SQL Server Isolation Levels : A Series

Photo Credit : Alexander Baxevanis

Updated April 23, 2015

Last year, I put together a string of posts aimed at taking a detailed look at concurrency, the ACID properties of statements and transactions, and each of the major isolation levels in SQL Server. Now I have concluded the series with a final post on probably the most common intentionally-used isolation level: read uncommitted ("NOLOCK").

Since you've been patient for the final installment, there is some other background reading/watching on read uncommitted that I can offer:

• Lubor Kollar : Previously committed rows might be missed if NOLOCK hint is used
• Aaron Bertrand : Bad Habits : Putting NOLOCK Everywhere
• Craig Freedman : Query Failure with Read Uncommitted
• Aaron Bertrand : Avoid using NOLOCK on SQL Server UPDATE and DELETE statements
• David Lean : SQL Server NOLOCK Hint & other poor ideas
• Sunil Agarwal : Concurrency Series: Why do I get blocking when I use Read Uncommitted isolation level or use NOLOCK hint?
• Tony Rogerson : Timebomb – The Consistency Problem with NOLOCK / READ UNCOMMITTED (and a follow-up)