Keyspace Cassandra

A keyspace is a container that holds the column families, user defined types. In Cassandra, Keyspace is similar to schema RDBMS Database. Keyspace holds column families, indexes, user defined types, data center awareness, strategy used in keyspace, replication factor, etc.

Syntax

CREATE  KEYSPACE | SCHEMA  IF NOT EXISTS keyspace_name 
WITH REPLICATION = map
AND DURABLE_WRITES =  true | false 

• map is a JSON value

A map of properties and values defines the two different types of keyspaces:

{ 'class' : 'SimpleStrategy', 'replication_factor' : <integer> };
{ 'class' : 'NetworkTopologyStrategy'[, '<data center>' : <integer>, '<data center>' : <integer>] . . . };

Table of map values

Strategy: While declaring strategy name in Cassandra. There are two kinds of strategies declared in Cassandra Syntax.
1. Simple Strategy: Use only for a single data center. SimpleStrategy places the first replica on a node determined by the partitioner. Additional replicas are placed on the next nodes clockwise in the ring without considering topology (rack or data center location).
2. Network Topology Strategy:Use NetworkTopologyStrategy when you have (or plan to have) your cluster deployed across multiple data centers. This strategy specify how many replicas you want in each data center.

Durable Write (true or false)
You can set the DURABLE_WRITES option after the map specification of the CREATE KEYSPACE command. When set to false, data written to the keyspace bypasses the commit log. Be careful using this option because you risk losing data. Do not set this attribute on a keyspace using the SimpleStrategy.

Example execution creating keyspace in Cassandra database.
1. Creating Keyspace with SimpleStrategy

    cassandra@cqlsh> CREATE KEYSPACE app_putracode WITH REPLICATION = { 'class' : 'SimpleStrategy', 'replication_factor' : 3 };
    cassandra@cqlsh> describe keyspaces;
    system_schema  system         excelsior  system_distributed
    system_auth    app_putracode  keyspace1  system_traces

1. Creating Keyspace with NetworkTopologyStrategy
   For using NetworkTopologyStrategy in single server(for example). Check the datacenter name using nodetool.

   root@e465eeadc356:/# nodetool status;
   Datacenter: datacenter1
   =======================
   Status=Up/Down
   |/ State=Normal/Leaving/Joining/Moving
   --  Address     Load       Tokens       Owns (effective)  Host ID                               Rack
   UN  172.17.0.3  257.5 KiB  256          100.0%            1ae23679-8421-4e1d-8bc8-fe556631b916  rack1
   

   Cassandra uses datacenter1 as the default data center name. Create a keyspace named app_putracode_nts on a single node cluster, for example:

   CREATE KEYSPACE app_putracode_nts WITH REPLICATION = { 'class' : 'NetworkTopologyStrategy', 'datacenter1' : 1 };
   

   output

   root@e465eeadc356:/# cqlsh localhost -u cassandra -p cassandra
   Connected to Test Cluster at localhost:9042.
   [cqlsh 5.0.1 | Cassandra 3.11.1 | CQL spec 3.4.4 | Native protocol v4]
   Use HELP for help.
   cassandra@cqlsh> CREATE KEYSPACE app_putracode_nts WITH REPLICATION = { 'class' : 'NetworkTopologyStrategy', 'datacenter1' : 1 };
   cassandra@cqlsh> describe keyspaces;
   
   system_schema  app_putracode      keyspace1
   system_auth    excelsior          system_distributed
   system         app_putracode_nts  system_traces
   

Alter Keyspace / Schema Cassandra

Command Alter keyspace can change
1. Strategy
2. durable writes
3. replication

Syntax

ALTER  KEYSPACE | SCHEMA  keyspace_name
WITH REPLICATION = map
|  WITH DURABLE_WRITES =  true | false 
AND  DURABLE_WRITES =  true | false

example command

ALTER KEYSPACE app_putracode WITH REPLICATION={ 'class': 'NetworkTopologyStrategy', 'datacenter1':1};

Drop Keyspace / Schema Cassandra

Remove the keyspace and data.
Syntax

DROP  KEYSPACE | SCHEMA  IF EXISTS keyspace_name

example

cassandra@cqlsh> DROP KEYSPACE IF EXISTS app_putracode;
cassandra@cqlsh> DROP KEYSPACE IF EXISTS app_putracode;
cassandra@cqlsh> DROP KEYSPACE app_putracode;
ConfigurationException: Cannot drop non existing keyspace 'app_putracode'.
cassandra@cqlsh>

Using keyword if exists for checkking the keyspace first, if keyspace exists will be removed.