SQL Server Isolation Levels : A Series

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").

The ACID Properties of Statements & Transactions

The Serializable Isolation Level

The Repeatable Read Isolation Level

The Read Committed Isolation Level

Read Committed Snapshot Isolation

Data Modifications under Read Committed Snapshot Isolation

The SNAPSHOT Isolation Level

The Read Uncommitted Isolation Level

 

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)