Analyzing SQL Server Change Data Capture (CDC)

Before diving into the intricacies of SQL Server CDC, let us understand broadly what the Change Data Capture technology is all about.

Change Data Capture

Change Data Capture is a software pattern that has assumed great importance in the modern data-driven business environment. It assures data durability and safety and ensures that data is insulated from breaches. Most importantly, Change Data Capture makes sure that any changes made to a database are accurately recorded without affecting its history.

There have been many attempts to achieve this goal in the past. Solutions like triggers, data audits, timestamps, and complex queries were tried, but none of them offered the desired results until Microsoft came up with its SQL Server CDC feature.

Development of SQL Server Change Data Capture

Microsoft launched its SQL Server CDC product in 2005. Though it had “after update,” “after insert,” and “after delete” capabilities, the technology was at its rudimentary stage, and users found it very complex to work with. This led Microsoft to introduce a revised version in 2008, which was very well received by the users and became so popular that it is still used today.

In this form of SQL Server CDC, users could quickly and seamlessly capture and store changes made to a database and historical data without going through elaborate and additional programming tasks.

Technology of SQL Server Change Data Capture

Let us make an in-depth analysis of this pathbreaking format of SQL Server CDC.

Here, Change Data Capture tracks and monitors all changes made to user tables in a database. Once identified, these changes are stored in relational tables to be easily and quickly retrieved through T-SQL whenever required.

It is important to note here that in the event of CDC being applied to a database table, a mirror image of the tracked table is immediately created. These changes made to the database rows can then be recognized by the structure of the columns of the replicated tables, as they have additional metadata columns.

Except for the extra metadata columns, the unique aspect of SQL Server CDC is that the architecture of the source and the replicated tables is the same in all other respects. After completing the Change Data Capture process, it is possible to track the new audit tables and use them to monitor the logged tables and all other activities done by CDC.

The transaction logs of SQL Server CDC reflect the source of all the changes made to tables. The details of all the changes in the source tables are entered in the log to become an integral component of Change Data Capture. This is regardless of the classification of the changes, which are insert, delete, or update of data. Detailed descriptions of the changes can be seen in the log and can be read and linked to the changed part of the source table.

Why is SQL Server CDC a leader in this niche?

Now, let us understand why the Microsoft Change Data Capture version is a leader in the field of CDC.

The technology of SQL Server CDC is designed to carry out all types of changes, such as Update, Insert, and Delete. These changes at the source tables are available to users in an easy-to-read and understand relational format. Further, the modified rows with these changes have all the metadata and column information required to capture these changes to a target table.

This captured information is then stored in columns that mirror the columns of the tracked stored tables. Keeping data security and the history of the data before the changes in mind, access to the changed data is strictly controlled through related and table-valued functions.

Now, we will come to why SQL Server CDC is an optimized technology. In other Change Data Capture products, changes made to the databases have to be continually refreshed, making it a complex and time-consuming process. On the other hand, in SQL Server Change Data Capture, change data moves seamlessly to the target databases.

These are the attributes that make the SQL Server Change Data Capture technology a cut above its competitors.

Types of SQL Server Change Data Capture

There are two types of SQL Server CDC, and businesses can choose one that meets their CDC requirements.

Log-based CDC

In this form of SQL Server Change Data Capture, the system first examines the file and the transaction log of the database. This step helps users get information about all the changes made at the source. In the next step, all the changes that are made at the source database are replicated in the target database.

Benefits of Log-based CDC.

The process is very reliable because there is no chance of accounting for the changes made.
This type of SQL Server CDC has no effect on the production database system. This is because its schemas are neither required to be changed nor is there a need to add new tables.

Downside of Log-based CDC

This method works only with databases that are compatible with log-based CDC.

Trigger-based CDC

In this form of CDC, triggers are placed in the databases that are automatically set off when a change is identified in the source database.

Benefits of Trigger-based CDC

Reduced costs of extracting changes made to source tables.
Direct support for selected databases in the SQL API.
Finding details of all transactions in the shadow tables
Faster implementation of changes.

Downsides of Trigger-based CDC

Rise in system operating cost due to an increased run time of the source system, as the database must be refreshed every time a change is made.
Triggers may be disabled during operations, and the performance of the databases may be adversely affected. This happens when rewrites become necessary during changes being made to the rows.

SQL Server CDC is today an indispensable tool for data-driven businesses.