1023. Find deadlock-friendly ordering — Hotel — implementation variant 23

DBMS Published 30 Sept 2026 Updated 30 Sept 2026 0 Views Verified

In a Hotel application, implement this production problem: Update two account rows without acquiring them in inconsistent order. The API/service receives user input and must return or modify data safely. Give the SQL solution, explain why it works, and show how the same operation is called from the selected stack.

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Answer & Explanation

4 Answers

Verified Correct Answer

Option A

START TRANSACTION; SELECT id FROM accounts WHERE id IN (:id1,:id2) ORDER BY id FOR UPDATE; UPDATE accounts SET balance=balance+:delta1 WHERE id=:id1; UPDATE accounts SET balance=balance+:delta2 WHERE id=:id2; COMMIT;

Additional Explanation

A consistent lock order reduces circular wait. Deadlocks can still occur and should be handled with retry logic.

Verified

Option B

SELECT * FROM the_table;

Additional Explanation

Incorrect: it does not implement the stated business rule and may modify/fetch the wrong rows.

Verified

Option C

UPDATE the_table SET status='active';

Additional Explanation

Incorrect: it does not implement the stated business rule and may modify/fetch the wrong rows.

Verified

Option D

DELETE FROM the_table;

Additional Explanation

Incorrect: it does not implement the stated business rule and may modify/fetch the wrong rows.