Which type of lock prevents Write and Exclusive locks?

The type of lock that prevents Write and Exclusive locks is a Read Lock. When a Read Lock is applied to a database object, it allows multiple users to read the data simultaneously, but it effectively blocks any Write or Exclusive locks from being acquired on that object. This restriction ensures that the data remains consistent and unaltered while the reading operation is occurring.

In typical scenarios, a Read Lock is used when you need to ensure that the data being accessed will not change during the read process, thus preserving the integrity of the data retrieved. Since Write and Exclusive locks are more stringent and involve modifications to the data, the Read Lock prioritizes the reading process, allowing it to coexist with other Read Locks but not with any operations that would alter the data.

Other types of locks, such as Exclusive and Write locks, inherently restrict access for other transactions, creating a more significant barrier to concurrency in the database system. Therefore, the Read Lock's ability to permit concurrent read access while blocking writes is what makes it the correct choice in this context.