SQL Server on Google Cloud SQL

When CDC is enabled for a table and changes occur to it, change events are persisted to a 'change table' on the SQL Server database server.

If you introduce a change in the structure of the source table, for example, by adding a new column, that change is not reflected in the change table.

For as long as the change table continues to use the outdated table structure, the Streamkap SQL Server Source is unable to capture change events for the table correctly.

You must intervene to refresh the change table structure because of the way that CDC is implemented in SQL Server.

Refresh change table structure (Online)

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Online refresh limitation

In the interval between the source table structure changing in the source database, and _before _the change table structure is refreshed, change events continue to be captured with the outdated table structure.

For example, if you added a new column to a source table, change events that are captured before the change table is refreshed will not contain the new column.

If this cannot be tolerated, an Offline refresh has to be performed. However, that means downtime for whatever system made structural changes to your tables and your Streamkap pipelines.

Please contact us for assistance if an Offline refresh is required.

The procedure for completing an Online refresh is simpler than running it Offline, and you can complete it without any downtime to your systems and Streamkap pipelines.

For every source table that has changed, copy paste the script below into SQL Server Management Studio, change placeholders as required, and then run all queries.

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If you're not sure what {refresh_table} name to use, use {schema}_{table}_v{N}. For example, if the source table is sales.orders then you'd use sales_orders_v2

-- Replace {database}, {schema} and {table} placeholders
-- {database}: name of the CDC enabled database
-- {schema}: name of the schema with tables to refresh
-- {table}: name of the table to refresh
-- {refresh_table}: a unique name for the refreshed change table
USE {database};
GO
EXEC sys.sp_cdc_enable_table
@source_schema        = N'{schema}',
@source_name          = N'{table}',
@role_name            = N'streamkap_role',
@filegroup_name       = N'Streamkap_ChangeTracking',
@supports_net_changes = 0,
@capture_instance     = N'{refresh_table}'
GO

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Refresh table limitation

There cannot be more than 2 change tables for every source table.

After refreshing a change table using the above script, confirm with Streamkap Support that your SQL Server Source has started streaming from the refreshed change table. Once confirmed, disable CDC on the outdated change table. Use the script below to do that.

SQL

-- Replace {database}, {schema}, {table} and {refresh_table} placeholders
-- {database}: name of the CDC enabled database
-- {schema}: name of the schema with the table refreshed earlier
-- {table}: name of the table refreshed earlier
-- {refresh_table}: name of the previous refresh table, usually {schema}_{table}
USE {database};
GO
EXEC sys.sp_cdc_disable_table
@source_schema        = N'{schema}',
@source_name          = N'{table}',
@capture_instance     = N'{refresh_table}'
GO

If you're getting this error message when refreshing the change table structure, it's because there cannot be more than 2 change tables for every source table.

To fix the problem, 1 of the 2 change tables for the source table need to be disabled. The scripts below can help you do that.

-- Replace {database}, {schema} and {table} placeholders
-- {database}: name of the CDC enabled database
-- {schema}: name of the schema with the table refreshed earlier
-- {table}: name of the table refreshed earlier
USE {database};
GO

EXEC sys.sp_cdc_help_change_data_capture
@source_schema = N'{schema}',
@source_name   = N'{table}'
GO

The above script should return 2 results, the 2 change tables for the {table} specified. Typically you would disable the oldest change table, so use the create_date column to identify the oldest one.

When you've identified the change table to disable, use itssource_schema, source_table and capture_instance names in the query below and execute. Then, try your refresh table script again.

-- Replace {database}, {schema}, {table} and {refresh_table} placeholders
-- {database}: name of the CDC enabled database
USE {database};
GO
EXEC sys.sp_cdc_disable_table
@source_schema        = N'{source_schema}',
@source_name          = N'{source_table}',
@capture_instance     = N'{capture_instance}'
GO

There can be a number of reasons. The most common are misconfiguration of CDC and privilege grants.

To diagnose, run the following script:

-- Replace {database} placeholder
-- {database}: name of the CDC enabled database
USE {database};
GO

EXEC sys.sp_cdc_help_change_data_capture
GO

If the query returns an error or no results check:

• you are connected to the SQL Server database with a user that has DB_OWNER role privileges.
• if the EXEC sys.sp_cdc_help_change_data_capture stored procedure returns no results, the source tables you want Streamkap to capture may not be CDC enabled.

If the query returns results, check:

• the table(s) captured by the Connector are listed.
• there are capture_instances for the capture tables.
• the database user or role used by the Connector are members of the rolename for the capture table(s).

If you are still having issues after following the above steps, please don't hesitate to reach out to us.

There can be many reasons for the Setup scripts to fail, but the scripts below can help you diagnose the issues.

-- Replace {database} placeholder
-- {database}: name of the CDC enabled database
USE {database};
GO

SELECT name, database_id, source_database_id, compatibility_level, is_read_only, state, state_desc, is_in_standby, is_cleanly_shutdown, is_cdc_enabled, is_encrypted, replica_id
FROM sys.databases
WHERE name = '{database}' AND is_cdc_enabled=1;

EXEC sys.sp_cdc_help_change_data_capture
GO

If any of the queries return an error or no results:

• Check you connected to the SQL Server database with a user that has DB_OWNER role privileges
• If the SELECT ... FROM sys.databases ... returns no results, the database you want Streamkap to capture may not be CDC enabled
• If the EXEC sys.sp_cdc_help_change_data_capture stored procedure returns no results, the source tables you want Streamkap to capture may not be CDC enabled

If you are still having issues after following the above steps, please don't hesitate to reach out to us.