Microsoft SQL Server 2016 Standard edition supports database level audits starting from Service Pack 1. Therefore, migrating DB1 to a named instance on a server that runs Microsoft SQL Server 2016 Standard edition will allow you to perform auditing at the database level for DB1.
You can address index fragmentation by reorganizing indexes, which helps to improve query performance. Reorganizing an index is a less intensive operation than rebuilding and can be done online. This solution is appropriate for optimizing query performance in a fragmented database.
Rebuilding all indexes is an effective solution to optimize query performance in the case of index fragmentation. Rebuilding indexes recreates the indexes and eliminates fragmentation. Therefore, it is a correct approach to meet the stated goal of optimizing query performance.
Running the DBCC CHECKDB command checks the logical and physical integrity of the database but does not address fragmentation or optimize query performance. To optimize query performance when there is fragmentation, you would need to reorganize or rebuild the indexes. Therefore, the solution does not meet the goal.
To grant an auditor permission to view SQL Server audit logs while adhering to the principle of least privilege, the 'View Server State' permission should be granted. This permission allows the auditor to view server state information, which includes audit logs, without providing unnecessary elevated privileges that roles like 'sysadmin' would. This ensures the principle of least privilege is maintained.