Microsoft® SQL Server® 2008 Internals

Chapter 10. Transactions and Concurrency

Kalen Delaney

Concurrency can be defined as the ability of multiple processes to access or change shared data at the same time. The greater the number of concurrent user processes that can be active without interfering with each other, the greater the concurrency of the database system.

Concurrency is reduced when a process that is changing data prevents other processes from reading that data or when a process that is reading data prevents other processes from changing that data. I use the terms reading or accessing to describe the impact of using the SELECT statement on your data. Concurrency is also affected when multiple processes attempt to change the same data simultaneously and they cannot all succeed ...