Consider the following schedule. Explain what happens when transactions try to execute as per this schedule and the DBMS uses timestamp-based concurrency control. We use ST to denote the start of a transaction, C for commit,
and A for abort.
ST1 → ST2 → ST3 → ST4 → R2(X) → R1(X) → W2(X) → W4(X) → W1(X) →
C1 → W3(X → A4 → R2(Y ) → W2(Y ) → R3(Y ) → C2 → W3(Y ) → C3
(Fill in the table below showing what happens as the transactions execute):
T1 T2 T3 T4 X Y
1 2 3 4 RT = 0 RT = 0
WT = 0 WT = 0
C = true C = true
R2(X)
Consider the following schedule. Explain what happens when transactions try to execute as per this schedule and the DBMS uses multiversion concurrency control:
ST1 → ST2 → ST3 → ST4 → R1(X) → R3(X) → W3(X) → R2(X) → R4(X) →
W2(X) → W4(X)
(Fill in the table below showing what happens as the transactions execute):
T1 T2 T3 T4 X0 . . .
1 2 3 4
R1(X) RT = 1