Creating a keyspace

A keyspace is a collection of related tables, equivalent to a database in a relational system. To create the keyspace for our MyStatus application, issue the following statement in the CQL shell:

CREATE KEYSPACE "my_status"
WITH REPLICATION = {
  'class': 'SimpleStrategy', 'replication_factor': 1
};

Here we created a keyspace called my_status, which we will use for the remainder of this book. When we create a keyspace, we have to specify replication options. Cassandra provides several strategies for managing replication of data; SimpleStrategy is the best strategy as long as your Cassandra deployment does not span multiple data centers. The replication_factor value tells Cassandra how many copies of each piece of data are to be kept in the cluster; since we are only running a single instance of Cassandra, there is no point in keeping more than one copy of the data. In a production deployment, you would certainly want a higher replication factor; 3 is a good place to start.

Note

A few things at this point are worth noting about CQL's syntax:

• It's syntactically very similar to SQL; as we further explore CQL, the impression of similarity will not diminish.
• Double quotes are used for identifiers such as keyspace, table, and column names. As in SQL, quoting identifier names is usually optional, unless the identifier is a keyword or contains a space or another character that will trip up the parser.
• Single quotes are used for string literals; the key-value structure we use for replication is a map literal, which is syntactically similar to an object literal in JSON.
• As in SQL, CQL statements in the CQL shell must terminate with a semicolon.

Selecting a keyspace

Once you've created a keyspace, you would want to use it. In order to do this, employ the USE command:

USE "my_status";

This tells Cassandra that all future commands will implicitly refer to tables inside the my_status keyspace. If you close the CQL shell and reopen it, you'll need to reissue this command.