prepare
phase are allowed to make autonomous decisions about whether to commit or rollback. Such a participant must record its decision, so that it can complete the original transaction if it eventually gets a request to do so. If the coordinator eventually informs the participant of the transaction outcome, and it is the same as the choice the participant made, no conflict exists. If the decisions of the participant and coordinator are different, the situation is referred to as a non-atomic outcome, and more specifically as a heuristic outcome.
Outcome
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Description
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Heuristic Rollback
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The commit operation failed because some or all of the participants unilaterally rolled back the transaction.
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Heuristic Commit
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An attempted rollback operation failed because all of the participants unilaterally committed. One situation where this might happen is if the coordinator is able to successfully
prepare the transaction, but then decides to roll it back because its transaction log could not be updated. While the coordinator is making its decision, the participants decides to commit.
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Heuristic Mixed
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Some participants commit ed, while others were rolled back.
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Heuristic Hazard
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The disposition of some of the updates is unknown. For those which are known, they have either all been committed or all rolled back.
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