How to connect PolyBase to Cassandra

PolyBase for SQL Server allows you to query external data by using the same Transact-SQL syntax used to query a database table. When paired with the CData ODBC Driver for Apache Cassandra, you get access to your Cassandra data directly alongside your SQL Server data. This article describes creating an external data source and external tables to grant access to live Cassandra data using T-SQL queries.

NOTE: PolyBase is only available on SQL Server 19 and above, and only for Standard SQL Server.

The CData ODBC drivers offer unmatched performance for interacting with live Cassandra data using PolyBase due to optimized data processing built into the driver. When you issue complex SQL queries from SQL Server to Cassandra, the driver pushes down supported SQL operations, like filters and aggregations, directly to Cassandra and utilizes the embedded SQL engine to process unsupported operations (often SQL functions and JOIN operations) client-side. And with PolyBase, you can also join SQL Server data with Cassandra data, using a single query to pull data from distributed sources.

Connect to Cassandra

If you have not already, first specify connection properties in an ODBC DSN (data source name). This is the last step of the driver installation. You can use the Microsoft ODBC Data Source Administrator to create and configure ODBC DSNs. To create an external data source in SQL Server using PolyBase, configure a System DSN (CData Cassandra Sys is created automatically).

Set the Server, Port, and Database connection properties to connect to Cassandra. Additionally, to use internal authentication set the User and Password connection properties.

Click "Test Connection" to ensure that the DSN is connected to Cassandra properly. Navigate to the Tables tab to review the table definitions for Cassandra.

Create an External Data Source for Cassandra Data

After configuring the connection, you need to create a master encryption key and a credential database for the external data source.

Creating a Master Encryption Key

Execute the following SQL command to create a new master key, 'ENCRYPTION,' to encrypt the credentials for the external data source.

CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'password';

Creating a Credential Database

Execute the following SQL command to create credentials for the external data source connected to Cassandra data.

NOTE: Since Cassandra does not require a User or Password to authenticate, you may use whatever values you wish for IDENTITY and SECRET.

CREATE DATABASE SCOPED CREDENTIAL cassandra_creds
WITH IDENTITY = 'username', SECRET = 'password';

Create an External Data Source for Cassandra

Execute a CREATE EXTERNAL DATA SOURCE SQL command to create an external data source for Cassandra with PolyBase:

• Set the LOCATION parameter , using the DSN and credentials configured earlier.

NOTE: SERVERNAME and PORT corresponds to the Server and Port connection properties for Cassandra. PUSHDOWN is set to ON by default, meaning the ODBC Driver can leverage server-side processing for complex queries.

CREATE EXTERNAL DATA SOURCE cdata_cassandra_source
WITH ( 
  LOCATION = 'odbc://SERVERNAME[:PORT]',
  CONNECTION_OPTIONS = 'DSN=CData Cassandra Sys',
  -- PUSHDOWN = ON | OFF,
  CREDENTIAL = cassandra_creds
);

Create External Tables for Cassandra

After creating the external data source, use CREATE EXTERNAL TABLE statements to link to Cassandra data from your SQL Server instance. The table column definitions must match those exposed by the CData ODBC Driver for Apache Cassandra. You can refer to the Tables tab of the DSN Configuration Wizard to see the table definition.

Sample CREATE TABLE Statement

The statement to create an external table based on a Cassandra Customer would look similar to the following:

CREATE EXTERNAL TABLE Customer(
  City [nvarchar](255) NULL,
  TotalDue [nvarchar](255) NULL,
  ...
) WITH ( 
  LOCATION='Customer',
  DATA_SOURCE=cdata_cassandra_source
);

Having created external tables for Cassandra in your SQL Server instance, you are now able to query local and remote data simultaneously. Thanks to built-in query processing in the CData ODBC Driver, you know that as much query processing as possible is being pushed to Cassandra, freeing up local resources and computing power. Download a free, 30-day trial of the ODBC Driver for Cassandra and start working with live Cassandra data alongside your SQL Server data today.