Courses/Distributed Systems

Distributed Systems

CS3.401

Prof. Kishore Kothapalli•Monsoon 2025-26•4 credits

Revision Notes/Unit 5 — Distributed Mutual Exclusion

Unit 5 — Distributed Mutual Exclusion

Five canonical distributed mutex algorithms: Lamport (3(N-1) msgs, FIFO), Ricart-Agrawala (2(N-1) msgs, no FIFO), Maekawa (3√N → 5√N quorum-based with V2 deadlock fix), Suzuki-Kasami (token broadcast, 0 or N msgs), Raymond (token tree, O(log N) msgs). Safety / liveness / fairness; message complexity, synchronisation delay, throughput.

Lamport, Ricart-Agrawala, Maekawa, Suzuki-Kasami, Raymond — Complete Comparison

22 min

Mutual exclusion in a distributed system is the same idea as a critical section in OS — except there's no shared memory, no semaphore, no central arbitrator. Everything is messages. Five algorithms attack the problem in two families: **non-token** (request-permission from peers — Lamport, R-A, Maekawa) and **token** (a single token grants entry — Suzuki-Kasami, Raymond). Trade-offs: message count, synchronisation delay, FIFO requirement, fault behaviour.