Microsoft® SQL Server 2012 Unleashed

READ_COMMITTED_SNAPSHOT Isolation

In addition to the SNAPSHOT isolation level, SQL Server also supports a special form of read-committed isolation, referred to as READ_COMMITTED_SNAPSHOT. This form of isolation is similar to snapshot isolation, but unlike snapshot isolation, which sees the version of the data at the start of the transaction, read committed snapshot queries see the version of the data at the start of the statement.

To enable the READ_COMMITTED_SNAPSHOT isolation level for queries, you need to enable the READ_COMMITTED_SNAPSHOT database option. Any queries that normally would run at the standard READ_COMMITTED isolation level automatically run at the READ_COMMITTED_SNAPSHOT isolation level without requiring any code changes.