• Serializability: isolation between transactions—as if transactions run sequentially.
  • Serializability: multi-operation, multi-object, arbitrary total order
• Linearizability: multiple replicas behaving as if there was a single replica/single copy of data. Every operation happens atomically.
  • Consequence: each op returns up-to-date value
  • Applies to distributed systems and shared-memory concurrency (multi-core CPU caches)
  • Linearizability: single-operation, single-object, real-time order
• Raft
  • Leader election
    • Node state is either follower, leader, or candidate
    • On leader heartbeat timeout: turn self into candidate, request votes from others
    • Everyone votes on longest/most complete log, then on first to timeout (everyone has random timeouts)
    • On stalemate, timeout and retry
  • Log replication
    • Replication requires majority quorum
    • Log entry state is either appended or committed, commits via 2pc
• 3PC: avoid disk write by treating nodes as disk