A three-phase commit protocol has the following parts : Phase 1: is the same as

Question

A three-phase commit protocol has the following parts

: Phase 1: is the same as for two-phase commi

t. Phase 2: the coordinator collects the votes and makes a decision; if it is No, it aborts and informs participants that voted Yes; if the decision is Yes, it sends a preCommit request to all the participants. participants that voted Yes wait for a preCommit or doAbort request. They acknowledge preCommit requests and carry out doAbort requests.

Phase 3: the coordinator collects the acknowledgments. When all are received, it Commits and sends doCommit to the participants. participants wait for a doCommit request. When it arrives they Commit. Explain how this protocol avoids delay to participants during their uncertain period due to the failure of the coordinator or other participants. Assume that communication does not fail.

Explanation / Answer

Comming to the second phase:
In the two-phase commit protocol:
The ‘uncertain’ period occurs because a worker has voted yes but has not yet been told the outcome.
Moving on to the third phase

In the three-phase commit protocol:
The workers ‘uncertain’ period lasts from when the worker votes yes until it receives the PreCommit request.
At this point no other participant can have committed.
If a group of workers discover that they are all ‘uncertain’ and the coordinator cannot be contacted, they can decide unilaterally to abort

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