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Subject: Issue - 16 - Ensuring exactly once


This issue has been added to the wsbpel issue list. It is in the current version of the list at wsbpel document 2656, It is hoped to have a fixed url for the ever-changing list.

Issue - 16 - Ensuring exactly once

Origin: Extracted from email Mike Marin, 22 May 2003 - issue "a" from that message
Date submitted: 22 May 2003
Submitter: Mike Marin, Filenet
Description:
We don't have distributed transactions on web services yet. So how do we insure that an activity such as an "invoke" is executed exactly one time? The following example illustrates the problem: 1. Process A begins execution of an invoke instruction, and sends an input message to Process B. There is no output message defined on the invoke.

2. Process B is defined with a receive instruction corresponding to the invoke of process A, and the receive instruction creates a new instance of the process. So upon receipt of the message from process A, a new instance of process B is created, and this instance executes the receive instruction.

3. The machine hosting process A crashes.

4. Process B executes the next step, which is to debit an account and update a database.

5. Process B terminates. Process B has finished.

6. The machine hosting process A is restarted. Process A then re-executes the invoke instruction. On step 6, how can we prevent process A from executing the invoke a second time, creating another instance of process B, and debiting the account a second time?


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