A distributed system spreads service or state across independent components so one failed server does not take everything down. Replication across locations provides high availability, but replicas may temporarily disagree. section 12.1.1
A practical distributed database commonly uses:
- A leader that orders writes and updates. section 12.1.1
- Other replicas that serve reads and catch up after replication lag. section 12.1.1
- Eventual consistency, accepting temporary differences while replicas converge. section 12.1.1
When replicas disagree
One server reports that Alice owns 5 billion dollars while another returns a different balance or history. That contradictory state is a fork. Faults, network partitions, crashes, or compromised servers can create this problem; Byzantine fault-tolerant consensus aims to prevent it. section 12.1.2
Use the figure as a visual aid for replicated databases, leader-based writes, and distributed reads. section 12.1.1














