Remote unit of work
The remote unit of work facility provides for the remote preparation and execution of SQL statements. An activation group at computer system A can connect to an application server at computer system B. Then, within one or more units of work, that activation group can execute any number of static or dynamic SQL statements that reference objects at B. After ending a unit of work at B, the activation group can connect to an application server at computer system C, and so on.
Most SQL statements can be remotely prepared and executed with the following restrictions:
- All objects referenced in a single SQL statement must be managed by the same application server.
- All of the SQL statements in a unit of work must be executed by the same application server.
Remote unit of work connection management
An activation group is in one of three states at any time:
- Connectable and connected
- Unconnectable and connected
- Connectable and unconnected
The following diagram shows the state transitions:
The initial state of an activation group is connectable and connected.
The connectable and connected state
An activation group is connected to an application server and CONNECT statements can be executed. The activation group enters this state when it completes a rollback or successful commit from the unconnectable and connected state, or a CONNECT statement is successfully executed from the connectable and unconnected state.
The unconnectable and connected state
An activation group is connected to an application server, but a CONNECT statement cannot be successfully executed to change application servers. The activation group enters this state from the connectable and connected state when it executes any SQL statement other than CONNECT, COMMIT, or ROLLBACK.
The connectable and unconnected state
An activation group is not connected to an application server. The only SQL statement that can be executed is CONNECT.
The activation group enters this state when:
- The connection was previously released and a successful COMMIT is executed.
- The connection is disconnected using the SQL DISCONNECT statement.
- The connection was in a connectable state, but the CONNECT statement was unsuccessful.
Consecutive CONNECT statements can be executed successfully because CONNECT does not remove the activation group from the connectable state. A CONNECT to the application server to which the activation group is currently connected is executed like any other CONNECT statement. CONNECT cannot execute successfully when it is preceded by any SQL statement other than CONNECT, COMMIT, DISCONNECT, SET CONNECTION, RELEASE, or ROLLBACK (unless running with COMMIT(*NC)). To avoid an error, execute a commit or rollback operation before a CONNECT statement is executed.