DB2® Universal Database for OS/390® Version 7.1 Certification Guide

Chapter 14. Locking and Concurrency

• Locking Data

• Lock Attributes

• Avoiding Locks

• Claims and Drains

• Escalation and Promotion

It would be easy to have one process simply lock all the data while using it, but that, of course, would lead to other applications being unable to access the data during this time. Concurrency, the ability for multiple applications to access the same data at the same time, needs to be allowed but also controlled so that we prevent lost updates, access to uncommitted data, or have unrepeatable reads (data changing between reads).

A balance must be achieved for best concurrency of all processes. There are many controls in DB2 to allow it to achieve maximum concurrency while maintaining the integrity of our data. This ranges from ...