See the contents pages of the books for a detailed listing. NET 2.0 introduced a number of new Web controls designed for accessing and modifying data.Therefore, whatever manager clicks the Update button last will have his or her changes saved, overwriting the other's.The following figure illustrates this workflow when Manager A - the manager who updates the unit price to .00 - clicks the Update button after Manager B has already saved his changes.These controls allow page developers to declaratively access and modify data without writing any code to perform the data access. ) Because multiple users can visit the same web page concurrently, it is possible for a user visiting a data modification page to inadvertently overwrite the modifications made by another user. If two users visit this page simultaneously from different computers and both edit the same row, whomever saves the first will have her changes overwritten by whomever saves the row last.This article is one in a series of articles on ASP. This type of behavior is known as "last write wins" and is the default behavior for web applications.She clicks the Edit button and starts to make her change.At the same time, the other manager visits the page and sees the unit price below .00 and, noting store policy, decides to mark it as discontinued.
Optimistic assumes that concurrency violations are rare and that if such an error occurs that it's adequate to ask one of the conflicting parties to re-enter their information.In many web applications users can only modify data specific to their account, so there's no concern or need for concurrency control.But in applications where concurrency conflicts may occur, it's worthwhile to consider adding some form of concurrency control.The only way to guarantee that concurrency conflicts cannot occur is to limit data modification to one user at a time.Such draconian forms of concurrency control are referred to as pessimistic concurrency control.