819 - 855: Data Layouts, OLTP/OLAP, In-Memory DBS

Question 1

What is the main feature of Conservative 2PL (C2PL)?
A. Locks are released at the end of transactions
B. All locks are requested before execution begins
C. Only write locks are used
D. Transactions are always serializable

Answer 1

B. All locks are requested before execution begins

Question 2

Explain the purpose of Two-Phase Locking (2PL).

Answer 2

2PL ensures CSR by dividing a transaction into two phases: a growing phase (acquiring locks) and a shrinking phase (releasing locks).

Question 3

What is Conservative 2PL (C2PL)?

Answer 3

In C2PL, a transaction requests all necessary locks upfront before execution, avoiding deadlocks but limiting practicality.

Question 4

What is Strict 2PL (S2PL)?

Answer 4

S2PL requires that all exclusive locks be held until the transaction commits or aborts, ensuring recoverable histories.

Question 5

Define Recoverable History.

Answer 5

A history is recoverable if a transaction only commits after all transactions it depends on have committed.

Question 6

What is ACA (Avoid Cascading Aborts)?

Answer 6

ACA ensures that no transaction reads uncommitted data, preventing cascading aborts.

Question 7

What is a strict history?

Answer 7

A history where transactions accessing modified data by others do so only after the modifying transaction has committed or aborted.

Question 8

What is the relationship between CSR, VSR, and FSR?

Answer 8

CSR ⊂ VSR ⊂ FSR, meaning CSR is the most restrictive and practical, while FSR is the least restrictive but not suitable for avoiding anomalies.

Question 9

What does the Serializability Theorem state?

Answer 9

A history belongs to CSR if and only if its conflict graph is acyclic.