Code AnalysisHard 60s

Lost update from read-modify-write

Final balance is 150 instead of 180. This is:

Starter code

-- T1 and T2 run concurrently
SELECT balance FROM accounts WHERE id=1;  -- both read 100
UPDATE accounts SET balance = 100 + 50 WHERE id=1;
UPDATE accounts SET balance = 100 + 30 WHERE id=1;

transactions lost-update concurrency

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