Question Assignment description
One says that historical past H is recoverable if, each time transaction Ti reads (some merchandise x) from transaction Tj (i 6= j) in H and Ci happens in H, then Cj ≺S Ci . Ti “reads x from” Tj in H if 1. Wj(x) ≺H Ri(x), and a pair of. Ajnot ≺H Ri(x), and three. if there’s some Wk(x) such that Wj(x) ≺H Wk(x) ≺H Ri(x), then Ak ≺H Ri(x). Which of the following histories are recoverable?H1 =W2(x),W1(x),R3(x),R1(x),C1,W2(y),R3(y),R3(z),C3,R2(x),C2H2 =H3 =H4 =