Prepare SQL Server for RDI

Prepare SQL Server databases to work with RDI

To prepare your SQL Server database for Debezium, you must first run a query to enable CDC globally and then separately enable CDC for each table you want to capture. You need administrator privileges to do this.

Once you enable CDC, it captures all of the INSERT, UPDATE, and DELETE operations on your chosen tables. The Debezium connector can then emit these events to Kafka topics.

1. Enable CDC on the database

There are two system stored procedures to enable CDC (you need administrator privileges to run these). Use sys.sp_cdc_enable_db to enable CDC for the whole database and then You can run the procedure with SQL Server Management Studio or with Transact-SQL.

Before running the procedure, ensure that:

• You are a member of the sysadmin fixed server role for the SQL Server.
• You are a db_owner of the database.
• The SQL Server Agent is running.

Then, follow the steps below to enable CDC:

1. From the View menu in SQL Server Management Studio, click Template Explorer.

2. In the Template Browser, expand SQL Server Templates.

3. Expand Change Data Capture > Configuration and then click Enable Database for CDC.

4. In the template, replace the database name in the USE statement with the name of the database where you want to enable CDC. For example, if your database was called myDB, the template would be:

   USE MyDB
   GO
   EXEC sys.sp_cdc_enable_db
   GO
   

5. Run the stored procedure sys.sp_cdc_enable_db to enable CDC for the database.

When you enable CDC for the database, it creates a schema called cdc and also a CDC user, metadata tables, and other system objects.

Keep the Change Data Capture > Configuration foldout open in the Template Explorer because you will need it to enable CDC on the individual tables next.

2. Enable CDC for the tables you want to capture

You must also enable CDC on the tables you want Debezium to capture using the following steps (again, you need administrator privileges for this):

1. With the Change Data Capture > Configuration foldout still open in the Template Explorer, select Enable Table Specifying Filegroup Option.

2. In the template, replace the table name in the USE statement with the name of the table you want to capture. For example, if your table was called MyTable then the template would look like the following:

   USE MyDB
   GO
   
   EXEC sys.sp_cdc_enable_table
   @source_schema = N'dbo',
   @source_name   = N'MyTable', 
   @role_name     = N'MyRole',  
   @filegroup_name = N'MyDB_CT',
   @supports_net_changes = 0
   GO
   

3. Run the stored procedure sys.sp_cdc_enable_table to enable CDC for the table.

4. Repeat steps 1 to 3 for every table you want to capture.

3. Check that you have access to the CDC table

You can use another stored procedure sys.sp_cdc_help_change_data_capture to query the CDC information for the database and check you have enabled it correctly. Before doing this, check that:

• You have SELECT permission on all of the captured columns of the capture instance. If you are a member of the db_owner database role then you can view information for all of the defined capture instances.
• You are a member of any gating roles that are defined for the table that the query includes.

Follow the steps below to run sys.sp_cdc_help_change_data_capture:

1. From the View menu in SQL Server Management Studio, click Object Explorer.

2. From the Object Explorer, expand Databases, and then expand your database object, for example, MyDB.

3. Expand Programmability > Stored Procedures > System Stored Procedures.

4. Run the sys.sp_cdc_help_change_data_capture stored procedure to query the table. For example, if your database was called MyDB then you would run the following:

   USE MyDB;
   GO
   EXEC sys.sp_cdc_help_change_data_capture
   GO
   

5. The query returns configuration information for each table in the database that has CDC enabled and that contains change data that you are authorized to access. If the result is empty then you should check that you have privileges to access both the capture instance and the CDC tables.

SQL Server on Azure

You can also use the Debezium SQL Server connector with SQL Server on Azure. See Microsoft's guide to configuring SQL Server on Azure for CDC with Debezium for more information.

SQL Server capture job agent configuration parameters

In SQL Server, the parameters that control the behavior of the capture job agent are defined in the SQL Server table msdb.dbo.cdc_jobs. If you experience performance problems while running the capture job agent then you can adjust the capture jobs settings to reduce CPU load. To do this, run the sys.sp_cdc_change_job stored procedure with your new parameter values.

The following parameters are the most important ones for modifying the capture agent behavior of the Debezium SQL Server connector:

• pollinginterval: This specifies the number of seconds that the capture agent waits between log scan cycles. A higher value reduces the load on the database host, but increases latency. A value of 0 specifies no wait between scans. The default value is 5.
• maxtrans: This specifies the maximum number of transactions to process during each log scan cycle. After the capture job processes the specified number of transactions, it pauses for the length of time that pollinginterval specifies before the next scan begins. A lower value reduces the load on the database host, but increases latency. The default value is 500.
• maxscans: This specifies a limit on the number of scan cycles that the capture job can attempt when capturing the full contents of the database transaction log. If the continuous parameter is set to 1, the job pauses for the length of time that the pollinginterval specifies before it resumes scanning. A lower values reduces the load on the database host, but increases latency. The default value is 10.

See the SQL Server documentation for more information about capture agent parameters.

Handling changes to the schema

RDI can't adapt automatically when you change the schema of a CDC table in SQL Server. For example, if you add a new column to a table you are capturing then RDI will generate errors instead of capturing the changes correctly. See Debezium's SQL Server schema evolution docs for more information.

If you have administrator privileges, you can follow the steps below to update RDI after a schema change and resume CDC. See the online schema updates documentation for further details.

1. Make your changes to the source table schema.

2. Create a new capture table for the updated source table by running the sys.sp_cdc_enable_table stored procedure with a new, unique value for the parameter @capture_instance. For example, if the old value was dbo_customers, you could replace it with dbo_customers_v2:

   EXEC sys.sp_cdc_enable_table @source_schema = 'dbo', @source_name = 'customers', @role_name = NULL, @supports_net_changes = 0, @capture_instance = 'dbo_customers_v2';
   GO
   

3. When Debezium starts streaming from the new capture table, drop the old capture table by running the sys.sp_cdc_disable_table stored procedure with the parameter @capture_instance set to the old capture instance name, dbo_customers:

   EXEC sys.sp_cdc_disable_table @source_schema = 'dbo', @source_name = 'dbo_customers', @capture_instance = 'dbo_customers';
   GO