What is the Change Data Capture (CDC) feature in Microsoft SQL Server? How did it evolve to its present form? What are its features and types? This post will give readers a detailed overview of Microsoft SQL Server CDC and all the benefits it brings to organizations around the world.
So, let’s dive straight in.
What is Change Data Capture (CDC)
In the modern business ecosystem, almost all the various functionalities of an organization are data-driven. The focus today is on maintaining a high level of data safety and security as part of the IT infrastructure and firewalling data from hackers and unscrupulous elements.
It is here that Change Data Capture comes into the picture by ensuring that data is stored in systems in a way that its value and history are not compromised. The concepts behind the process are not new. Various solutions have been experimented with in the past to heighten data security like using data auditing, timestamps, complex queries, triggers, and more. However, before the CDC came along, none of these proved to be a fail-safe solution to data security.
The Evolution and Growth of SQL Server CDC
The software giant Microsoft was the pioneer of the Change Data Capture feature. It launched SQL Server CDC in 2005 with all the necessary and critical features such as “after update”, “after insert”, and “after delete” ones. However, the functioning of these features in that form was not easy and DBAs found them quite complex to work on.
Based on this feedback, Microsoft a modified and vastly improved version of the SQL Server CDC in 2008. This solution was well-received as it could capture and archive historical data seamlessly without first going through a host of superfluous activities simply to set up the systems. This user-friendly version of the SQL Server CDC became very popular and is still the most widely used CDC platform today.
The Functioning of Microsoft SQL Server CDC
The USP of the functioning of SQL Server CDC is its simplicity and ease of operations. It records all changes made to data such as insert, update, or delete, and presents it to the user in a straightforward relational format. The necessary changes that are required to be captured to be updated in the target database like metadata and column information can also be seen in the modified and changed rows.
These changes are then noted in tables that have a similar structure to the tracked stored tables. Further, data security is given a lot of importance here, being rigidly controlled through table-valued functions. To understand better how the SQL Server CDC, check the ETL (Extract, Load, and Transform) application activity. It moves changed and modified data to a data warehouse from the source tables that are present in the SQL Server.
The question now is why is SQL Server CDC considered to be a cut above other similar solutions offered by others. It is primarily because SQL Sever CDC has some cutting-edge capabilities that others do not have. Some providers today offer a version where users must continually refresh the source tables in the database system that copies the changes made to the data. This is a very complex and long-drawn-out affair. In comparison, the advanced SQL Server CDC ensures that changes to the data in the source database flow seamlessly to the target database.
The Workflow of the Microsoft SQL Server CDC
The Change Data Capture tool of Microsoft SQL Server monitors all changes that are made to the tables. These tracked tables are then stored in relational tables that can be accessed quickly with T-SQL. Whenever a change through CDC is applied to a database table a corresponding image is replicated to a tracked table.
The type of changes made in the source database row is recognized by the metadata columns that are present in the structure of the copied table. Apart from this minor difference all other data in the source and the target databases are the same. Once an SQL Server CDC activity is completed the new audit tables can be used for tracking the logged tables.
The reason for any change made in the source database can be seen in the transaction log. This is possible because immediately after any change is seen in the source tables, it is automatically updated and replicated in the change table part of the original table.
Types of Microsoft SQL Server CDC
Though there are two forms of SQL Server CDC, businesses generally check whether the first one fulfills their requirements before moving on to the other.
# Log-based CDC
In this type of CDC, all changes made at the source database are monitored by the system through the file and transaction log of a database. These are then replicated in the target database. The benefit of this process is that it is very reliable and no changes are overlooked. It also does not lower the performance of the databases since the schemas are not changed or added to the tables.
The drawback of this process is that it can be used only with databases that are compatible with log-based CDC.
# Trigger-based CDC
This process is relatively simple as it is partially automated. Triggers that are placed in the database are set off whenever any change is identified. However, the CDC activity takes more time here as the database has to be continually refreshed. The main benefit of this type of CDC is that due to the triggers, implementation is easier. Moreover, detailed logs are available of all transactions and direct support is provided to SQL API for certain types of databases.
The downside here is that triggers often get disabled when a large number of operations take place. This adversely affects the performance of the databases.
