Client requested to audit all user SQL statements to check who is accessing the data. We are going to implement `execute' audit policy. How much it will impact performance of the database??
The overhead depends on the type of implemented audit policies, whether it is WITH DATA or WITHOUT DATA, and the available resources, and the type of workload run on the system.
To give an example, if you run an analytic workload with long-running queries and you want to log every statement, there is less relative overhead than in an OLTP system with gazillion short-running queries.
Overall I would expect single digit overhead. You want to run queries, not audits... :)