Serializable Histories Because only the complete execution of txns represents a consistent state, we define a history to be serializable (SR) if its committed projection, C(H), is equivalent to some serial …

Definition. The precedence graph has one node for every TXN in the schedule, and one edge for every pair of conflicting ops Theorem. The schedule is conflict-serializable iff the precedence graph has no …

Equivalent schedules: For any database state, the effect (on the set of objects in the database) of executing the first schedule is identical to the effect of executing the second schedule. Serializable …

Concurrency-control schemes tradeoff between the amount of concurrency they allow and the amount of overhead that they incur. Some schemes allow only conflict-serializable schedules to be generated, …

Example • A schedule that is not conflict serializable: T1: R(A), W(A), R(B), W(B) T2: R(A), W(A), R(B), W(B)

To be serializable, the conflicting operations of T and S must be ordered as if either T or S had executed first. We only care about the conflicting operations: everything else will take care of itself.

Strictly serializable (linearizable) services appear to execute transactions (operations) sequentially, in an order consistent with real time. This restricts a transaction’s (operation’s) possible return values and …