1125-CMcBride

1125-CMcBride - Defintion: Conflict Serializability- If S1...

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Notes From Tuesday, November 25th Each transaction has its own working area A A Working area: memory for data processing r A Buffer pool: memory controlled by DBMS w Disks A = 1000 B = 1000 T1 T2 A B r(A) 1000 1000 A = A – 50 900 1050 Buffer r(A) 950 1100 temp = A * 0.1 A = A – temp A = 1000 1000 w(A) T1 A = 950 temp = 100 T2 r(B) B = 1000 A = 900 w(A) B = 1050 B = 1000 r(B) B = 1100 B = B + 50 w(B) B = B + temp w(B) Theory of Serializability Serializability: the feature of being equivalent to serial schedules Conflict serializability View serializability – weaker serializability Basic Assumptions 1. Each operation is atomic
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Notes From Tuesday, November 25th 2. A single transaction will not violate consistency 3. Ignore operations other than R and W * Conflicting operations/instructions Ex: Ti and Tj are transactions Ii = R(Q) Ij = R(Q) Do not conflict Ii = R(Q) Ij = W(Q) Conflict Operations Ii = W(Q) Ij = R(Q) Conflict Ii = W(Q) Ij = W(Q) Conflict Ii = R/W(Q) Ij = R/W(P) Do not conflict
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Unformatted text preview: Defintion: Conflict Serializability- If S1 (schedule) can be transformed into a serial schedule, S0, by swapping only non-conflict operations, S1 is conflict serializable. Ex: S1 S2 T1 T2 T1 T2 r(A) r(A) w(A) w(A) r(A) r(B) w(A) w(B) r(B) r(A) w(B) w(A) r(B) r(B) w(B) w(B) Ex: S1 Possible Serial Schedules T3 T4 T3 T4 T3 T4 R(Q) R(Q) W(Q) W(Q) W(Q) R(Q) W(Q) W(Q) W(Q) Notes From Tuesday, November 25th- Test for serializability- Precedence graph of a schedule Ti Tj- If there is a pair of conflicting operations from Ti to Tj and Ti's operation accesses the data before Tj's does, we draw an edge from Ti to Tj Ti Tj Ex] Draw the Precedence Graph T1 T2 T3 T4 T5 r(x) r(y) r(z) r(v) r(w) r(w) r(y) w(y) w(z) r(u) r(y) w(y) r(z) w(z) r(u) w(u) Notes From Tuesday, November 25th Theorem: A schedule is conflict serializable if its T1 T2 precedence graph is acyclic. T5 T3 T4...
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1125-CMcBride - Defintion: Conflict Serializability- If S1...

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