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Visit Stack Exchange Database Administrators Stack Exchange is a question and answer site for database professionals who wish to improve their database skills and learn from others in the community. Sign up to join this community I was not aware of this question when I answered the related question ( Are explicit transactions needed in this while loop?
when you perform update of non-indexed column by some condition.
Updating very large tables can be a time taking task and sometimes it might take hours to finish.
In addition to the clustered index update, the index ix_col1 is also updated.
The index update and Sort operation together take 64% of the execution cost. Removing index on the column to be updated The same query takes 14-18 seconds when there isn’t any index on col1.
Needless to say, this is ideally an offline operation.
In addition to this, it might also cause blocking issues.