tailieunhanh - Principles of Database Management Systems - Notes 7: Concurrency Control

Principles of Database Management Systems - Notes 7: Concurrency Control products Concurrency Control, Correctness depends on scheduling of transactions, Returning to Sc, Precedence graph P(S), Schedule F (with simple locking). | Principles of Database Management Systems Notes 7: Concurrency Control Based on lecture notes by Hector Garcia-Molina 1 Concurrency Control T1 T2 DB (consistency constraints) Tn How to prevent harmful interference transactions? => scheduling techniques based on - locks - timestamps and validation 2 Example: T1: Read(A) A A+100 Write(A) Read(B) B B+100 Write(B) Constraint: A=B T2: Read(A) A A 2 Write(A) Read(B) B B 2 Write(B) 3 Correctness depends on scheduling of transactions A schedule - Chronological (possibly interleaving) order in which actions of transactions are executed - A correct schedule is equivalent to executing transactions one-at-a-time in some order 4 Schedule A T1 Read(A); A A+100; Write(A); Read(B); B B+100; Write(B); A 25 T2 B 25 125 125 Read(A);A A 2; Write(A); 250 Read(B);B .

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