# Recent questions tagged transactions

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Which of the following protocols does not ensure conflict serializability and safety from deadlocks? Graph based protocols Two-phase locking protocol Time-stamp ordering protocol Both a & b
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Two transactions T1 and T2 are given as follows: T1: R1(A) W1(A) R1(B) W1(B) T2: R2(B) W2(B) R2(C) W2(C) The total number of conflicts serializable schedules that can be formed by T1 and T2 are:
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The schedule is given below. Find out the category of the schedule S: R1(X),R2(Z)R1(Z),R3(X) W1(X) W3(Y) R2(Y) W2(Z) W2(Y) C1 C2 C3 Recoverable schedule Conflict Serializable Strict schedule None of these
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The time stamp of two transactions T1 and T2 are 10 and 15 respectively. Consider the following schedule with T1 and T2 operations. S1:r1(x),w1(x),r2(x),w2(x),r1(y),w1(y),r2(y),w2(y) Find the schedules? S is serializable using basic timestamp protocol S is serializable using basic Thomas write rule S is serializable using basic multiversion timestamp All of these
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(TS: time stamp) If TS (T) < Read-TS (Q), then write is rejected and T is rolled back If TS (T) < write-TS (Q), then write is rejected and T is rolled back Both (A) and (B) None of these
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Why is this schedule not allowed under strict two phase locking?
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Wait die is non preemptive technique :So cannot suffer from starvation. Wound wait is preemptive technique : is it suffers from starvation? i think yes but not sure plz explain with some example:
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1. How many super key is possible if (a,bc,cd) is candidate key and R(ABCDEF) #DOUBT When we use veen digram why we are taking only intersections part only ??? Need help please explain ..
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In basic time stamp ordering W-time stamp (Q) denotes the largest time stamp of any transaction that has executed write-(Q) successfully.Suppose that we define W-time stamp(Q) as the most recent transaction to execute Write(Q) successfully.Which is true? 1)both ... both with give same result in few cases 3)both with give different result in all cases 4)both with give different result insome cases
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Some where I have read, that WR, RW, WW problem occurs only in un-serializable schedule, and Irrecoverable problem, cascade less rollback problem and lost update problems occur in serializable schedule. Is the above statement true or false?
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Consider a Serial Schedule given- T1 T2 T3 w1(A) w1(B) r2(A) w2(B) r3(A) w3(B) How many schedules which are view equivalent to above schedule? How many schedules which are confilct equivalent to above schedule? Is this schedule conflict serializable/ view serializable? If yes How many serial schedules are possible which are conflict equivalent/ view equivalent to able schedule?
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14
How to order these schedules in terms of flexibility of concurrency? 1. View serializable 2. Conflict Serializable 3.Recoverable 4.Strict 5.Cascadeless
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T1: r1(x)w1(x)r1(y)w1(y) T2: r2(y)w2(y) L is xclusive lock and U is unlock L1(y)L1(X)R1(Y)W1(Y)R1(X)W1(X)U1(X)U1(Y)L2(Y)R2(Y)W2(Y)U2(Y)? IS THIS SCHEDULE VALID UNDER A 2 PHASE LOCKING SCHEDULER????
1 vote
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I have been reading about the tree protocol as an approach in locking management in databases. I read that it is deadlock free but I am not sure how it works. Example: Assume that T1 has locked B, D, E in exclusive mode. According to the rules: T2 can lock H (allowed by ... lock G it has to lock D but D is locked by T1 so it has to wait. Hence deadlock. What am I misunderstanding in the algorithm?
18
Does the conservative two phase locking protocol produce cascadeless schedules? Let us consider the following schedule : Since in the schedule the lock on a is released, it is possible for the transaction T2 to acquire the lock on a. Now the transaction T2 ... purposes. Does it mean that even though a conservative two phase protocol is used, the schedules may not necesssarily be cascadeless?
19
How to check if a schedule is allowed in 2PL or not? S1:R2(A)W1(B)W1(C)R3(B)R2(B)R1(A)R2(C)W3(A) S2:W2(A)W1(A)W3(A)W2(B)W1(B)W3(B)
1 vote