Locks and performance

Because a lock serializes access to one piece of data, it reduces concurrency; any other programs that want access to that data must wait. The database server can place a lock on a single row, a disk page, a whole table, or an entire database. (A disk page might hold multiple rows and a row might require multiple disk pages.) The more locks it places and the larger the objects it locks, the more concurrency is reduced. The fewer the locks and the smaller the locked objects, the greater concurrency and performance can be.