How to connect PolyBase to AlloyDB

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 AlloyDB, you get access to your AlloyDB data directly alongside your SQL Server data. This article describes creating an external data source and external tables to grant access to live AlloyDB 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 AlloyDB data using PolyBase due to optimized data processing built into the driver. When you issue complex SQL queries from SQL Server to AlloyDB, the driver pushes down supported SQL operations, like filters and aggregations, directly to AlloyDB 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 AlloyDB data, using a single query to pull data from distributed sources.

Connect to AlloyDB

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 AlloyDB Sys is created automatically).

The following connection properties are usually required in order to connect to AlloyDB.

• Server: The host name or IP of the server hosting the AlloyDB database.
• User: The user which will be used to authenticate with the AlloyDB server.
• Password: The password which will be used to authenticate with the AlloyDB server.

You can also optionally set the following:

• Database: The database to connect to when connecting to the AlloyDB Server. If this is not set, the user's default database will be used.
• Port: The port of the server hosting the AlloyDB database. This property is set to 5432 by default.

Authenticating with Standard Authentication

Standard authentication (using the user/password combination supplied earlier) is the default form of authentication.

No further action is required to leverage Standard Authentication to connect.

Authenticating with pg_hba.conf Auth Schemes

There are additional methods of authentication available which must be enabled in the pg_hba.conf file on the AlloyDB server.

Find instructions about authentication setup on the AlloyDB Server here.

Authenticating with MD5 Authentication

This authentication method must be enabled by setting the auth-method in the pg_hba.conf file to md5.

Authenticating with SASL Authentication

This authentication method must be enabled by setting the auth-method in the pg_hba.conf file to scram-sha-256.

Authenticating with Kerberos

The authentication with Kerberos is initiated by AlloyDB Server when the ∏ is trying to connect to it. You should set up Kerberos on the AlloyDB Server to activate this authentication method. Once you have Kerberos authentication set up on the AlloyDB Server, see the Kerberos section of the help documentation for details on how to authenticate with Kerberos.

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

Create an External Data Source for AlloyDB 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 AlloyDB data.

NOTE: IDENTITY and SECRET correspond with the User and Password properties for AlloyDB.

CREATE DATABASE SCOPED CREDENTIAL alloydb_creds
WITH IDENTITY = 'alloydb_username', SECRET = 'alloydb_password';

Create an External Data Source for AlloyDB

Execute a CREATE EXTERNAL DATA SOURCE SQL command to create an external data source for AlloyDB 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 AlloyDB. PUSHDOWN is set to ON by default, meaning the ODBC Driver can leverage server-side processing for complex queries.

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

Create External Tables for AlloyDB

After creating the external data source, use CREATE EXTERNAL TABLE statements to link to AlloyDB data from your SQL Server instance. The table column definitions must match those exposed by the CData ODBC Driver for AlloyDB. 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 AlloyDB Orders would look similar to the following:

CREATE EXTERNAL TABLE Orders(
  ShipName [nvarchar](255) NULL,
  ShipCity [nvarchar](255) NULL,
  ...
) WITH ( 
  LOCATION='Orders',
  DATA_SOURCE=cdata_alloydb_source
);

Having created external tables for AlloyDB 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 AlloyDB, freeing up local resources and computing power. Download a free, 30-day trial of the ODBC Driver for AlloyDB and start working with live AlloyDB data alongside your SQL Server data today.