When a query performs a table scan at isolation level 3 on a data-only-locked table, a shared or exclusive table lock provides phantom protection and reduces the locking overhead of maintaining a large number of row or page locks. On an allpages-locked table, an isolation level 3 scan first acquires a shared or exclusive intent table lock and then acquires and holds page-level locks until the transaction completes or until the lock promotion threshold is reached and a table lock can be granted.
