Posted by: Chun-Ming Chen (Bellevue College Student, WA)
Concurrency is an ability that allows multiple users to access the same data at the same time.   However as more users access the data at the same time, the greater the chance for users to change the same set of data at the same time and overwrite each other’s input. The integrity of the data is compromised without the users initiating the operations knowing it. There are four types of concurrency problems:

·       Lost updates

·       Dirty reads (uncommitted dependencies)

·       Nonrepeatable reads (inconsistent analysis)

·       Phantom reads