I am using the SQL Server 2008 R2 Database tuning advisor to tune one database which is used by a 3 rd party ERP system. At the moment this ERP application does have some serious performance issues in specific actions performed by users.
I used SQL Server profiles to trace their production database for few hours during busy time of the day. Last night I let the database tuning advisor chew the trace and it came up with a lot of recommendations and a promised performance gain of 89% !!
So now, I have understand that from the recommendations I should first create recommended clustered and unique indexes and then redo the trace and tuning.
Is it possible that by creating a clustered index I some how break the application functionality ?
No, creating CLUSTERED INDEX / UNIQUE INDEX certainly won’t break your application from a functional perspective since these would be helpful during retrievals where the index would be consulted instead of performing a table scan. They don’t impose any constraint on how the data should be stored in the tables like integrity constraints (PRIMARY KEY, UNIQUE KEY, FOREIGN KEY etc.,).