CAP Theorem Explained — Why Every Distributed System Makes This Trade-Off | System Design Basics

Your bank's database loses connectivity between datacenters. Two choices: show every user their last known balance (possibly wrong) — or return an error until the network recovers. That choice is the CAP theorem. And every distributed system makes it — whether engineers thought about it or not. In this video, we build a complete mental model of CAP: why partition tolerance is mandatory, what CP and AP systems actually do during a partition, where ZooKeeper, Cassandra, DynamoDB, and PostgreSQL sit on the triangle, and the PACELC extension that governs steady-state latency vs consistency trade-offs.

✅ What you'll learn:
→ Why Partition Tolerance is mandatory — you cannot opt out in any distributed system
→ The real CAP choice: CP = error during partition · AP = stale data during partition
→ CP in action: ZooKeeper · HBase · etcd — exactly what "return error" looks like on a diagram
→ AP in action: Cassandra · DynamoDB — divergent writes, conflict resolution, eventual consistency
→ 12 real systems positioned on the CAP triangle with justifications
→ PACELC: latency vs consistency in steady state — Cassandra's consistency levels explained
→ 4-question interview framework: finance vs social · merge-ability · per-operation configuration

🕐 Chapters:
0:00 ⚖️ CAP Theorem — The Trade-Off Every Distributed System Must Make
4:22 ⚖️ Three Properties, One Impossible Triangle
6:24 🔌 What a Network Partition Looks Like
8:22 ⚖️ C · A · P — Precise Definitions
11:17 🔒 CP Systems — Consistency Over Availability
13:18 🌐 AP Systems — Availability Over Consistency
17:08 🌐 Real Systems on the CAP Triangle
20:42 ⏱️ PACELC — The Trade-Off That Matters in Steady State
23:01 🎯 The Interview Framework — Choosing CP or AP
25:54 🌏 Why CAP Changed How We Build Systems
28:59 ✅ Done

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📌 Video #7 of the System Design Fundamentals series.
Previous → Consistent Hashing & Sharding [https://www.youtube.com/watch?v=ZMCOhcvlB5c&list=PLqBKiJPu5a1nlrXt6FDE4l5-eIKVGrLY5]
Next → How Load Balancers Work [link once published]

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🔗 Full series playlist → [https://www.youtube.com/watch?v=ZMCOhcvlB5c&list=PLqBKiJPu5a1nlrXt6FDE4l5-eIKVGrLY5]
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#CAPTheorem #SystemDesign #DistributedSystems #ByteLearn #Consistency #Availability #PartitionTolerance #Cassandra #DynamoDB #ZooKeeper #BackendEngineering #systemdesigninterview

Видео CAP Theorem Explained — Why Every Distributed System Makes This Trade-Off | System Design Basics канала ByteLearn