In the presumed commit version of the two-phase commit protocol described in the text, when the protocol starts, the coordinator forces a start record to its log. Describe a situation in which, if the coordinator had not forced this record to its log, the protocol would not work correctly.
What will be an ideal response?
The coordinator crashes during the first phase of the protocol after sending prepare messages to a number of the cohorts. Some of the cohorts that received the message have voted ready and some have voted aborting. After the coordinator crashes and is restarted, it finds no information about the transaction in its log. Later one of the cohorts that had voted ready (and had timed out while waiting for a response) asks
the coordinator the state of the transaction. Since the coordinator finds no transaction record for the transaction in its volatile memory, it reports, incorrectly, that the transaction has committed (some cohorts have already aborted).
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What will be an ideal response?