Experiments

The Bully Election Algorithm The Bully Algorithm, proposed by Hector Garcia-Molina in 1982, is a classic leader election algorithm for distributed systems. It’s called “bully” because the highest-numbered process always wins and “bullies” the others into accepting it as leader. The Scenario A distributed system needs a coordinator: N nodes in a network Each node has a unique ID (priority) One node must be elected as leader When the leader fails, a new leader must be elected Rule: The node with the highest ID wins The protocol: ...

The Fairness Problem We’ve seen two extremes: Readers preference: Writers can starve Writers preference: Readers can starve The fair solution ensures no starvation - everyone gets served in the order they arrive. The Solution: FIFO Ordering Key idea: Use a queue to serve requests in arrival order. This prevents both reader and writer starvation. Arrival Order: R1, R2, W1, R3, R4, W2 Execution: R1+R2 → W1 → R3+R4 → W2 (batch) (excl) (batch) (excl) Consecutive readers can still batch together, but writers don’t get skipped! ...

The Byzantine Generals Problem The Byzantine Generals Problem, proposed by Leslie Lamport, Robert Shostak, and Marshall Pease in 1982, is one of the most important problems in distributed systems. It addresses the challenge of achieving consensus when some participants may be faulty or malicious. The Scenario Byzantine army divisions surround a city: N generals command their divisions They must coordinate: attack or retreat They communicate via messengers Some generals are traitors who send conflicting messages Goal: All loyal generals must agree on the same plan The challenge: ...

The Readers-Writers Problem The Readers-Writers problem is fundamental in concurrent systems where data is shared between multiple threads: Readers: Can access data simultaneously (read-only, no conflicts) Writers: Need exclusive access (modifications can’t overlap) The challenge: Maximize concurrency while maintaining data integrity. Real-World Applications This pattern is everywhere: Databases: SELECT queries (readers) vs UPDATE/INSERT (writers) Caching: Cache reads vs cache updates Configuration: Reading config vs reloading config File systems: Multiple readers, exclusive writes Web servers: Read sessions vs update sessions Readers Preference Solution In this variant, readers get priority: ...

The Drinking Philosophers Problem The Drinking Philosophers Problem is a generalization of the classic Dining Philosophers Problem, proposed by K. M. Chandy and J. Misra in 1984. Unlike the dining version where philosophers share forks with immediate neighbors in a circle, drinking philosophers share bottles with arbitrary neighbors based on a conflict graph. This makes it much more realistic for modeling real-world resource allocation. The Scenario The drinking party has: ...