Question
Databases System. Exercise 18.2.1. Below are two transactions, described in terms of their effect on two database elements A and B, which we may assume
Databases System. Exercise 18.2.1. Below are two transactions, described in terms of their effect on two database elements A and B, which we may assume are integers.
T1: READ(A,t); t:= t+ 2 ; WRITE(A , t ) ; READ(B,t); t:= t* 3 ; WRITE(B,t);
T2: READ(B,s); s:= s*2; WRITE(B,s); READ(A,s); s:=s+3; WRITE(A.s);
We assume that, whatever consistency constraints there are on the database, these transactions preserve them in isolation. Note that A = B is not the consistency constraint.
a) It turns out that both serial orders have the same effect on the database; that is, (T1 ,T2) and (T2,T1) are equivalent.
The question: Demonstrate this fact by showing the effect of the two transactions on an arbitrary initial database state.
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