Within a DBMS, what are the core responsibilities of a Transaction Manager (consider logging, recovery, and concurrency)?
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AMaintains a log of transactions
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BMaintains before and after database images
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CMaintains appropriate concurrency control
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DAll of the above.
Answer
Correct Answer: All of the above.
Explanation
Introduction / Context:The transaction manager enforces ACID properties in database systems. It coordinates logging, recovery, and isolation so that committed work is durable and concurrent activities do not corrupt data.
Given Data / Assumptions:
- Transactions need atomicity and durability (logging, recovery).
- Isolation requires concurrency control (locks, MVCC).
- System failures must be recoverable using logs and images.
Concept / Approach:A transaction manager typically maintains a transaction log, stores before/after images (or logical redo/undo information), and enforces concurrency control via locking or MVCC to achieve isolation levels.
Step-by-Step Solution:
Map ACID properties to mechanisms: A/D → logging & images; I → concurrency control.Recognize the transaction manager as the component integrating these functions.Select the option that includes all duties.Verification / Alternative check:DBMS architecture references consistently list logging/recovery and locking/MVCC under the transaction subsystem.
Why Other Options Are Wrong:
- A/B/C alone are partial; D captures the complete set.
Common Pitfalls:Believing logging alone guarantees isolation; without concurrency control, anomalies can occur.
Final Answer:All of the above.