Concurrent Access to a Sequence

A sequence always generates unique values within a database without perceptible waiting or locking, even when multiple users refer to the same sequence concurrently. When multiple users use NEXTVAL to increment the sequence, each user generates a unique value that other users cannot see.

When multiple users concurrently increment the same sequence, gaps occur between the values that each user sees. For example, one user might generate a series of values, such as 1, 4, 6, and 8, from a sequence, while another user concurrently generates the values 2, 3, 5, and 7 from the same sequence object.