Paxos Consensus Algorithm Quiz and Flashcards

What is the main problem that can occur in the context of liveness in consensus protocol?

What is the Impossibility result mentioned in the text and how is it related to consensus?

What is the scenario described in the example involving simultaneous proposers, prepare, and accept requests?

What happens in the scenario where multiple promises and prepares are made but no progress towards accepting occurs?

How is eventual liveness demonstrated in the context of the scenarios described?

Paxos Consensus Algorithm

Provides safety (only a proposed value can be chosen, and only one value can be chosen) and eventual liveness (consensus is eventually reached, but not guaranteed)

FLP Impossibility Result

Proves that it's impossible to guarantee consensus in an asynchronous system where even one host might fail
In an asynchronous system, there's no upper bound on processing time, clock drift rate, or networking delay
It's impossible to detect reliably whether a host has failed or is just slow

Paxos Algorithm Phases

Phase 1: Leader election
Phase 2: Leader proposes a value and receives acknowledgments
Phase 3: Leader multicasts final value

Paxos Roles

Proposer: receives client requests and tries to get a quorum of acceptors to agree
Acceptor: participant in maintaining distributed storage, agrees on values with a quorum
Learner: learns the agreed-upon value and can be queried later

Synchronous vs. Asynchronous Systems

Synchronous systems have simultaneous steps, can detect faults, and are resilient to faults
Asynchronous systems have no upper bounds on processing time, clock drift rate, or networking delay

Explore the safety and eventual liveness guarantees provided by the Paxos consensus protocol. Learn about the key principles such as only chosen values, single value selection, and eventual consensus. Understand the implications of the FLP result on Paxos' ability to reach consensus.