Connection level isolation in a federated system

For each connection to the data source, the wrapper determines the isolation level.

When the federated server connects to the data source, the isolation level at the remote data source is set to a level that is equivalent to the level of the federated server. If there is no exact equivalent, then the federated server sets the isolation level to the next restrictive level. After a connection is made to a data source, the isolation level for the duration of the connection cannot be changed.

All wrappers except Teradata keep track of the connection isolation level. When setting up a connection, the wrappers set the connection isolation level to the equivalent of the current isolation level. The current isolation level is the isolation level of the current section (first federated statement to a data source). The Teradata wrapper is always in the READ isolation level, the default, because the Teradata wrapper does not have a way to change the connection isolation level.