24 Concurrency Control questions from the SQL bank, written for Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd.
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A.a write lock that only one transaction may hold and that blocks all other readers and writers on the resource
B.the engine's promotion of many fine-grained row locks into a single coarser table lock to reduce locking overhead
C.a read lock that several transactions may hold on the same resource at once but which blocks any writer
D.a technique that keeps multiple timestamped versions of a row so readers see a consistent snapshot without blocking writers
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2. Which term means: "a technique that keeps multiple timestamped versions of a row so readers see a consistent snapshot without blocking writers"?
Mid
A.Lock escalation
B.SAVEPOINT
C.Optimistic locking
D.MVCC
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3. Which statement is correct?
Mid
A.MVCC — a named marker within a transaction that lets you roll back part of the work without aborting the whole transaction
B.MVCC — the engine's promotion of many fine-grained row locks into a single coarser table lock to reduce locking overhead
C.MVCC — a technique that keeps multiple timestamped versions of a row so readers see a consistent snapshot without blocking writers
D.MVCC — a read lock that several transactions may hold on the same resource at once but which blocks any writer
Answer + AI explanation with Pro
4. What is Optimistic locking?
Senior
A.a strategy that assumes conflicts are rare and checks a version or timestamp only at commit time, retrying if the row changed
B.the engine's promotion of many fine-grained row locks into a single coarser table lock to reduce locking overhead
C.a write lock that only one transaction may hold and that blocks all other readers and writers on the resource
D.a strategy that acquires locks up front before reading or writing, blocking other transactions until they are released
Answer + AI explanation with Pro
5. Which term means: "a strategy that assumes conflicts are rare and checks a version or timestamp only at commit time, retrying if the row changed"?
Senior
A.Optimistic locking
B.MVCC
C.Shared lock
D.Two-phase locking
Answer + AI explanation with Pro
6. Which statement is correct?
Senior
A.Optimistic locking — a strategy that assumes conflicts are rare and checks a version or timestamp only at commit time, retrying if the row changed
B.Optimistic locking — a protocol with a growing phase that only acquires locks and a shrinking phase that only releases them, guaranteeing serializability
C.Optimistic locking — the engine's promotion of many fine-grained row locks into a single coarser table lock to reduce locking overhead
D.Optimistic locking — a named marker within a transaction that lets you roll back part of the work without aborting the whole transaction
Answer + AI explanation with Pro
7. What is Pessimistic locking?
Senior
A.a write lock that only one transaction may hold and that blocks all other readers and writers on the resource
B.a strategy that assumes conflicts are rare and checks a version or timestamp only at commit time, retrying if the row changed
C.a strategy that acquires locks up front before reading or writing, blocking other transactions until they are released
D.a protocol with a growing phase that only acquires locks and a shrinking phase that only releases them, guaranteeing serializability
Answer + AI explanation with Pro
8. Which term means: "a strategy that acquires locks up front before reading or writing, blocking other transactions until they are released"?
Senior
A.Two-phase locking
B.MVCC
C.Pessimistic locking
D.Lock escalation
Answer + AI explanation with Pro
9. Which statement is correct?
Senior
A.Pessimistic locking — a protocol with a growing phase that only acquires locks and a shrinking phase that only releases them, guaranteeing serializability
B.Pessimistic locking — a strategy that acquires locks up front before reading or writing, blocking other transactions until they are released
C.Pessimistic locking — a write lock that only one transaction may hold and that blocks all other readers and writers on the resource
D.Pessimistic locking — a named marker within a transaction that lets you roll back part of the work without aborting the whole transaction
Answer + AI explanation with Pro
10. What is Shared lock?
Mid
A.the engine's promotion of many fine-grained row locks into a single coarser table lock to reduce locking overhead
B.a read lock that several transactions may hold on the same resource at once but which blocks any writer
C.a write lock that only one transaction may hold and that blocks all other readers and writers on the resource
D.a protocol with a growing phase that only acquires locks and a shrinking phase that only releases them, guaranteeing serializability
Answer + AI explanation with Pro
11. Which term means: "a read lock that several transactions may hold on the same resource at once but which blocks any writer"?
Mid
A.Exclusive lock
B.Shared lock
C.MVCC
D.Pessimistic locking
Answer + AI explanation with Pro
12. Which statement is correct?
Mid
A.Shared lock — a strategy that acquires locks up front before reading or writing, blocking other transactions until they are released
B.Shared lock — a read lock that several transactions may hold on the same resource at once but which blocks any writer
C.Shared lock — the engine's promotion of many fine-grained row locks into a single coarser table lock to reduce locking overhead
D.Shared lock — a technique that keeps multiple timestamped versions of a row so readers see a consistent snapshot without blocking writers
Answer + AI explanation with Pro
13. What is Exclusive lock?
Mid
A.a protocol with a growing phase that only acquires locks and a shrinking phase that only releases them, guaranteeing serializability
B.a named marker within a transaction that lets you roll back part of the work without aborting the whole transaction
C.a read lock that several transactions may hold on the same resource at once but which blocks any writer
D.a write lock that only one transaction may hold and that blocks all other readers and writers on the resource
Answer + AI explanation with Pro
14. Which term means: "a write lock that only one transaction may hold and that blocks all other readers and writers on the resource"?
Mid
A.Optimistic locking
B.SAVEPOINT
C.Exclusive lock
D.MVCC
Answer + AI explanation with Pro
15. Which statement is correct?
Mid
A.Exclusive lock — a write lock that only one transaction may hold and that blocks all other readers and writers on the resource
B.Exclusive lock — the engine's promotion of many fine-grained row locks into a single coarser table lock to reduce locking overhead
C.Exclusive lock — a read lock that several transactions may hold on the same resource at once but which blocks any writer
D.Exclusive lock — a protocol with a growing phase that only acquires locks and a shrinking phase that only releases them, guaranteeing serializability
Answer + AI explanation with Pro
16. What is Lock escalation?
Senior
A.a named marker within a transaction that lets you roll back part of the work without aborting the whole transaction
B.a strategy that assumes conflicts are rare and checks a version or timestamp only at commit time, retrying if the row changed
C.the engine's promotion of many fine-grained row locks into a single coarser table lock to reduce locking overhead
D.a strategy that acquires locks up front before reading or writing, blocking other transactions until they are released
Answer + AI explanation with Pro
17. Which term means: "the engine's promotion of many fine-grained row locks into a single coarser table lock to reduce locking overhead"?
Senior
A.SAVEPOINT
B.Two-phase locking
C.Shared lock
D.Lock escalation
Answer + AI explanation with Pro
18. Which statement is correct?
Senior
A.Lock escalation — a strategy that assumes conflicts are rare and checks a version or timestamp only at commit time, retrying if the row changed
B.Lock escalation — the engine's promotion of many fine-grained row locks into a single coarser table lock to reduce locking overhead
C.Lock escalation — a read lock that several transactions may hold on the same resource at once but which blocks any writer
D.Lock escalation — a strategy that acquires locks up front before reading or writing, blocking other transactions until they are released
Answer + AI explanation with Pro
19. What is SAVEPOINT?
Mid
A.a named marker within a transaction that lets you roll back part of the work without aborting the whole transaction
B.a strategy that acquires locks up front before reading or writing, blocking other transactions until they are released
C.a strategy that assumes conflicts are rare and checks a version or timestamp only at commit time, retrying if the row changed
D.the engine's promotion of many fine-grained row locks into a single coarser table lock to reduce locking overhead
Answer + AI explanation with Pro
20. Which term means: "a named marker within a transaction that lets you roll back part of the work without aborting the whole transaction"?
Mid
A.Shared lock
B.Optimistic locking
C.Lock escalation
D.SAVEPOINT
Answer + AI explanation with Pro
21. Which statement is correct?
Mid
A.SAVEPOINT — a named marker within a transaction that lets you roll back part of the work without aborting the whole transaction
B.SAVEPOINT — a protocol with a growing phase that only acquires locks and a shrinking phase that only releases them, guaranteeing serializability
C.SAVEPOINT — a strategy that acquires locks up front before reading or writing, blocking other transactions until they are released
D.SAVEPOINT — the engine's promotion of many fine-grained row locks into a single coarser table lock to reduce locking overhead
Answer + AI explanation with Pro
22. What is Two-phase locking?
Senior
A.a write lock that only one transaction may hold and that blocks all other readers and writers on the resource
B.a named marker within a transaction that lets you roll back part of the work without aborting the whole transaction
C.a protocol with a growing phase that only acquires locks and a shrinking phase that only releases them, guaranteeing serializability
D.a technique that keeps multiple timestamped versions of a row so readers see a consistent snapshot without blocking writers
Answer + AI explanation with Pro
23. Which term means: "a protocol with a growing phase that only acquires locks and a shrinking phase that only releases them, guaranteeing serializability"?
Senior
A.Lock escalation
B.Two-phase locking
C.Shared lock
D.Optimistic locking
Answer + AI explanation with Pro
24. Which statement is correct?
Senior
A.Two-phase locking — a write lock that only one transaction may hold and that blocks all other readers and writers on the resource
B.Two-phase locking — a strategy that assumes conflicts are rare and checks a version or timestamp only at commit time, retrying if the row changed
C.Two-phase locking — a named marker within a transaction that lets you roll back part of the work without aborting the whole transaction
D.Two-phase locking — a protocol with a growing phase that only acquires locks and a shrinking phase that only releases them, guaranteeing serializability
Answer + AI explanation with Pro
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