Chapter 11. Understanding Concurrency and Locking

You need to establish some rules and locking mechanisms to guarantee data integrity in case more than one user tries to update the same row of data in a multi-user database environment. DB2 uses four isolation levels to support different levels of concurrency. Each isolation level is implemented by slightly different locking behavior. In this chapter we will look at their differences and some examples on how they can be used in the application. As a database administrator or an application developer it is very helpful to know troubleshooting skills to identify locking problems, and this chapter covers DB2 monitoring tools to do this.

In this chapter you will learn about:

• The big picture of the DB2 locking mechanism

• Different concurrency scenarios

• The DB2 isolation levels

• How DB2 isolation levels affect locking

• Troubleshooting tools that come with DB2 to identify locking problems

• Avoiding locking problems