Q & A about the CDC Function

When explaining the new features of SQL Server Bi yesterday, I mentioned an enhancement of SQL Server 2008 database engine, namely, Change Data Capture (CDC): Change Data Capture.

It seems that everyone is interested in this function, and many people ask questions. Let me sort out the key points.

1. What is the purpose of CDC?

CDC is a mechanism that greatly facilitates us to obtain updates to a table. It uses an independent process to asynchronously read log files, rather than triggers. In addition, its data is stored persistently in a system table.

2. Is CDC a feature unique to SQL Server 2008? Does it work for other databases or earlier versions?

CDC is a feature unique to SQL Server 2008 and exclusive to the Enterprise Edition. The development edition also provides this function, but it is only used for testing purposes.

 

3. What if the log is truncated when the CDC reads the log?

If a part of the log is not read by the CDC process, the part is ignored when the log is truncated.

The capture process is independent and starts as the proxy service starts. The interval between the two scans is 5 minutes.

 

4. Will the data in the system table exist permanently?

No, it will be retained for 3 days. There will be a job to clean up, scanning at 2 o'clock every night.

 

Finally, the CDC function depends on the agent service, because both operations are started through jobs.