System Behavior Models

Mental models for understanding how systems act under load and failure.

Model	One-Liner
Little's Law	L = lambda W -- concurrency equals arrival rate times latency
Amdahl's Law	Speedup is bounded by the serial fraction
CAP Theorem	Consistency, Availability, Partition Tolerance -- pick two
PACELC	Extends CAP: during partitions choose A/C, else choose L/C
Queueing Theory	Queue length explodes as utilization approaches 100%
Swiss Cheese Model	Failures need aligned holes through multiple defense layers
Blast Radius	How far does a single failure propagate?
Failure Domains	What fails together should fail together -- and nothing else
Graceful Degradation	Shed load to preserve core function

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• Mental Model Library
• Mental Model: Amdahl's Law
• Mental Model: Blast Radius
• Mental Model: CAP Theorem
• Mental Model: Failure Domains
• Mental Model: Graceful Degradation
• Mental Model: Little's Law
• Mental Model: PACELC
• Mental Model: Queueing Theory
• Mental Model: Swiss Cheese Model