Long-tail Latency: Causes and Solutions

Issue #105: System Design Interview Roadmap • Section 4: Scalability

What We'll Learn Today

• Latency Distribution Simulator: Real-time system showing P50, P95, P99 metrics

• Cause Injection Engine: Toggle various long-tail latency sources

• Mitigation Strategy Demonstrator: Live comparison of hedging, circuit breakers, and load shedding

• Enterprise Pattern Library: Production-ready patterns from Netflix, Google, and Amazon

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The Silent Performance Killer

Your API reports a blazing-fast 50ms median response time, yet users complain about slow experiences. Welcome to the world of long-tail latency—where the statistical outliers at P95, P99, and P99.9 percentiles can destroy user experience despite excellent averages.

📊 [Long-tail Latency Distribution Curve]

The cruel mathematics: if your P99 latency is 2 seconds, then 1% of users wait that long. At 1 million requests per hour, that's 10,000 frustrated users. Unlike median latency that affects everyone equally, tail latency creates a two-tier user experience.