Presumed-end optimization

Presumed-end optimization is a term that describes how the two-phase commit protocol handles the rollback of a transaction.

Rollback is handled in the following manner. When the coordinator determines that the transaction must be rolled back, it sends a message to all the participants to roll back their piece of work. The coordinator does not wait for an acknowledgment of this message, but proceeds to close the transaction and remove it from shared memory. If a participant tries to determine the status of this transaction—that is, find out whether the transaction was committed or rolled back (during participant recovery, for example)—it does not find any transaction status in shared memory. The participant must interpret this as meaning that the transaction was rolled back.


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