Questions / Quant development, Streaming market data
Recover a prepared sink transaction
A toy sink writes output into transaction T and durably checkpoints T’s identity plus the input cursor before acknowledging checkpoint completion. It then crashes before learning whether commit(T) succeeded. What property is needed for safe recovery?
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Answer: D. Resolve transaction T and retry its commit idempotently.
- The durable checkpoint links an input cursor to transaction T.
- After the crash, T may already be committed even though the client did not learn that fact.
- Query or retry the same transaction identity so recovery converges on one output commit.
Interview shortcut. Two-phase sink: resolve T and commit idempotently.
Takeaway. Ambiguous commit outcomes require stable transaction identities.
Why the other choices fail
- Open a new transaction for the same output. A new transaction can duplicate T if T already committed.
- Create fresh output when commit status is unknown. A fresh transaction can duplicate output if T already committed.
- Treat the lost acknowledgment as an abort, then re-emit. An absent acknowledgment does not establish an absent remote commit.
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