The Logical Tax — Consistency is a Loan You Repay in Round Trips
Every consistency guarantee is a loan taken against latency: you borrow ordering and pay back in round trips. The consistency spectrum from strict serializability to eventual consistency is a price list — every level has a denominated RTT cost. Every consensus protocol sets a coherency coefficient beta that determines where N_max sits. Right-sizing the loan means choosing the minimum guarantee the application requires, implemented with the protocol that delivers it at the lowest beta the team can operate. This post prices each level, compares the protocols, and adds the read-path merge tax that conflict-free merge structures defer from writes to reads.