Some distributed transaction mechanisms, such as X/Open-XA protocols, are not connection-oriented, and allow applications to issue commands on different connections. As a result, requests to resume work on a suspended transaction branch can be issued on a nonowner instance. Likewise, requests for commit processing can be issued on a connection to a nonowner instance. In a clustered Adaptive Server, such requests issued on nonowner instances require special processing.
When a request is issued on a nonowner instance, the clustered Adaptive Server determines the owner instance for the transaction, and then migrates the connection to the owner instance with the help of the connectivity libraries. The connection migration is transparent to the application. After a successful connection migration, the request is processed on the owner instance.
See Chapter 2, “Client Applications and Client/ Server Interaction,” for more information about connection migration.
ASTC transactions do not need connection migration. The ASTC mechanism requires that all Transact-SQL statements and the commit processing for transactions are issued on the same connection.
