Programming Microsoft® SQL Server® 2012

Isolation Levels

As we’ve started explaining, the isolation behavior of a transaction can be tweaked to your needs. This is generally done by setting the isolation level of a transaction. Put simply, isolation levels determine how concurrent transactions behave. Do they block each other? Do they let each other step over themselves? Or do they present a snapshot of a previous stable state of data in the event of an overstepped condition?

You can set isolation levels by using the SET TRANSACTION ISOLATION LEVEL statement, which uses the following syntax:

SET TRANSACTION ISOLATION LEVEL
    { READ UNCOMMITTED
    | READ COMMITTED
    | REPEATABLE READ
    | SNAPSHOT
    | SERIALIZABLE
    }

A sample usage of this statement with the BEGIN TRANSACTION statement is shown here: ...