## Friday, 27 August 2021

### Concurrency Control Protocols

If a transaction has obtained a __________ lock, it can read but cannot write on the item
a) Shared mode
b) Exclusive mode
d) Write only mode

If a transaction has obtained a ________ lock, it can both read and write on the item
a) Shared mode
b) Exclusive mode
d) Write only mode

A transaction can proceed only after the concurrency control manager ________ the lock to the transaction
a) Grants
b) Requests
c) Allocates
d) None of the mentioned

If a transaction can be granted a lock on an item immediately in spite of the presence of another mode, then the two modes are said to be ________
a) Concurrent
b) Equivalent
c) Compatible
d) Executable

A transaction is made to wait until all ________ locks held on the item are released
a) Compatible
b) Incompatible
c) Concurrent
d) Equivalent

The situation where no transaction can proceed with normal execution is known as ________
c) Execution halt
d) Abortion

The protocol that indicates when a transaction may lock and unlock each of the data items is called as __________
a) Locking protocol
b) Unlocking protocol
c) Granting protocol
d) Conflict protocol

The two phase locking protocol consists which of the following phases?
a) Growing phase
b) Shrinking phase
c) Both a and b
d) None of the mentioned

If a transaction may obtain locks but may not release any locks then it is in _______ phase
a) Growing phase
b) Shrinking phase
d) Starved phase

If a transaction may release locks but may not obtain any locks, it is said to be in ______ phase
a) Growing phase
b) Shrinking phase
d) Starved phase

Which of the following cannot be used to implement a timestamp
a) System clock
b) Logical counter
c) External time counter
d) None of the mentioned

A logical counter is _________ after a new timestamp has been assigned
a) Incremented
b) Decremented
c) Doubled
d) Remains the same

The _________ requires each transaction executes in two or three different phases in its lifetime
a) Validation protocol
b) Timestamp protocol
d) View protocol

During __________ phase, the system reads data and stores them in variables local to the transaction.
b) Validation phase
c) Write phase
d) None of the mentioned

During the _________ phase the validation test is applied to the transaction
b) Validation phase
c) Write phase
d) None of the mentioned

During the _______ phase, the local variables that hold the write operations are copied to the database
b) Validation phase
c) Write phase
d) None of the mentioned

Read only operations omit the _______ phase
b) Validation phase
c) Write phase
d) None of the mentioned

## Friday, 20 August 2021

### Conflict Serializability Assignment - S P SHARMA CLASSES

Question : Consider the following schedules involving two transactions. Which one of the following statement is true?

S1: R1(X) R1(Y) R2(X) R2(Y) W2(Y) W1(X)
S2: R1(X) R2(X) R2(Y) W2(Y) R1(Y) W1(X)

• Both S1 and S2 are conflict serializable
• Only S1 is conflict serializable
• Only S2 is conflict serializable
• None

Question 2 : Consider the following schedules involving two transactions. Which one of the following statement is true?

S1: r1(x) r1(y) w2(x) w1(x) r2(y)
S2: r1(x) r3(y) w1(x) w2(y) r3(x) w2(x)

• Both S1 and S2 are conflict serializable
• Only S1 is conflict serializable
• Only S2 is conflict serializable
• None
Question 3 : Consider the following schedules involving three transactions. Which one of the following statement is true?
S1: r1(X); r3(Y); r3(X); r2(Y); r2(Z);
w3(Y); w2(Z); r1(Z); w1(X); w1(Z)
S2: r1(X); r3(Y); r2(Y); r3(X); r1(Z);
r2(Z); w3(Y); w1(X); w2(Z); w1(Z) 

Which one of the following statements about the schedules is TRUE?
(A) Only S1 is conflict-serializable.
(B) Only S2 is conflict-serializable.
(C) Both S1 and S2 are conflict-serializable.
(D) Neither S1 nor S2 is conflict-serializable.

Question 4 : Let $S$ be the following schedule of operations of three transactions  and  in a relational database system:



Consider the statements $P$ and $Q$ below:

•  is conflict-serializable.
• : If  commits before  finishes, then  is recoverable.

Which one of the following choices is correct?

1. Both  and are true
2.  is true and  is false
3.  is false and  is true
4. Both  and  are false

1. C
2. C
3. A
4. B