* Watermark allows the poll scope to poll for new resources instead of getting the same resource over and over again.

* The database table must be ordered so that the “watermark functionality” can move effectively in the ordered list. Watermark stores the current/last picked up “record id.”

* If the Mule application is shut down, it will store the last picked up “record id” in the Java Object Store and the data will continue to exist in the file. This watermark functionality is valuable and enables developers to have increased transparency.

* Developers do not need to create code to handle caching; it is all configurable!

* There are two columns and both are unique but user_id can't guaranty sequence whereas date_time will always be in increasing order and table content can easily be ordered on the basis of last processed date_time.

So correct answer is: Set the watermark column to the date_time column