Distributed Systems Labs Progress Summary

Overview

This document tracks the development progress of the distributed systems labs (MIT 6.5840/6.824). The core focus has been on building a fault-tolerant, linearizable Key-Value store on top of a consensus algorithm.

Lab	Module	Status	Difficulty	Notes
Lab 1	MapReduce	✅ Completed	Low	Implemented basic distributed data processing.
Lab 2	KV Server	✅ Completed	Low	Basic client/server architecture for key-value operations.
Lab 3	Raft Consensus	✅ Completed	High	Implemented leader election, log replication, persistence.
Lab 4	Fault-Tolerant KV	✅ Completed	Medium	Linearizable KV store built on Raft.
Lab 5	Sharded KV	✅ Completed	High	Horizontal scaling via sharding.

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Detailed Status Report

Lab 3: Raft Implementation

• Achievements: Successfully handled leader election, log replication, log compaction (snapshots), and persistence. The implementation passes the standard test suite hundreds of times without failure, demonstrating strong resilience to partitions and crash-restarts.

Lab 4: Fault-Tolerant Key/Value Service

• Achievements: Built a fault-tolerant key/value storage service using above Raft library by implementing a replicated-state machine package and a replicated key/value service with using snapshots.
• Test Artifact:
  • Symptom: In TestBasic4B and TestSpeed4B (reliable network), the client occasionally receives ErrMaybe (approx. 1 in 500-1000 runs) only when running with the -race flag. The host laptop(M3 Air) experiences unusually high temperatures.
  • Observation: If the -race flag is removed, the tests pass thousands of times consistently without failure.
  • Root Cause Analysis: The Go race detector's massive overhead, which distorts the test framework's strict timing expectations(making the code run from 2x to 10x slower).

Lab 5: Sharded KV

• Achievements: Completed implementing a highly-available sharded key/value service with many shard groups for scalability, reconfiguration to handle changes in load, and with a fault-tolerant controller.
• Tips of ChangeCfg in 5B and 5C: Once a configuration wins the race and is saved to the KV server, it will be executed(Unstoppable Mandate). Configs Increase Exactly 1 by 1 (No Skipping).