Glossary term
What is Quorum? Meaning for developers
In System Design
A majority (or W + R > N) must agree. Example: 3 replicas: write to 2, read from 2 → always see the latest.
Learn it properly · System DesignLesson 24: Database Replication: Leader, Follower and BeyondOne database server will eventually die, drown in reads, or be too far from your users. How leader-follower replication works, what replication lag does to real users, why failover is so hard, and how multi-leader and quorum systems handle conflicts.In System Design Case Studies 2
Read from R and write to W of N replicas with R + W > N, so every read overlaps the latest write.
Learn it properly · System Design Case Studies 2Lesson 1: Design a Key-Value Store (Like Redis or Dynamo)A write-ahead log and snapshots on one node, then a consistent-hash ring, N/R/W quorum and version vectors across many.