There are 1,500 indexes and 2,300 stats beginning with dta on one of our databases.
I read that SQL Database Tuner sometimes leaves dta indexes behind, which are hypothetical indexes and stats. But, when I check the properties of these, is_hypothetical is equal to 0.
Why is this?
I'd ideally like to delete all of these to try improve performance, but the fact they are not hypothetical I am unsure whether I should do so.
It just means that someone blindly accepted the recommendations of the database tuning advisor and told it to build all the recommended indexes and stats.
Chances are you will discover lots of them can be combined or just outright deleted.
You'll find some useful links here for investigating likely candidates for removal. How to determine if an Index is required or necessary