Once CDC is enabled, it creates the corresponding objects are created: cdc schema, cdc user, metadata tables and other system objects. The thing about this is that you have to enable it on a per table basis (I don't know why Microsoft chose to do it this way but if you decide to do this on all user-defined tables, you definitely need to write a script to accomplish this)
EXEC sp_cdc_enable_table 'dbo', 'EmployeeTerritories', @role_name = 'cdc_role';
Just to explain the parameters passed to the stored procedure, the dbo happens to be the schema in which the table belongs, EmployeeTerritories is the name of the table which will be enabled for CDC while the @role_name parameter is the name of the database role used to have access to change data. If the role already exists, permissions are given to that role. If it doesn't, it will be created with the specified name. Now, let's simulate changes in the dbo.EmployeeTerritories table (don't worry about referential integrity as this has been taken cared of)
INSERT dbo.EmployeeTerritories VALUES (4,98004), (4,98052);
WAITFOR DELAY '00:00:05';
UPDATE dbo.EmployeeTerritories SET TerritoryID =80202
WHERE employeeid = 4 AND TerritoryID=98052;
These information is stored in a new table created named schema_table
DECLARE @begin_time datetime, @end_time datetime, @from_lsn binary(10), @to_lsn binary(10);
-- Obtain the beginning of the time interval.
SET @begin_time = GETDATE()-1;
-- Obtain the end of the time interval.
SET @end_time = GETDATE();
-- Map the time interval to a change data capture query range.
SELECT @from_lsn = sys.fn_cdc_map_time_to_lsn('smallest greater than or equal', @begin_time);
SELECT @to_lsn = sys.fn_cdc_map_time_to_lsn('largest less than or equal', @end_time);
-- Return the changes occurring within the query window.
SELECT * FROM cdc.fn_cdc_get_all_changes_dbo_EmployeeTerritories(@from_lsn, @to_lsn, 'all');
You might notice the new function introduced - fn_cdc_map_time_to_lsn. This just returns the log sequence number (which we don't really care about) corresponding to the specified time (which we are more familiar with). The resultset would be something we could understand. What we need to really look at is the __$operation column which returns code values for the operations done for the specified table: 1 = delete, 2 = insert, 3 = update (before image), and 4 = update (after image). Imagine an UPDATE statement to be like a DELETE followed by an INSERT that's why you have a before and after images. Another way to translate the results of the cdc.dbo_EmployeeTerritories_CT table is to use the query below
operation = CASE __$operation
WHEN 1 THEN 'DELETE'
WHEN 2 THEN 'INSERT'
WHEN 3 THEN 'UPDATE(BEFORE)'
WHEN 4 THEN 'UPDATE(AFTER)'
ELSE 'UNDEFINED' END,
Bear in mind though that the data in the cdc tables are available within 3 days expressed in minutes (4320). You can clean this up when necessary using the sp_cdc_cleanup_change_table stored procedure.
This gives you an overview about change data capture and how you can use it in SQL Server 2008. Download the RC0 and start playing around with it. Check out my SQL Server 2008 videos at BlogCastRepository.com