Question 1041

Quorum Arithmetic

A leaderless store replicates every key to N=5 nodes and is configured with W=2 and R=2. A client writes a key, gets success, and a moment later another client reads it and gets the previous value even though no node has failed. Why?

A

The read count must equal the write count for overlap, so R = 2 with N = 5 requires W = 2 to be raised to 5

B

W + R = 4 is not greater than N = 5, so the two nodes read can be entirely disjoint from the two nodes written

C

Reads in a leaderless store always return the value from the node with the lowest latency, ignoring version metadata

D

W = 2 means the write was queued on two nodes but not durably applied until all five nodes acknowledge