However, if an application accesses a sequence that is not in the cache, then the sequence must be read from disk to the cache before the sequence numbers are used.If your applications use many sequences concurrently, then your sequence cache might not be large enough to hold all the sequences.
Sequences eliminate serialization and improve the concurrency of an application.
Notice that several parameters can be specified to control the function of sequences.
For example, when an instance abnormally shuts down (for example, when an instance failure occurs or a statement is issued), sequence numbers that have been cached but not used are lost.
Also, sequence numbers that have been used but not saved are lost as well.
The examples outlined in the following sections show how sequences can be used in master/detail table relationships.