Managing Concurrent Data Access
Users who access a resource at the same time are said to be accessing the resource concurrently. Concurrent data access requires mechanisms to prevent adverse effects when multiple users try to modify resources that other users are actively using.
The different levels of concurrency control have different side effects. Understanding these effects is important for picking the appropriate level of concurrency control for an application.
The concurrency control mechanisms fall into the following categories:
The transaction isolation levels define whether a transaction uses optimistic or pessimistic concurrency control and the level of protection from other transactions accessing data at the same time.