Designing Data-Intensive Applications by Kleppmann Martin

Author:Kleppmann, Martin
Language: eng
Format: epub
Publisher: O'Reilly Media Inc.
Published: 2017-03-17T04:00:00+00:00

Multi-leader replication (not linearizable)

Systems with multi-leader replication are generally not linearizable, because they concurrently process writes on multiple nodes and asynchronously replicate them to other nodes. For this reason, they can produce conflicting writes that require resolution (see “Handling Write Conflicts”). Such conflicts are an artifact of the lack of a single copy of the data.

Leaderless replication (probably not linearizable)

For systems with leaderless replication (Dynamo-style; see “Leaderless Replication”), people sometimes claim that you can obtain “strong consistency” by requiring quorum reads and writes (w + r > n). Depending on the exact configuration of the quorums, and depending on how you define strong consistency, this is not quite true.

“Last write wins” conflict resolution methods based on time-of-day clocks (e.g., in Cassandra; see “Relying on Synchronized Clocks”) are almost certainly nonlinearizable, because clock timestamps cannot be guaranteed to be consistent with actual event ordering due to clock skew. Sloppy quorums (“Sloppy Quorums and Hinted Handoff”) also ruin any chance of linearizability. Even with strict quorums, nonlinearizable behavior is possible, as demonstrated in the next section.

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