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Microsoft SQL Server Change Data Capture: A Comprehensive Guide to Understand What it Does, How to Implement it and Best Practices

  • Taylor Huettner
  • Jan 28
  • 6 min read

Updated: Feb 3

Change Data Capture (CDC) has quickly become a vital tool for organizations to track their database changes whether to gain insights or for regulatory purposes. Whether you're the owner of a small business, a Database Administrator or Chief Technical Officer of a major corporation, getting the most out of change data capture will empower you to adapt quickly to your database changes or regulatory requirements. This comprehensive guide breaks down the core concepts, benefits, and practical steps for implementing CDC with Microsoft SQL Server.


What is Change Data Capture?


Change Data Capture (CDC) is a feature for databases to tracks changes (insert, update, and delete operations) on tables. Each database provider (SQL Server, Oracle, PostreSQL, MySQL) have different approaches to how they achieve this. This article is going to focus on Microsoft SQL Server specifically. Change data capture comes standard with all editions of Microsoft SQL Server except for Express as well as on SQL Server managed instances (Azure SQL, Amazon RDS SQL, Google Cloud SQL).


CDC for Microsoft SQL Server operates by creating change tables (CDC tables) that mirror your source tables and include addition metadata columns to note the operation (insert,update,delete) as well as timestamps. This functionality allows you to track changes without the need to continuously query the main database tables or adding expensive triggers. Instead, you'd access the designated CDC function directly to view the CDC data, as querying the CDC tables directly is not recommended.


CDC is particularly beneficial in data warehousing, ETL processes, and analytical reporting, as it minimizes resource consumption and helps maintain operational efficiency.


Understanding How Change Data Capture Works


The operation of Change Data Capture involves three key aspects:


  1. Change Tables: The change tables, or CDC tables, will mirror the source table with some additional columns for timestamp and the type of operation that occurred (insert, update, delete). These table are created when you enable change data capture on the respective table.


  2. Capturing Changes: As changes in your database occur, the database logs record the change to the source tables and then a CDC SQL agent job writes the event to the CDC table. This approach takes away any loads on the database since it's a log-based approach. Insert statements will create one records to show the values at the time the insert occurred. Delete statements will create one record to show the values at the time of deletion. Update statements will create one record before the update and one record after the update.


  3. Cleaning Up: It's important to establish a cleanup strategy to efficiently handle the buildup of change data. For instance, without routine cleanup, a frequently updated table could become cause the CDC tables to become excessively large, potentially causing performance problems. By default, data in the change data capture tables is automatically deleted to help prevent this.


With a good grasp of these components, the next step is implementing CDC in your SQL Server environment.


Implementing Microsoft Change Data Capture


Implementing change data capture is a little tricky due to the fact that it needs to be done by executing a couple of system stored procedure and that requires an understanding of those stored procedures and their parameters. Below is a breakdown of those stored procedures as well as the steps for executing them:


Step 1: Enabling Change Data Capture


Start by enabling CDC at the database level using the sys.sp_cdc_enable_db system stored procedure:


For traditional on-premise SQL Server instances or Azure SQL instances:

EXEC sys.sp_cdc_enable_db

For Amazon RDS SQL Server instances:

EXEC msdb.dbo.rds_cdc_enable_db

For Google Cloud SQL Server instances:

EXEC msdb.dbo.gcloudsql_cdc_enable_db

This command will turn on CDC for your specified database as well as create the necessary CDC SQL Agent jobs.


Step 2: Enabling Change Data Capture on Tables


Next, you'll need to identify which tables you will want to track. Once you have that information, you can enable change data capture on a specific table using the following command:

EXEC msdb.dbo.sp_cdc_enable_table  
	@source_schema = N'dbo',
	@source_name = N'YourTableName',
	@role_name = NULL

Parameter explanations

@source_schema - populate with the schema associated with the table you want to track

@source_name - populate with the name of the table you want to track

@role_name - populate with the role you want to associate with CDC. Only users with that role will be able to access the CDC data through the CDC functions. Leave the value NULL for general gated access.


Step 3: Monitoring Changes


Once CDC is enabled, you can monitor the changes by querying the CDC tables via the CDC table value functions. Below is an example of that command for the Adventureworks database and Department table in HR schema:


DECLARE @from_lsn AS BINARY (10), @to_lsn AS BINARY (10)
SET @from_lsn = sys.fn_cdc_get_min_lsn('HR_Department')
SET @to_lsn = sys.fn_cdc_get_max_lsn()

SELECT * FROM cdc.fn_cdc_get_all_changes_HR_Department(@from_lsn, @to_lsn, 'all')

Parameter/variable explanations:


Step 4: Managing Change Data Capture


To prevent storage issues, SQL Server change data capture will automatically remove records from the CDC tables after 3 days (4320 minutes). This is done by way of a SQL Agent job that runs at 2am each night. The SQL Agent job gets setup automatically when you enable change data capture on your database.


Step 5: Troubleshooting and Best Practices


To maintain your Change Data Capture system, follow these best practices:


  • Regular Monitoring: Review your CDC settings to verify everything operates smoothly.


  • Configure Log Retention: Develop a plan for retaining change data to manage storage effectively.


  • Performance Testing: Continuously monitor any performance impacts resulting from CDC and adjust strategies as necessary. Tables that have a large number of records (+50,000) or tables that are updated hundreds of times a day, are likely not good candidates to have change data capture enabled.


  • Data Security: Ensure any sensitive information captured through CDC is protected adequately. This is especially important for sectors dealing with confidential data.


By incorporating these practices, you will enhance your organization’s ability to manage crucial data efficiently.


Use Cases for Change Data Capture


Change Data Capture can benefit various scenarios:


  1. ETL Processes: Many companies adopt CDC to refresh data warehouses without running exhaustive extract processes, often increasing efficiency by up to 70%.


  2. Data Replication: Businesses may require real-time updates across various database environments, which CDC can facilitate.


  3. Data Auditing: Organizations complying with regulatory standards can easily maintain a historical record of data changes, simplifying audits.


  4. Reporting and Analytics: Companies can analyze captured change data to derive insights and improve decision-making. For example, retailers might use this data to adjust inventory based on recent purchasing trends.


With such diverse application scenarios, adopting CDC can be transformational for your organization’s data strategies.


Final Thoughts on Change Data Capture


Mastering Microsoft Change Data Capture is vital for any organization valuing efficient data management. By grasping CDC principles and implementing them effectively, you can achieve real-time data updates, reduce performance burdens, and streamline data workflows.


This guide has walked you through essential aspects of CDC, from basic concepts to detailed implementation steps. I encourage you to try the methods discussed and adjust them to meet your specific needs.


Where does MergeCDC come in?


  1. MergeCDC migrates the change data capture data from all of the CDC tables into a standardized central table. This makes it easy to streamline the data from multiple SQL Server databases into to a data warehouse as well as for reporting on each database instance.

  2. MergeCDC allows you to specify exactly which columns you want to track, therefore minimizing the amount of data that gets accumulated in the CDC tables as well as the central MergeCDC table. MergeCDC also removes any CDC column data that wasn't changed, eliminating even more unneeded data.

  3. MergeCDC also lets you specify the type of operations you want to migrate to the central MergeCDC table, giving you the most flexibility possible.

  4. MergeCDC ensures you do not lose any of your capture data. Data in the CDC tables is deleted after 3 days, by default. Since MergeCDC migrates the data to a central table, you can be sure you do not lose any of your change data.

  5. MergeCDC has built-in functionality to allow you to delete capture data in the central table as it becomes stagnant. Many regulatory initiatives either require businesses to keep records for 7 years and/or delete any identifiable information after 7 years. MergeCDC can do this out-of-the-box with no effort from you or your organization.

  6. MergeCDC is a pure SQL ETL solution. Meaning that it doesn't require any software to either install it or run it. As such, it's maintenance and hassle free!

  7. MergeCDC is very quick and easy to setup. Whether you're are a technical novice or a database administrator, the setup is quick and painless. If you know the tables and columns in your database that you want to track or better yet have filled out the TrackingTables.xlsx file from our Getting Started page (or link below), you are minutes away from being able to track your database changes and that can have an immediate impact on your business.

  8. MergeCDC doesn't require you or anyone in your organization to understand how change data capture works, how to implement it, how to standardize it, how to maintain it, how to query it, how to ensure there is no data loss and how to setup a strategy to prevent storage issues. This is all done for you by MergeCDC!


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