In this post, we will explore the various aspects of the Microsoft SQL Server Change Data Capture feature. Points covered are what the technology is behind the Change Data Capture software, the evolution of SQL Server Change Data Capture, its functioning, and type.
Let us start by exploring Change Data Capture (CDC) as a standalone entity.
Change Data Capture
In the modern business environment where operations are largely data-driven, most companies regardless of the scale or the type of industry seek to have measures to firewall their databases. Their focus is to have fool-proof data security and safety in place as well as measures that assure data security and integrity.
This is more than ensured by the Change Data Capture feature. It guarantees that any changes made to databases are stored and used in a manner that does not have any effect on their structure, values, and history without compromising on the required strict data security norms.
Attempts to have an optimized CDC feature have been made several times in the past with solutions that meet the needs of businesses. These have ranged from data auditing, intricate queries, timestamps, and triggers placed in source databases that were set off whenever any changes were made in the source database.
However, none could meet the expectations and offer the desired results until Microsoft launched its SQL Server Change Data Capture software design pattern.
The Launch and Evolution of MS SQL Server CDC
It was in 2005 that the Microsoft SQL Server CDC first saw the light of day. What made it special was that it included all three forms of database changes possible – “after update” “after insert” and “after delete” capabilities. However, being in the nascent stage, it needed more refining as DBAs found it rather unwieldy and cumbersome to work with.
Not the company to rest on its oars, Microsoft took cognizance of the feedback and started restructuring this feature. In 2008, it introduced a new version of the SQL Server Change Data Capture that was very user-friendly and helped DBAs to capture and store changes to the source database without going through elaborate configuration or setting up processes. This version met the required standards, was very well-received, and is still in use today.
The Attributes and Functioning of Microsoft SQL Server CDC
Attributes of SQL Server CDC
The goal of the SQL Server CDC software is not complex, it was designed to present to users changes to databases like Update, Delete, and Insert in an easy-to-understand relational format. Further, the changed and the modified rows had all the inputs required to capture changes made in the source database such as column information and metadata.
The changes that are made in the source database are mirrored in the column information in the target database or any other location. All changes made in the source database are protected through table-valued firewalls and access to them is strictly regulated as they are not an open-end data storage facility.
How does the SQL Server CDC stand up against the competition in this niche? Its advanced features, attributes, and capabilities differentiate it from the crowd. In other forms of CDC, users need to refresh the source tables at pre-determined intervals to capture changes made before replicating them to the target databases. Handling this activity thereby becomes a very time-consuming and complex affair.
In comparison, without repeated refreshing of source databases, SQL Server CDC provides an unbroken chain of changed data to be put in any application or table whenever the need arises. Take the example of the ETL (Extract, Transform, Load) application, the technology that drives SQL Server CDC. The change data in the source tables of SQL is migrated to a data storage repository or a data warehouse by the ETL application.
Functioning of SQL Server CDC
The purpose of the CDC is to monitor all changes made to the tables that are stored in the source database to be accessed and retrieved later with T-SQL. Once the CDC technology is applied to a database table, a corresponding replicated image is created of the tracked table. Further, the format of the changes made to rows in the source database is verified by additional columns of metadata present in the structure of the tables that are replicated.
This is the only point of difference between the source and the replicated tables with all other characteristics of the two being similar in all respects. When DBAs initiate any function in SQL Server Change Data Capture for tracking logged tables they get access to the current audit tables.
The transaction log of SQL Server CDC reflects all changes made in CDC. Whenever a change occurs in the tracked source tables, it is recorded in the log which is linked to the table part of the source table along with the details of the changes made.
Types of SQL Server Change Data Capture
Log-based and trigger-based are the two forms of SQL Server CDC currently in use. While businesses can choose one or the other, it makes sense to activate the second after the first one has been done.
Log-based SQL Server CDC
It is a simple and straightforward process where changes made are present in the log and file. These changes are then replicated to the target location. It is a very dependable form of SQL Server Change Data Capture because all changes are included in the replicated tables and there is no necessity to change the schemas of the production.
Trigger-based SQL Server CDC
Here, triggers placed in the source tables are set off automatically whenever a change occurs in the source database. This process is best done after log-based CDC has been implemented and only incremental changes are recorded with the trigger-based function.
