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Optimistic Concurrency Control (cont)

Validation check for transaction T
  • for all transactions Ti  ≠  T
    • if V(Ti) < A(T) < F(Ti), then check W(Ti) ∩ R(T) is empty
    • if V(Ti) < V(T) < F(Ti), then check W(Ti) ∩ W(T) is empty
If this check fails for any Ti, then T is rolled back.

Prevents: T reading dirty data, T overwriting Ti's changes

Problems: rolls back "complete" tx's, cost to maintain A,V,F sets