When you are working with an online (shared) database, it is common for more than one user to access the database, or more specifically, the same record (row) simultaneously.  What does the software do in this situation?

This type of DB access is known as currency control.  It is a critical concept in DB administration.  There are typically three types of concurrency control:

[1] Pessimistic concurrency control - a row is unavailable to users from the time the record is first accessed until it is updated in the database.

[2] Optimistic concurrency control - a row is unavailable to other users only while the data is actually being updated. The update examines the row in the database and determines whether any changes have been made. Attempting to update a record that has already been changed, results in a concurrency violation.

[3] "Last in wins" - a row is unavailable to other users only while the data is actually being updated. However, no effort is made to compare updates against the original record; the record is simply written out, potentially overwriting any changes made by other users since you last refreshed the records.

 

Conduct some research and discuss what you find.