Is there a way to calculate the performance impact of adding a secondary index to a table. Either Unique or NON Unique.
If it's the first index on a table:
- a USI will double the number of IOs for Inserts/Update/Deletes and it needs communication between primary and secondary AMP, runtime might be doubled.
- for a NUSI it depends on the number of rows per value, maintaining a NUSI with a low number is much cheaper.
So it's really hard to tell without testing.