loom-performance-testing

# Performance Testing ## Overview Validate that a system meets latency, throughput, and stability targets under load, and locate the bottleneck when it doesn't. This file assumes you can write the test code; it focuses on the measurement traps that make load-test numbers lie and the decision criteria for tool/shape selection. ## Core Concepts (read first — these are where numbers go wrong) ### Open vs. closed workload models The single most consequential choice. It determines what your numbers mean. | Model | Load driver | Throughput is… | Overload behavior | Use for | | ---------- | ------------------------------------ | ------------------------ | ------------------------------------------------ | -------------------------------- | | **Closed** | Fixed VUs, each loops request→wait | *Emergent* (backpressure) | Self-throttles: slow server → fewer requests sent | Modeling a fixed client pool | | **Open** | Fixed *arrival rate* (req/s) | *Controlled* (you set it) | Queue grows unbounded; latency explodes | Web traffic, finding breaking pt | ⚠ **Closed models hide overload.** With fixed VUs, when the server slows down each VU sends *fewer* requests, so offered load silently drops. You can't overwhelm the server past what its own latency allows — you measure a moving target, not capacity. Real internet traffic is open (users arrive independently of serv...