Hi Harish
Seems like you are doing the changes directly in production system. (I don't think dev system will have 3 million records).
1) If you are doing the changes in production system directly
Please don't continue. Its always good to transport the changes from dev system to QA, where you will get to know all possible issues. Correct the issues and then move it to production system.
2) If you are doing in development system
Since the job ran for 5 days, there are chances for the job got some issues in between.
And with this much amount of records, you will have more issues in next environments.
a. So create a new copy DSO and first move the data to the new DSO
b. Add the new fields in your existing DSO
c. move the data from new DSO to existing one
Hope this helps
Regards
Karthik