A key is stored on N = 3 replicas, and writes wait for W = 2 of them. How many replicas must a read ask (R) to be sure it sees the latest write?

Options

• ✗ 1
• ✓ 2 Correct
• ✗ 3
• ✗ It cannot be guaranteed with replicas

Why

When R + W > N, every read set overlaps every write set in at least one replica. 2 + 2 > 3, so R = 2 suffices, and it survives one replica being down.

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