It is observed that the exactly-once processing is not working correctly.
The reason for this is that when the operator crashes, it comes back and
inserts data again for non-checkpointed windows.
Hence redundant rows are added in the table. The fix is simple and
suggested by Sandeep is to add a check in endWindow() not to update the
meta data in output store.
I will do the required code change add a corresponding unit test case and
open PR (if there are no objections).