In this post, we will go into the various features of the SQL Server Change Data Capture (CDC) and its many facets. We will explore its evolution to the present form, the types of CDC, and the many benefits that it brings to organizations around the world, not necessarily in this order.
The Evolution of The SQL Server Change Data Capture
In the current business environment, organizations depend primarily on data to drive their operations. Hence, the need of the hour is to insulate their data from unscrupulous elements and hackers, assure high levels of data security, and have stringent access management procedures in place.
In the past, various processes and technical procedures have been tried by different database management systems to ensure that data is stored in a manner that does not compromise its value or history. Among the resolutions experimented with are complex queries, timestamps, triggers, data auditing, and more. However, none of these turned out to be a fail-safe solution.
It was not until 2005 that a tangible answer to this issue was found. Microsoft introduced their SQL Server Change Data Capture product with “after update,” “after insert,” and “after delete” capabilities. The technology at that time was rudimentary and DBAs found it very complex to work with.
Based on this feedback, a revised version was launched by Microsoft in 2008 and this was very well received. It enabled developers to seamlessly capture and store historical data and changes made to the database without having to go through elaborate additional programming activities.
The Working and Technology of Microsoft SQL Server Change Data Capture
Now, let us make an in-depth analysis of the functioning of the SQL Server CDC and the technology on which it is based.
How Does SQL Server CDC Work
Change Data Capture tracks all changes and modifications made by users to tables. These changes are then stored in relational tables that allow easy and quick data retrieval through T-SQL. Whenever CDC is applied to a database table, a mirror image of the tracked table is instantly created. The changes that are made to the database rows can then be identified by the architecture of the columns of the replicated tables since these have extra metadata columns.
Apart from this aspect, what is unique about this CDC feature is that the source and the replicated tables are similar in all respects. After the SQL Server Change Data Capture process is over, it is possible to track the new audit tables and use them to track the logged tables and supervise all activities that have been completed.
The source of all the changes made to the tables is reflected in the transaction logs of the SQL Server CDC. The details of any changes in the source tables, regardless of whether it is updated, deleted, or inserted, are entered in the log which then becomes an integral part of Change Data Capture. Detailed descriptions of the changes are available in the log that can be read and connected to the change table part of the source table.
The Technology of the SQL Server Change Data Capture
The technology of the SQL Server CDC is so designed that it can carry out changes such as update, insert, or delete and provide them to users in an easy-to-read relational format. The modified rows with these changes have all the inputs that are necessary to capture the changes to a target like metadata or column information. This captured information is then stored in columns that replicate those of the tracked stored tables. Access to the changed data is controlled by related and specific table-valued functions.
Now let us study in-depth why the technology of the Microsoft version of the SQL Server Change Data Capture is several notches above others in the CDC niche.
The most critical difference is that for others, changes have to be continually refreshed to be updated even though changes made at the source tables are mirrored in the target location. This is a very tedious and time-consuming process. On the other hand, change data seamlessly flows to the target databases in SQL Server CDC.
This is the reason why SQL Server Change Data Capture is preferred by organizations around the world for their IT infrastructure.
Types of SQL Server Change Data Capture
There are two types of SQL Server CDC that users have at their disposal.
Log-based CDC
In this method, CDC first reads the file and the transaction logs of the database. Users can then know the changes that have been made to the source tables and will now be replicated in the target database. The main advantage here is that this process is very reliable and there is no possibility of any change being left out and not being transferred to the target.
Trigger-based CDC
In this process, triggers are placed in the database. These are automatically set off when any changes are identified in the source database, thereby substantially reducing the expenses of extracting data.
The trigger-based SQL Server Change Data Capture has several benefits. Direct support is provided for selected databases in the SQL API, all transaction details are available in the shadow tables, and any change is implemented quickly.
On the downside though, there is an increase in the operation of the source system as the database has to be refreshed every time a change is made, thereby increasing the run-time costs. Also, triggers may get disabled during operations, thereby affecting the performance of the databases when rewrites are essential during changes made to the rows.
Overall, then, SQL Server Change Data Capture has been a big help for business to effectively manage their databases.
