Tuesday, 21 August 2012

What is Change Data Capture and How to validate CDC in Obia?

Change Data Capture in Datawarehose  identifies the data that has been added,removed and updated.Instead of using the difficult techniques what it dose is it captures the change data resulting from INSERT, UPDATE, and DELETE operations made to user tables And this change data is then stored in a relational table called a change table.This is how CDC works.
Data warehousing  deals with a lot of extraction and transportation of data from source database to the datawarehouse. Change Data Capture identifies and processes only the data that has changed and makes the change data available for further use.

Advantages of capturing change data with Change Data Capture:

Compared to techniques like Table differencing(All data from  old_version table MINUS All data FROM new_version table ) and Change-value selection(capturing the data on the source database by selecting the new and changed data from the source tables based on the cols like Last update date) this technique is far more easy and less complicated. 
  • Captures all the data:Change Data Capture can capture all effects of INSERT, UPDATE, and DELETE operations even the changes before and after .
  • Cost: Compared to other techniques CDC is far less expensive
  • Performance :Asynchronous Change Data Capture can be configured to have minimal performance impact on the source database.

How to validate Change Data Captured?

Change Data Capture objects are exported and imported as part of full database export and import (exp and imp)operations into the Datawarehouse.After the import operation Change Data Capture objects are validated to determine if all expected underlying objects are present in the correct form. Change Data Capture generates validation warnings in the import log if it detects validation problems. Imported Change Data Capture objects with validation warnings usually cannot continue capturing change data.

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