ISRO CSE 2018 PYQ ⋆ CSE Study247

Question 76

MCQ · Single Correct 1 mark

Previous Year Question ISRO CSE 2018 PYQ

Let us assume that transaction T1 has arrived before transaction T2. Consider schedule ?

CODE

S=r1(A); r2(B) ; w2(A) ; w1(B)
Which of the following is true?

A Allowed under basic timestamp protocol. B Not allowed under basic timestamp protocols because T1 is rolled Back. C Not allowed under basic timestamp protocols because T2 is rolled back, D None of these

📘 Solution & Detailed Explanation

🔢 Step-by-Step Solution

Step-by-Step Explanation

Understand the Setup & Core Rules

Since transaction $T_{1}$ arrives before transaction $T_{2}$, their timestamps ($TS$) are ordered as:
$TS(T_{1}) Let's assign simple numerical values to illustrate:
• \(TS(T_1) = 10$
• $TS(T_2) = 20$
Initially, the Read Timestamp ($R\_TS$) and Write Timestamp ($W\_TS$) for both data items $A$ and $B$ are set to 0.

Protocol Rules for Basic Timestamp Ordering (TO)

CODE

• For a Read operation r_i(X):
	• If \(TS(T_i) < W\_TS(X)\), then \(T_{i}\) is rolled back.
	• Otherwise, the read is allowed, and \(R\_TS(X) = \max(R\_TS(X), TS(T_i))\).
• For a Write operation w_i(X):
	• If \(TS(T_i) < R\_TS(X)\) or \(TS(T_i) < W\_TS(X)\), then \(T_{i}\) is rolled back.
	• Otherwise, the write is allowed, and \(W\_TS(X) = TS(T_i)\).

Trace the Schedule $S = r_1(A); r_2(B); w_2(A); w_1(B)$

CODE

\(r_1(A)\): \(T_{1}\) reads \(A\)
	• Check: \(TS(T_1) = 10 \ge W\_TS(A) = 0\) (Allowed)
	• Update: \(R\_TS(A) = \max(0, 10) = \mathbf{10}\)

CODE

\(r_2(B)\): \(T_{2}\) reads \(B\)
	• Check: \(TS(T_2) = 20 \ge W\_TS(B) = 0\) (Allowed)
	• Update: \(R\_TS(B) = \max(0, 20) = \mathbf{20}\)

CODE

\(w_2(A)\): \(T_{2}\) writes \(A\)
	• Check: \(TS(T_2) = 20 \ge R\_TS(A) = 10\) and \(TS(T_2) = 20 \ge W\_TS(A) = 0\) (Allowed)
	• Update: \(W\_TS(A) = \mathbf{20}\)

CODE

\(w_1(B)\): \(T_{1}\) writes \(B\)
	• Check: Compare \(TS(T_1)\) against \(R\_TS(B)\)
	• Since \(TS(T_1) = 10 < R\_TS(B) = 20\), this violates the protocol. \(T_{1}\) is attempting to write an older value into a data item that has already been read by a newer transaction (\(T_{2}\)).

Conclusion

Because of the protocol violation at step 4, $T_{1}$ is rejected and rolled back, making Option B the correct statement.

Question 77

MCQ · Single Correct 1 mark

Previous Year Question ISRO CSE 2018 PYQ

The time complexity of computing the transitive closure of binary relation on a set of n elements is known to be

A O ( n ) B $O ( n * \log( n ) )$ C $O ( n ^{3/2} )$ D O ( n ^ 3 )

Question 78

MCQ · Single Correct 1 mark

Previous Year Question ISRO CSE 2018 PYQ

in multi-programmed systems, it is advantageous if some programs such as editors and compilers can be shared by several users.
Which of the following must be true of multi-programmed systems in order that a single copy of a program can be shared by several
users?
I. The program is a macro
II. The program is recursive
III. The program is reentrant

A I only B II only C III only D I, II and III

Question 79

MCQ · Single Correct 1 mark

Previous Year Question ISRO CSE 2018 PYQ

Let P be a procedure that for some inputs calls itself ( i.e. is recursive ). If P is guaranteed to terminate, which of the following
statement(s) must br true?
I. Phas local variable
II. Phas an execution path whereit does notcall itself
III. P either refers to a global variable or has at least one parameter

A I only B II only III only C III only D II only

Question 80

MCQ · Single Correct 1 mark

Previous Year Question ISRO CSE 2018 PYQ

Consider the following C program

#include <stdio.h>
main()
{
float sum = 0.0, j = 1.0, i = 2.0;
while ( i/j > 0.001 ){
j=i+1
sum = sum + i/j;
printf ( “%f
”, sum);
}
}
How many lines of output does this program produce?

A 0-9 lines of output B 10-19 lines out output C 20-29 lines of output D More than 29 lines of output