Microsoft® SQL Server™ 2005 Administrator's Companion

Isolation Levels

SQL Server 2005 supports five isolation levels that affect the way locking behavior for read operations is handled. There is one new isolation level and one new option to an existing isolation level for SQL Server 2005 that are intended to enhance concurrency for online transaction processing (OLTP) applications: snapshot isolation and read committed snapshot. These depend on a new feature called row versioning that can be used to avoid reader-writer blocking scenarios.

The transaction isolation level determines the level at which a transaction is allowed to read inconsistent data—that is, the degree to which one transaction is isolated from another. A higher isolation level increases data accuracy, but it can reduce the number ...