Configure a self-managed SQL Server database for CDC

This page describes how to configure change data capture (CDC) to stream data from a self-managed SQL Server database to a supported destination, such as BigQuery or Cloud Storage.

Ensure your database is using the full recovery model. To check and set the recovery model, connect to the database and run the following command at a SQL prompt or in a terminal:
```
USEmaster
GO
ALTERDATABASE[DATABASE_NAME]SETRECOVERYFULL
GO
```
Replace DATABASE_NAME with the name of your source database.

Note: After setting the recovery model to FULL, the database remains in a pseudo-simple recovery state until you take a full database backup. You must perform a full database backup before the transaction log begins retaining records for change data capture.
Enable CDC for your source database. To do it, connect to the database and run the following command at a SQL prompt or in a terminal:
```
USE[DATABASE_NAME]
GO
EXECsys.sp_cdc_enable_db
GO
```
Replace DATABASE_NAME with the name of your source database.
Enable CDC on the tables for which you need to capture changes:
```
USE[DATABASE_NAME]
EXECsys.sp_cdc_enable_table
@source_schema=N'SCHEMA_NAME',
@source_name=N'TABLE_NAME',
@role_name=NULL
GO
```
Note: You need to run the command for each table for which you want to enable CDC.

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. Applying snapshot isolation settings is required if your stream includes 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:
```
ALTERDATABASEDATABASE_NAMESETALLOW_SNAPSHOT_ISOLATIONON;
```
Replace DATABASE_NAME with the name of you database.
Create a Datastream user:
1. Connect to the source database and enter the following command:
```
USEDATABASE_NAME;
```
2. Create a login to use while setting up the connection profile in Datastream.
```
CREATELOGINYOUR_LOGINWITHPASSWORD='PASSWORD';
```
3. Create a user:
```
CREATEUSERUSER_NAMEFORLOGINYOUR_LOGIN;
```
4. Assign the db_datareader role to them:
```
EXECsp_addrolemember'db_datareader','USER_NAME';
```
5. Grant the VIEW DATABASE STATE permission to them:
```
GRANTVIEWDATABASESTATETOUSER_NAME;
```
6. Add this user to the master database:
```
USEmaster;
CREATEUSERUSER_NAMEFORLOGINYOUR_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.

Connect to the source database and assign the db_owner and db_denydatawriter roles to your user:

USEDATABASE_NAME;
EXECsp_addrolemember'db_owner','USER_NAME';
EXECsp_addrolemember'db_denydatawriter','USER_NAME';

Grant SELECT permissions for the sys.fn_dblog function.

USEmaster;
GRANTSELECTONsys.fn_dblogTOUSER_NAME;

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

USEmsdb;
CREATEUSERUSER_NAMEFORLOGINYOUR_LOGIN;
GRANTSELECTONdbo.sysjobsTOUSER_NAME;

Assign the following permissions to your user in the master database:
```
USEmaster;
GRANTVIEWSERVERSTATETOYOUR_LOGIN;
```
Set the polling interval for which you want the changes to be available on your source.
```
USE[DATABASE_NAME]
EXECsys.sp_cdc_change_job@job_type='capture',@pollinginterval=86399
EXECsp_cdc_stop_job'capture'
EXECsp_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.
If there are any cleanup or capture jobs running on your database, stop them. For more information, see Administer and monitor change data capture.

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

CREATEPROCEDUREdbo.DatastreamLogTruncationSafeguard@transaction_logs_retention_timeINT
AS
BEGIN
DECLARE@transactionLogTABLE(beginLSNBINARY(10),endLSNBINARY(10))
INSERT@transactionLogEXECsp_repltrans
DECLARE@currentDateTimeDATETIME=GETDATE()
DECLARE@cutoffDateTimeDATETIME=DATEADD(MINUTE,-@transaction_logs_retention_time,@currentDateTime)
DECLARE@firstValidLSNBINARY(10)=NULL
DECLARE@lastValidLSNBINARY(10)=NULL
DECLARE@firstTxnTimeDATETIME=NULL
DECLARE@lastTxnTimeDATETIME=NULL
SELECTTOP1
@lastTxnTime=t.logStartTime,
@lastValidLSN=t.beginLSN
FROM(
SELECT
beginLSNASbeginLSN,
(SELECTTOP1[begin time]
FROMfn_dblog(stuff(stuff(CONVERT(CHAR(24),beginLSN,1),19,0,':'),11,0,':'),DEFAULT))ASlogStartTime
FROM@transactionLog
)t
ORDERBYt.beginLSNDESC
-- If all transactions are before cutoff, clear everything
IF(@lastTxnTime < @cutoffDateTime)
BEGIN
EXECsp_repldoneNULL,NULL,0,0,1
END
ELSE
BEGIN
-- Find the earliest transaction
SELECTTOP1
@firstTxnTime=t.logStartTime,
@firstValidLSN=ISNULL(@firstValidLSN,t.beginLSN)
FROM(
SELECT
beginLSNASbeginLSN,
(SELECTTOP1[begin time]
FROMfn_dblog(stuff(stuff(CONVERT(CHAR(24),beginLSN,1),19,0,':'),11,0,':'),DEFAULT))ASlogStartTime
FROM@transactionLog
)t
ORDERBYt.beginLSNASC
IF(@firstTxnTime < @cutoffDateTime)
BEGIN
-- Identify the earliest and latest LSNs within VLogs before cutoff
SELECT
@firstValidLSN=SUBSTRING(MAX(t.lsnMarkers),1,10),
@lastValidLSN=SUBSTRING(MAX(t.lsnMarkers),11,10)
FROM(
SELECTMIN(beginLSN+endLSN)ASlsnMarkers
FROM@transactionLog
GROUPBYSUBSTRING(beginLSN,1,4)
)t
WHERE(
SELECTTOP1[begin time]
FROMfn_dblog(stuff(stuff(CONVERT(CHAR(24),t.lsnMarkers,1),19,0,':'),11,0,':'),DEFAULT)
WHEREOperation='LOP_BEGIN_XACT'
) < @cutoffDateTime
EXECsp_repldone@firstValidLSN,@lastValidLSN,0,0,0
END
END
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:

CREATEPROCEDURE[dbo].[SetUpDatastreamJob]@transaction_logs_retention_timeINT
AS
BEGIN
DECLARE@database_nameVARCHAR(MAX)
SET@database_name=(SELECTDB_NAME());;
DECLARE@command_strVARCHAR(MAX);
SET@command_str=CONCAT('Use ',@database_name,'; exec dbo.DatastreamLogTruncationSafeguard @transaction_logs_retention_time = '+CAST(@transaction_logs_retention_timeASVARCHAR(10)));
DECLARE@job_nameVARCHAR(MAX);
SET@job_name=
CONCAT(@database_name,'_','DatastreamLogTruncationSafeguardJob1')
DECLARE@current_timeINT
=CAST(FORMAT(GETDATE(),'HHmmss')ASINT);
-- Schedule the procedure to run after every 5 minutes.
IFNOTEXISTS(
SELECT*FROMmsdb.dbo.sysjobs
WHEREname=@job_name
)
BEGIN
EXECmsdb.dbo.sp_add_job
@job_name=@job_name,
@enabled=1,
@description=N'Execute the procedure every 5 minutes.';
EXECmsdb.dbo.sp_add_jobstep
@job_name=@job_name,
@step_name=N'Execute_DatastreamLogTruncationSafeguard',
@subsystem=N'TSQL',
@command=@command_str;
DECLARE@schedule_name_1VARCHAR(MAX);
SET@schedule_name_1=CONCAT(@database_name,'_','DatastreamEveryFiveMinutesSchedule')
EXECmsdb.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=5,
@active_start_time=@current_time;
EXECmsdb.dbo.sp_attach_schedule
@job_name=@job_name,
@schedule_name=@schedule_name_1;
-- Add a schedule that runs the stored procedure on the SQL Server Agent startup.
DECLARE@schedule_name_agent_startupVARCHAR(MAX);
SET@schedule_name_agent_startup=CONCAT(@database_name,'_','DatastreamSqlServerAgentStartupSchedule')
EXECmsdb.dbo.sp_add_schedule
@schedule_name=@schedule_name_agent_startup,
@freq_type=64,-- start on SQL Server Agent startup
@active_start_time=@current_time;
EXECmsdb.dbo.sp_attach_schedule
@job_name=@job_name,
@schedule_name=@schedule_name_agent_startup;
EXECmsdb.dbo.sp_add_jobserver
@job_name=@job_name,
@server_name=@@servername;
END
END;

Execute the stored procedure that creates the Datastream job.
```
DECLARE@transaction_logs_retention_timeINT=(INT)
EXEC[dbo].[SetUpDatastreamJob]@transaction_logs_retention_time
```
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

What's next

Learn more about how Datastream works with SQL Server sources.

Configure a self-managed SQL Server database for CDC Stay organized with collections Save and categorize content based on your preferences.

Additional steps required for the transaction logs CDC method

What's next

Configure a self-managed SQL Server database for CDC