Databases · Transactions and Concurrency Control
Official IIT answer key · IIT Delhi · Audited Aug 2026
GATE CSE 2012 Q27 · MCQ · 2 marks
read (P);read (Q);if P = 0 then Q := Q + 1 ;write (Q).
T2 : read (Q);read (P);if Q = 0 then P := P + 1 ;write (P).
Any non-serial interleaving of T1 and T2 for concurrent execution leads toKey concept
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Topic notes
Across 2012–2026, Transactions and Concurrency Control in GATE CS is heavily weighted towards testing precedence (serialization) graphs for conflict serializability, schedule classification (recoverable, cascadeless, strict), and locking/timestamping protocol mechanics. Questions frequently present interleaved schedules and require students to identify conflict edges, count valid topological orders, or detect recovery anomalies such as dirty reads and cascading rollbacks. Recent exams (2021–2025) feature multiple MSQs testing theoretical invariants of Two-Phase Locking (2PL), deadlock prevention protocols (Wait-Die, Wound-Wait), and real-world ACID violations.
Full Transactions and Concurrency Control guide →Consider the following transactions with data items P and Q initialized to zero: T1 : read (P); read (Q); if P = 0 then Q := Q + 1 ; write (Q). T2 : read (Q); read (P); if Q = 0 then P := P + 1 ; write (P). Any non-serial interleaving of T1 and T2 for concurrent execution leads to
Topic-wise GATE CS PYQs with verified steps
Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.