reppcation "
         + "= { class : SimpleStrategy ,  reppcation_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
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