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The Change Data Capture (CDC) Feature in Microsoft SQL Server

 Several issues are faced by organizations today in the areas of data security and safety and ramping up systems for preservation of historical data. Leading database platforms took steps in this regard by launching data audits, timestamps, complex queries, and triggers, one of them being Microsoft. It led the innovation when in 2005, it introduced the SQL Server CDC with the “after date”, “after delete”, and “after insert” features.


SQL Server CDC captures and records all activities like insert, update, or delete that are applied to a SQL Server table. Changes made are available in a user-friendly relational format and metadata and information that are required for posting changes to the target databases are captured in modified rows. These are stored in change tables with the same structure as the columns in the tracked source tables. SQL Server CDC also tracks and records changes in the mirrored tables with column structures that are the same as the source tables. This is excluding the Insert, Update, and Delete activities.

The following data is present in the additional columns that also track changes made at the source tables. 

·        __$start_lsn and __$end_lsn that show the commit log sequence number (LSN) assigned by the SQL Server Engine to the recorded change

·        __$seqval that shows the order of that change related to other changes in the same transaction, __$operation that shows the operation type of the change, where 1 = delete, 2 = insert, 3 = update (before change), and 4 = update (after change)

·        __$update_mask that is a bitmask defined for each captured column, identifying updating columns

These are some attributes of SQL Server CDC.

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