Foundations

What scalability quantifies beyond raw speed and why designing for growth early avoids costly rewrites

Fix-sized speed versus how latency degrades as load grows 10x, and which you optimize first

p50/p99 latency versus requests per second, Little's Law, queuing and why optimizing one can hurt the other

99.9 vs 99.99 uptime math and what breaks when replicas diverge — the intuition behind CAP