CHANGE_TRACKING_MIN_VALID_VERSION keeps changing even there are no changes in that table

Question

Hi,
We use stored procedure like below to get the data on intial load as well as subsequent changes. The underllined part of the stored procedure to get the last_sync_version is slightly different from what Microsoft has suggested. (not using CHANGE_TRACKING_CURRENT_VERSION).
That is because we download data to staging from multiple sources and from their we want to process data from one source at a time (DATA_SOURCE_KEY filter). 
What we notice is that, when there is no data for a table for sometime, once the change tracking gets purged for that table, we keep hitting the condition @LastVersionId <@MinVersionId. The MIN_VALID_VERSION keeps changing even though there is no change
in that table. Looks like the MIN_VALID_VERSION is a global number and not specific to a table. Is there a problem with the way we are getting the @Next_Version. Can we use the CHANGE_TRACKING_CURRENT_VERSION even though we want to download subset of data
from the table (only records matching for one data_source_key at a time). Appreciate your answers.
CREATE PROCEDURE  [dbo].[PDW_GetSiteDVAudit](@DataSourceKey AS INT,@LastVersionID AS BIGINT, @NextVersionID AS BIGINT OUTPUT)
AS
BEGIN TRY
BEGIN TRANSACTION
BEGIN
DECLARE @MinVersionID bigint = 0, @max_version bigint = 0;
SELECT @NextVersionID = 0;
SET @MinVersionID = CHANGE_TRACKING_MIN_VALID_VERSION(OBJECT_ID('dbo.SiteDVAudit'));
IF (@LastVersionID < @MinVersionID)
BEGIN
SELECT @NextVersionID = isnull(MAX(SYS_CHANGE_VERSION),@MinVersionID) from CHANGETABLE(CHANGES SiteDVAudit , NULL) CT where DataSource_Key = @DataSourceKey
SELECT 
s.Id,
Site_Id ,
SiteDesc,
Deleted,
Local_Id,
s.DataSource_Key,
Data_Task_Id
FROM 
dbo.SiteDVAudit  s
WHERE
                        s.DataSource_Key = @DataSourceKey
END 
ELSE
BEGIN
SELECT @NextVersionID = isnull(MAX(SYS_CHANGE_VERSION),@LastVersionID) from CHANGETABLE(CHANGES SiteDVAudit , @LastVersionID) CT where DataSource_Key = @DataSourceKey
SELECT 
s.Id,
Site_Id ,
SiteDesc,
Deleted,
Local_Id,
s.DataSource_Key,
Data_Task_Id
FROM 
dbo.SiteDVAudit  s
RIGHT OUTER JOIN 
CHANGETABLE(CHANGES SiteDVAudit, @LastVersionID) CT
ON s.Id = CT.Id  AND
s.DataSource_Key = CT.DataSource_Key
WHERE
                        s.DataSource_Key = @DataSourceKey
END
END
COMMIT TRANSACTION
END TRY
BEGIN CATCH
ROLLBACK TRANSACTION
RETURN -1
END CATCH

Answer 1

My first observation is that you don't reraise the error in the CATCH handler. That is bad, because it makes the proceedure fail silently which may be very difficult to troubleshoot.
The version numbers for Change Tracking are indeed database-global. MIN_VALID_VERSION can be different for different tables, if they have different retention periods. But if they all have the same retention period, it seems likely that MIN_VALID_VERSION
would increase as the database moves on.
I'm not sure about your question Can we use the CHANGE_TRACKING_CURRENT_VERSION even though we want to download subset of data from the table (only records matching for one data_source_key at a time). Where would you use it? How would you use
it?
Erland Sommarskog, SQL Server MVP, [email protected]