What Makes Oracle Different?

There are, of course, many ways in which Oracle differs from other RDBMSs, but from a developer’s perspective, possibly the two major concepts to understand are Oracle’s locking mechanism and its multiversion read consistency model.

Oracle’s Locking Mechanism

Locks (and latches) are constructs used to regulate concurrent access to a shared resource within Oracle. These constructs play a crucial role in maintaining data integrity during concurrent modification of the shared resources. In Oracle, a shared resource is not just your data; it could also be your code (e.g., a PL/SQL package procedure cannot be altered when it is being executed).

Oracle automatically obtains necessary locks to execute SQL statements; in general, users need not be concerned with managing locks in Oracle. The following are some important facts about Oracle’s locking policy: