Microsoft SQL Server 2012 Bible

Change Data Capture

Where change data capture shines is in gathering data for ETL from a high-traffic OLTP database to a data warehouse. Of the possible options, change data capture has the least performance hit and does a great job to provide the right set of data for the Business Intelligence ETL (extract-transform-load). When you think big-dollar BI, think CDC.

Any data written to the transaction log can be asynchronously captured using CDC from the transaction log after the transaction is complete, so it doesn't affect the original transaction's performance. CDC can track any data from the T-Log, including any DML insert, update, delete, and merge command, and DDL create, alter, and drop.

Changes are stored in change tables — tables created by CDC with the same columns as the tracked tables plus a few extra CDC-specific columns. All the changes are captured, so CDC can return all the intermediate values or just the net changes.

The new features (Considerations) for CDC introduced with SQL Server 2012 mostly fall into two main categories: AlwaysOn and External Drivers. When working with AlwaysOn Replicas there is only one way to collect the data properly. Some new third-party drivers have been developed for use with external data sources like Oracle.

For more information on the third-party drivers, see http://blogs.msdn.com/b/mattm/archive/2012/03/26/cdc-for-oracle-in-sql-server-2012.aspx.

Because CDC gathers its data by reading the log, the data in the change tables is organized ...