Explain Raft vs Paxos vs Zab
Raft vs Paxos vs Zab compares three distributed consensus algorithms used to keep multiple servers in sync despite failures.
When to Use
- Paxos: Best for mission-critical systems needing mathematical rigor (e.g., Google Spanner).
- Raft: Ideal for new projects prioritizing simplicity and developer readability (e.g., etcd, Consul).
- Zab: Purpose-built for ZooKeeper clusters to ensure ordered broadcast and leader election.
Example
Think of three friends trying to agree on a movie. Paxos is like a complex voting system, Raft elects one leader to decide, while Zab is a custom rulebook written just for their group.
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Why Is It Important
Consensus ensures data consistency and fault tolerance. Without it, distributed databases, queues, and coordination services would risk split-brain or data loss.
Interview Tips
Start by defining consensus, then contrast: Paxos (proven but complex), Raft (leader-driven and easier to explain), Zab (specialized for ZooKeeper). Drop real-world systems using each.
Trade-offs
- Paxos: Strong correctness, hard to implement.
- Raft: Simpler but less general.
- Zab: Efficient in ZooKeeper but not widely applicable.
Pitfalls
- Over-focusing on protocol phases instead of practical use.
- Confusing Zab with Paxos (Zab is separate).
- Assuming one is always superior—context matters.
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