The following diagram illustrates the communications that take place during a typical two-phase commit operation involving three systems. In this example, A is the coordinator since it initiates the commit operation, and B and C are participants.
In this example, A forwards a Prepare request to each of its participants, directing them to prepare for a commit. After B and C both respond positively, A then directs them to complete the commit operation.
The following diagram illustrates another typical commit flow. In this example, A is again the overall transaction coordinator, and B and C are participants. However, in this case, B plays a dual role. It is both a participant with respect to A and a coordinator with respect to C since it forwards the Prepare and Commit directives that it receives from A to C. Such a situation might arise because an application on A starts a remote SQL session on B that, in turn, updates resources on C through an SQL procedure.
|
Copyright © 2014 CA.
All rights reserved.
|
|