For an existing application I personally prefer changing the index type, partitioning the table or tuning DB parameters first. It's far less risky because you d

For an existing application I personally prefer changing the index type, partitioning the table or tuning DB parameters first. It's far less risky because you don't need to change a single query and it's transaprent to the application. Sure if you cannot get the desired perfomance by tuning the RDBMS than you need to consider changing the way how the tables are modelled. From my experience, usually normalizing it one step furhter improves the performance, at least for OLTP use cases.