Multi Step Processes hard
In the Two-Phase Commit protocol (2PC), what happens if the Coordinator crashes *after* sending 'Prepare' but *before* sending 'Commit'?
- A The transaction commits automatically.
- B The participants automatically rollback after 1 second.
- C The participants remain in a 'Blocked' state, holding locks indefinitely, waiting for the Coordinator to recover and tell them the outcome.
- D The participants elect a new leader.
Answer: C. The participants remain in a 'Blocked' state, holding locks indefinitely, waiting for the Coordinator to recover and tell them the outcome.
This is the 'Blocking' nature of 2PC. The participants voted 'Yes' and are now waiting for the final instruction. They cannot abort (maybe others committed) and cannot commit (maybe others aborted). They are stuck.
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