Consider the following schedules involving two transactions. S 1: r 1(X) ; r 1(Y) ; r 2(X) ; r 2(Y) ; w 2(Y) ; w 1(X) S2 : r 1(X) ; r 2(X) ; r 2(Y) ; w 2(Y) ; r 1(Y) ; w 1(X)
S 1is not conflict serializable and S 2is conflict serializable
In S1, r1(Y) precedes w2(Y), giving T1 → T2, while r2(X) precedes w1(X), giving T2 → T1. The precedence graph has a cycle, so S1 is not conflict serializable. In S2, both conflicts point from T2 to T1: r2(X) precedes w1(X), and w2(Y) precedes r1(Y). Its graph is acyclic, so S2 is conflict serializable in the order T2, T1.
Important Questions from Serializability of Schedules - Teaching
Suppose a database schedule 5 involves transactions T 1, T 2, .............T nConsider the precedence graph of S with vertices representing the transactions and edges representing the conflicts. If S is serializable, which one of the following orderings of the vertices of the precedence graph is guaranteed to yield a serial schedule ?
Consider the following statements:
Statement I: Conservative 2 PL is a deadlock-free protocol.
Statement II: Thomas's write rule enforces conflict serializability.
Statement III: Timestamp ordering protocol ensures serializability based on the order of transaction timestamps.
Which of the following is correct?
Consider the following schedule S.
T1 T2 T3 T4 Timestamp R(X) R(Y) t1 W(X) W(Y) t2 R(Y) R(X) t3 W(Y) W(X) t4 R(X) t5 W(X) t6 R(X) denotes read operation on data item X by transaction Ti.
W(X) denotes write operation on data item X by transaction Ti.
Choose the correct execution order for the above schedule S.
Consider the transactions T1, T2, T3 and the schedules S1 and S2 given below.
T1 : r1(x); r1(z); w1(z)
T2 : r2(y); r2(z); w2(z)
T3 : r3(y); r3(x); w3(y)
S1 : r1(x); r3(y); r3(x); r2(y); r2(z); w3(y); w3(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 ?
Consider following schedules involving two transactions :
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)
Which of the following statement is true ?
