Row locks are used to prevent lost updates and other types of transaction inconsistencies by ensuring that any row modified by a transaction cannot be modified by another transaction until the first transaction completes, either by committing the changes by issuing an implicit or explicit COMMIT statement, or by aborting the changes via a ROLLBACK statement.

There are three classes of row locks: read (shared) locks, write (exclusive) locks, and intent locks. The database server acquires these locks automatically for each transaction.