GATE CS 2017 Set 2 — Question 44
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Databases → Transactions & Concurrency → Conflict Serializability
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Question
Two transactions and are given as
where denotes a read operation by transaction on a variable and denotes a write operation by transaction on a variable . The total number of conflict serializable schedules that can be formed by and is ________.
where denotes a read operation by transaction on a variable and denotes a write operation by transaction on a variable . The total number of conflict serializable schedules that can be formed by and is ________.
Correct answer
54 to 54
Solution
A schedule is conflict serializable if it is conflict equivalent to a serial schedule. For two transactions and , the possible serial orders are and .Conflicts between and occur on variable :
1.Equivalent to : Requires all conflicting operations of to precede those of . Specifically, , which means . This only happens in 1 schedule: .
2.Equivalent to : Requires all conflicting operations of to precede those of . Specifically, , which means .
Total possible schedules = . We count schedules where (at least two operations appear before the third operation). Using combinatorics, the number of such schedules is 53.Total conflict serializable schedules = .Continue learning with Success Tracker
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