781 - 818: Probabilistic Databases

Question 1

Explain the difference between physical and logical logging.

Answer 1

Physical Logging: Logs the exact before and after images of data.
Logical Logging: Logs operations (e.g., x += 10) rather than the exact changes, requiring a consistent database state for application.

Question 2

What is the function of a buffer in database management?

Answer 2

The buffer temporarily stores data pages in memory, reducing disk I/O by enabling operations to occur in memory.

Question 3

What is a schedule in database systems?
A. A sequence of unrelated transactions
B. A sequence of operations from a set of transactions
C. A list of aborted transactions
D. A history of failed executions

Answer 3

B. A sequence of operations from a set of transactions

Question 4

Which anomaly occurs when two transactions write conflicting values without proper synchronization?
A. Dirty Read
B. Lost Update
C. Inconsistent Read
D. Phantom Read

Answer 4

B. Lost Update

Question 5

What does FSR (Final State Serializability) guarantee?
A. Transactions will commit in a specific order
B. The final state matches that of a serial execution
C. No cascading aborts will occur
D. Conflicts are resolved using locking

Answer 5

B. The final state matches that of a serial execution

Question 6

Which class of schedules is guaranteed to avoid anomalies like dirty reads and cascading aborts?
A. CSR
B. VSR
C. Strict Histories
D. OCSR

Answer 6

C. Strict Histories

Question 7

What is a strict history?
A. A history where all transactions follow VSR
B. A history where locks are held until commit or abort
C. A history that prohibits multiple transactions on the same data
D. A history that matches its prefix to a serializable one

Answer 7

B. A history where locks are held until commit or abort

Question 8

Define Lost Update Anomaly.

Answer 8

Two transactions read the same value and update it independently, resulting in the loss of one update.

Question 9

What is Inconsistent Read Anomaly?

Answer 9

A transaction reads values that are being modified by another transaction, leading to inconsistent or partial results

Question 10

What is Dirty Read Anomaly?

Answer 10

A transaction reads a value written by another transaction that has not yet committed, leading to potential inconsistency if the writing transaction is rolled back.

Question 11

Define Final State Serializability (FSR).

Answer 11

FSR ensures that the final state of the database matches that of a serial execution, starting from the same initial state.

Question 12

What is View Serializability (VSR)?

Answer 12

VSR ensures that every transaction reads values as if it were executed in a serial order, avoiding inconsistent reads.

Question 13

What is Conflict Serializability (CSR)?

Answer 13

CSR ensures serializability by resolving conflicts using a conflict graph, which must remain acyclic.