GATE CSE 2020 Q47: Schedule conflict equivalent to a given two-transaction schedule

Databases
2 marks
MCQ
−2/3 if wrong

Consider a schedule of transactions $T_1$ and $T_2$ (time runs left to right):

Given schedule
$T_1$	RA			RC		WD		WB	Commit
$T_2$		RB	WB		RD		WC			Commit

Schedule (A)
$T_1$				RA	RC	WD	WB		Commit
$T_2$	RB	WB	RD					WC		Commit

Schedule (B)
$T_1$	RA	RC	WD	WB					Commit
$T_2$					RB	WB	RD	WC		Commit

Schedule (C)
$T_1$	RA	RC	WD				WB		Commit
$T_2$				RB	WB	RD		WC		Commit

Schedule (D)
$T_1$					RA	RC	WD	WB	Commit
$T_2$	RB	WB	RD	WC						Commit

Here, RX stands for "Read(X)" and WX stands for "Write(X)". Which one of the following schedules is conflict equivalent to the above schedule?

Try it: multiple choice: exactly one correct option

Wrong answer costs 2/3 mark in GATE.

Show answer and explanation

Answer: A (official GATE 2020 final answer key)

Concept used: Two schedules are conflict equivalent if every pair of conflicting operations appears in the same order in both.

First step: List the conflicting pairs in the given schedule: $T_2$ 's RB and WB before $T_1$ 's WB, $T_2$ 's RD before $T_1$ 's WD, and $T_1$ 's RC before $T_2$ 's WC. Check each option against them.

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Source: official GATE 2020 CS question paper and final answer key, organised by IIT Delhi. Question paper · Answer key

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GATE CSE 2020 Q47: Schedule conflict equivalent to a given two-transaction schedule

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