Transactions: precedence graphsWe consider the following schedule:T1W(D)W(C)R(D)T2W(A)W(C)R(B)T3W(A)W(B)Determine the precedence graph of this schedule. Write the graph in the following format:T1 -> T3T2 -> T3
Question
Transactions: precedence graphsWe consider the following schedule:T1W(D)W(C)R(D)T2W(A)W(C)R(B)T3W(A)W(B)Determine the precedence graph of this schedule. Write the graph in the following format:T1 -> T3T2 -> T3
Solution
Para determinar el grafo de precedencia del cronograma dado, primero identificamos las dependencias entre las transacciones basadas en las operaciones de lectura y escritura. Aquí está el cronograma:
- T1: W(D) W(C) R(D)
- T2: W(A) W(C) R(B)
- T3: W(A) W(B)
Analizamos las dependencias:
-
Dependencias de T1:
- T1 escribe en D y luego lee D. No hay conflicto aquí.
- T1 escribe en C. T2 también escribe en C, lo que crea una dependencia de T1 a T2 (T1 -> T2) porque T1 debe escribir antes de que T2 pueda escribir en C.
-
Dependencias de T2:
- T2 escribe en A. T3 también escribe en A, lo que crea una dependencia de T2 a T3 (T2 -> T3) porque T2 debe escribir antes de que T3 pueda escribir en A.
- T2 escribe en C. Ya hemos identificado la dependencia de T1 a T2.
- T2 lee B. T3 escribe en B, lo que crea una dependencia de T3 a T2 (T3 -> T2) porque T3 debe escribir antes de que T2 pueda leer B.
-
Dependencias de T3:
- T3 escribe en A. Ya hemos identificado la dependencia de T2 a T3.
- T3 escribe en B. Ya hemos identificado la dependencia de T3 a T2.
Con estas dependencias, el grafo de precedencia es:
T1 -> T2
T2 -> T3
T3 -> T2
Sin embargo, la dependencia cíclica T2 -> T3 y T3 -> T2 indica un posible conflicto de serialización.
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