Configure an Amazon RDS SQL Server database

The following steps cover how to configure an Amazon RDS SQL Server database for use with Datastream:

Enable change data capture (CDC) for your source database. To enable CDC for your source database, connect to the database and run the following command at a SQL prompt, in a terminal, or using the Amazon RDS dashboard:
```
EXEC msdb.dbo.rds_cdc_enable_db 'DATABASE_NAME'
```
Replace DATABASE_NAME with the name of your source database.
Enable CDC on each table for which you need to capture changes:
```
USE [DATABASE_NAME]
EXEC sys.sp_cdc_enable_table
@source_schema = N'SCHEMA_NAME',
@source_name = N'TABLE_NAME',
@role_name = NULL
GO
```
Replace the following:
- DATABASE_NAME: the name of your source database
- SCHEMA_NAME: the name of the schema to which the tables belong
- TABLE_NAME: the name of the table for which you want to enable CDC
Start the SQL Server Agent and make sure it's running at all times. If the SQL Server Agent remains down for an extended period, the logs might get truncated, leading to a permanent loss of the change data that wasn't read by Datastream.

For information about running the SQL Server Agent, see Start, stop, or restart an instance of the SQL Server Agent.

Note: We recommend setting the automatic restart on for the SQL Server Agent service to prevent the agent from being down for a longer time.
Enable snapshot isolation.

When you backfill data from your SQL Server database, it's important to ensure consistent snapshots. If you don't apply the settings described in this section, changes made to the database during the backfill process might lead to duplicates or incorrect results, especially for tables without primary keys.

Enabling snapshot isolation creates a temporary view of your database at the start of the backfill process. This ensures that the data being copied remains consistent, even if other users are making changes to the live tables at the same time. Enabling snapshot isolation might have a slight performance impact, but it's essential for reliable data extraction.

To enable snapshot isolation:
1. Connect to your database using a SQL Server client.
2. Run the following command:
```
ALTER DATABASE DATABASE_NAME SET ALLOW_SNAPSHOT_ISOLATION ON;
```
Replace DATABASE_NAME with the name of you database.

Create a Datastream user:

Connect to the source database and enter the following command:
```
USE DATABASE_NAME;
```
Create a login to use while setting up the connection profile in Datastream.
```
CREATE LOGIN YOUR_LOGIN WITH PASSWORD = 'PASSWORD';
```

Create a user and assign the db_owner and db_denydatawriter roles to them:

CREATE USER USER_NAME FOR LOGIN YOUR_LOGIN;

EXEC sp_addrolemember 'db_owner', 'USER_NAME';
EXEC sp_addrolemember 'db_denydatawriter', 'USER_NAME';

Add this user to the master database:

USE master;
CREATE USER USER_NAME FOR LOGIN YOUR_LOGIN;

Additional steps required for the transaction logs CDC method

The steps described in this section are only required when you configure your source SQL Server database for use with the transaction logs CDC method.

Grant SELECT permissions for the sys.fn_dblog function.

USE master;
GRANT SELECT ON sys.fn_dblog TO USER_NAME;

Add your user to the msdb database and assign the following permissions to them:

USE msdb;
CREATE USER USER_NAME FOR LOGIN YOUR_LOGIN;
GRANT SELECT ON dbo.sysjobs TO USER_NAME;

Assign the following permissions to your user in the master database:
```
  USE master;
  GRANT VIEW SERVER STATE TO YOUR_LOGIN;
```
Set the retention period for which you want the changes to be available on your source.
```
USE [DATABASE_NAME]
EXEC sys.sp_cdc_change_job @job_type = 'capture' , @pollinginterval = 86399
EXEC sp_cdc_stop_job 'capture'
EXEC sp_cdc_start_job 'capture'
```
The @pollinginterval parameter is measured in seconds with a recommended value set to 86399. This means that the transaction log retains changes for 86,399 seconds (one day). Executing the sp_cdc_start_job 'capture procedure initiates the settings.

Set up a log truncation safeguard.

To make sure that the CDC reader has enough time to read the logs while allowing log truncation to prevent using up the storage space, you can set up a log truncation safeguard:

Connect to the database using a SQL Server client.

Create a dummy table in the database:

USE [DATABASE_NAME];
CREATE TABLE dbo.gcp_datastream_truncation_safeguard (
  [id] INT IDENTITY(1,1) PRIMARY KEY,
  CreatedDate DATETIME DEFAULT GETDATE(),
  [char_column] CHAR(8)
  );

Create a stored procedure that runs an active transaction for a period that you specify to prevent log truncation:

CREATE PROCEDURE [dbo].[DatastreamLogTruncationSafeguard] @transaction_logs_retention_time INT
AS
BEGIN
  -- Start a new transaction
  BEGIN TRANSACTION;
  INSERT INTO dbo.gcp_datastream_truncation_safeguard (char_column) VALUES ('a')

DECLARE @formatted_time VARCHAR(5)
SET @formatted_time = CONVERT(VARCHAR(5), DATEADD(MINUTE, @transaction_logs_retention_time, 0), 108);
  -- Wait for X minutes before ending the transaction
  WAITFOR DELAY @formatted_time;
  -- Commit the transaction
  COMMIT TRANSACTION;
END;

Create another stored procedure. This time, you create a job that runs the stored procedure that you created in the previous step according to a specified cadence:

CREATE PROCEDURE [dbo].[SetUpDatastreamJob] @transaction_logs_retention_time INT
AS
BEGIN
  DECLARE @database_name VARCHAR(MAX)
  SET @database_name =  (SELECT DB_NAME());;

  DECLARE @command_str VARCHAR(MAX);
  SET @command_str = CONCAT('Use ', @database_name,'; exec dbo.DatastreamLogTruncationSafeguard @transaction_logs_retention_time = ' + @transaction_logs_retention_time)

  DECLARE @job_name VARCHAR(MAX);
SET @job_name =
  CONCAT(@database_name, '_', 'DatastreamLogTruncationSafeguardJob1')

    -- Add 3 schedules to the job to run again after specified time.
    IF
      NOT EXISTS(
        SELECT *
        FROM msdb.dbo.sysjobs
        WHERE name = @job_name
      )
        BEGIN
          EXEC
            msdb.dbo.sp_add_job
              @job_name
  = @job_name,
  @enabled = 1,
  @description = N'Execute the procedure to run an active transaction for x minutes.';

EXEC msdb.dbo.sp_add_jobstep @job_name = @job_name,
@step_name = N'Execute_DatastreamLogTruncationSafeguard',
@subsystem = N'TSQL',
@command = @command_str;

  -- Add a schedule that runs the stored procedure every given minutes starting now.
  DECLARE @schedule_name_1 VARCHAR(MAX);
  SET @schedule_name_1 = CONCAT(@database_name, '_', 'DatastreamEveryGivenMinutesFromNow')

  DECLARE @start_time_1 time;
  SET @start_time_1 = DATEADD(SECOND, 1, GETDATE());
  DECLARE @formatted_start_time_1 INT;
  SET @formatted_start_time_1 = CONVERT(INT, REPLACE(CONVERT(VARCHAR(8), @start_time_1, 114), ':' ,''));

  EXEC msdb.dbo.sp_add_schedule
  @schedule_name = @schedule_name_1,
  @freq_type = 4,  -- daily start
  @freq_subday_type = 4,  -- every X minutes daily
  @freq_interval = 1,
  @freq_subday_interval = @transaction_logs_retention_time,
  @active_start_time = @formatted_start_time_1;

  EXEC msdb.dbo.sp_attach_schedule
  @job_name = @job_name,
  @schedule_name = @schedule_name_1 ;

  -- Add a schedule that runs the stored procedure after every given minutes starting after some delay.
  DECLARE @schedule_name_2 VARCHAR(MAX);
  Set @schedule_name_2 = CONCAT(@database_name, '_', 'DatastreamEveryGivenMinutesAfterDelay');

  DECLARE @start_time_2 time;
  SET @start_time_2 = DATEADD(MINUTE, @transaction_logs_retention_time / 2, GETDATE());

  DECLARE @formatted_start_time_2 INT;
  SET @formatted_start_time_2 = CONVERT(INT, REPLACE(CONVERT(VARCHAR(8), @start_time_2, 114), ':' ,''));

  EXEC msdb.dbo.sp_add_schedule
  @schedule_name = @schedule_name_2,
  @freq_type = 4,  -- daily start
  @freq_subday_type = 4,  -- every x minutes daily
  @freq_interval = 1,
  @freq_subday_interval = @transaction_logs_retention_time,
  @active_start_time = @formatted_start_time_2;

  EXEC msdb.dbo.sp_attach_schedule
  @job_name = @job_name,
  @schedule_name = @schedule_name_2 ;

  -- Add a schedule that runs the stored procedure on the SQL Server Agent startup.
  DECLARE @schedule_name_agent_startup VARCHAR(MAX);
  Set @schedule_name_agent_startup = CONCAT(@database_name, '_', 'DatastreamSqlServerAgentStartupSchedule')

  EXEC msdb.dbo.sp_add_schedule
  @schedule_name = @schedule_name_agent_startup,
  @freq_type = 64,  -- start on SQL Server Agent startup
  @active_start_time = @formatted_start_time_1;

  EXEC msdb.dbo.sp_attach_schedule
  @job_name = @job_name,
  @schedule_name = @schedule_name_agent_startup ;

  EXEC msdb.dbo.sp_add_jobserver
  @job_name = @job_name,
  @server_name = @@servername ;
  END
END;

Execute the stored procedure that creates the Datastream job.
```
EXEC dbo.SetUpDatastreamJob @@transaction_logs_retention_time = (INT)
```
Replace INT with the number of minutes for which you want to retain the logs. For example:
- The value of 60 sets the retention time to 1 hour
- The value of 24 * 60 sets the retention time to 1 day
- The value of 3 * 24 * 60 sets the retention time to 3 days