Isolation Levels

This section discusses the isolation levels supported by SequeLink.

Table B-8 lists the isolation levels supported by each data store, including their default isolation level.

Table B-8. Isolation Levels 

Database	Isolation Levels	Default
DB2 UDB on z/OS	Read uncommitted Read committed Repeatable read Serializable	Read committed
DB2 UDB on Linux/UNIX/Windows	Read uncommitted Read committed Repeatable read Serializable	Read committed
Informix	Read uncommitted Read committed Repeatable read	Read committed
Microsoft SQL Server	Read uncommitted Read committed Read Committed with Snapshots1 Read Committed with Locks1 Repeatable read Serializable Snapshot1	Read committed
Oracle	Read committed Serializable	Read committed
Sybase	Read uncommitted Read committed Repeatable read Serializable	Read committed

1Supported on Microsoft SQL Server only. See "Using Snapshot Isolation Level (Microsoft SQL Server 2005 Only)" for more information.

Using Snapshot Isolation Level (Microsoft SQL Server 2005 Only)

The Snapshot isolation level is available only with Microsoft SQL Server 2005. Enabling the SnapshotSerializable connection option changes the behavior of the Serializable isolation level to use the Snapshot Isolation level. This allows an application to use the Snapshot Isolation level with no or minimum code changes.

To configure Snapshot Isolation for connections, you must have your Microsoft SQL Server 2005 database configured for Snapshot Isolation and your application must have the transaction isolation level set to Serializable.

See the following sections for the connection information specific to the SequeLink Client.

Using The Snapshot Isolation Level with the ODBC Driver

If you are writing a new application, you may want to code it to set the connection attribute SQL_COPT_SS_TXN_ISOLATION to the value SQL_TXN_SS_SNAPSHOT. The application then uses the snapshot isolation level without requiring the Use Snapshot Transactions connection option.