We used to use FORCE INDEX hints to enable an index search for a SQL statement if a specific index is not used. It is due to the database SQL optimizer thinking that not using the specific index will perform better. But enabling an index is not as simple as just adding an index search in the query plan, it may entirely change the structure of the query plan, which means that forecasting the performance of the new Force Index hints is not easy. Here is an example to show you how to use FORCE...
How to use FORCE INDEX Hints to tune an UPDATE SQL statement?
How to use FORCE INDEX Hints to tune an UPDATE SQL statement?