Schema¶

Keyspace¶

A ScyllaDB keyspace contains tables and defines settings for replication. To create a keyspace, use the following syntax:

CREATE KEYSPACE my_keyspace
  WITH replication = {
    'class': 'NetworkTopologyStrategy',
    'replication_factor': 3
};

Let’s break down the key concepts related to keyspace creation and replication in ScyllaDB.

Keyspace Creation

To create a keyspace, you use the CREATE KEYSPACE command followed by a keyspace name. In the example above, my_keyspace is the name of the keyspace you want to create.

Replication Strategy

Replication in ScyllaDB is the process of storing copies of data across multiple nodes to ensure fault tolerance and high availability. The replication strategy defines how data should be replicated across nodes in the cluster. In the example above, the replication strategy is set to NetworkTopologyStrategy.

This is a commonly used replication strategy in ScyllaDB, especially in production deployments. It allows you to specify the number of replicas for each datacenter separately, which provides fine-grained control over data distribution in a multi-datacenter environment. For example, if you have two datacenters, you can set different replication factors for each datacenter to handle data distribution and fault tolerance according to your specific requirements.

Replication Factor

The replication factor specifies how many copies (or replicas) of each piece of data should be stored in the cluster. In the example above, the replication factor is set to 3. This means that each piece of data will be replicated to three different nodes in the cluster.

The replication factor determines how many copies of your data exist across the cluster and directly affects fault tolerance and read performance.

Tables¶

Tables hold your data. Define them with specific column types and primary keys. Here’s how to create a table:

CREATE TABLE my_keyspace.users (
  user_id uuid PRIMARY KEY,
  first_name text,
  last_name text,
  age int
);

Let’s break down the components of this CREATE TABLE statement:

Keyspace

The users table is created within the my_keyspace keyspace. This means that the users table belongs to the my_keyspace keyspace, and all data stored in this table will be associated with that keyspace.

Table

The name of the table being created is users. This name should be unique within the keyspace.

Columns

Columns in ScyllaDB are defined within a table and have a specified data type. In the above users table, user_id, first_name, last_name, and age are columns which are further explained as follows:

• user_id: This is a column with the data type uuid. It is defined as the PRIMARY KEY. The primary key uniquely identifies each row in the table and is used for efficient data retrieval.

• first_name: This is a column with the data type text. It is used to store the user’s first name.

• last_name: This is another column with the data type text, used to store the user’s last name.

• age: This is a column with the data type int, used to store the user’s age.

In summary, the CREATE TABLE statement in ScyllaDB allows you to define the structure of your table, including column names, data types, and the primary key. This definition is essential for organizing and storing your data efficiently within the keyspace.

Primary Keys¶

The primary key can be made up of two parts: the partition key and optional clustering columns. The user_id column is the partition key in this example. It determines how data gets distributed across the cluster.

Additional columns, if present, can be specified as clustering columns, which determine the internal sorting of data within a partition.

CREATE TABLE my_keyspace.orders (
  order_id uuid,
  product_id uuid,
  quantity int,
  PRIMARY KEY (order_id, product_id)
);

In this example, order_id is the partition key, and product_id is the clustering key.

Partitions are determined by the partition key, a part of the primary key. Data is distributed across nodes based on the partition key. In the orders table, order_id determines the partition.

Learn More¶

• See Data Definition in the ScyllaDB documentation to learn more about defining a schema in ScyllaDB.