Distributed Consensus Algorithms
Achieving Agreement in Distributed Systems Understanding Distributed Consensus
Raft and Paxos both solve consensus but differ in approach. Raft: desi
handles all requests), separates leader election from log replication, easier to implement correctly. Paxos: more general, allows
multiple proposers, theoretically elegant but complex, harder to understand and implement. Raft benefits: easier to teach,
available). Example: 5 nodes, need 3 for quorum, tolerate 2 failures.
overlap), (2) Liveness (progress if quorum available). Distributed systems use quorums for: reads (read from quorum), writes (write
to quorum), elections (need quorum votes). Quorum size is fundamental to consensus—trade-off between fault tolerance and availability.
Frequently asked questions
What is consistency in the context of distributed systems?
Consistency refers to maintaining a single, accurate state across all nodes in a distributed system. It’s simpler than full consensus, often achieved with a single leader node that dictates updates.
When does correctness require achieving agreement among multiple nodes?
Correctness in a distributed system is fundamentally tied to the ability of nodes to agree on a common state or value – this is what consensus algorithms like Raft and Paxos address.
Can you describe the phases involved in the Paxos algorithm?
The Paxos algorithm operates through three distinct phases: (1) Prepare, where a proposer sends a prepare message with a proposal number to acceptors; (2) Accept, where the proposer then sends an accept message with a value if no higher prepare message was received; and (3) Learn, where learners discover the agreed-upon value.
What is quorum in distributed systems and why is it important?
A quorum represents the minimum number of nodes required to make a decision or reach an agreement. This ensures fault tolerance – if more than half of the nodes are available, the system can continue operating even with failures.
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