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Consistency Patterns — Series 3
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Events a and b have Lamport timestamps 5 and 9. With no other information, what can be concluded?
AEvent a necessarily happened before b causally.
BEvents a and b must have been concurrent.
CThe timestamps alone do not prove that a caused b.
DEvent b necessarily happened before a causally.
A state-based grow-only counter has one component per replica. Two received states are [3, 7] and [5, 6]. What merged state avoids double counting replicated increments?
A[8, 13], with value 21.
B[3, 6], with value 9.
C[5, 7], with value 12.
D[5, 6], with value 11.
A convergent counter allows independent decrements at two replicas. A balance of 1 is seen by both, and each subtracts 1. What does convergence alone guarantee?
AAutomatic rejection of the second real-time request.
BA serial order visible before either replica responds.
CA nonnegative balance without any coordination.
DAgreement eventually, possibly on a negative balance.
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