Backpressure

Four job queues, each filling on its own slow drift plus the occasional surge. A fixed pool of workers drains queues, one per lane at rest — no spare capacity sitting idle. Drag a worker onto another lane to move it there, but it takes a beat to spin up before it starts draining again. That warm-up is the whole game: thrash workers around reactively and you pay the warm-up tax over and over while queues you just abandoned back up. Watch the telegraph — each queue flashes a warning a couple of seconds before a surge lands — and reposition ahead of it instead.

Timed to a recent deep-dive on Rails 8.1’s Solid Queue and the “run jobs inside the web process” tradeoff: this is that worker-allocation problem, stripped to its shape.

Reuse

The mechanic lives in src/backpressure.js as a framework-free ES module:

• createBackpressureSim(opts) — returns a state object; call update(dt) each frame and assign(workerId, queueIndex) to move a worker.
• opts: queueCount, workerCount, capacity, drainRate, warmupTime, baseRate, rateAmplitude, surgeMultiplier, surgeDuration, warnLead, surgeIntervalMin/Max, duration (0 for an endless run).
• State exposes queues (each with fill, rate, dropped, warning, surge), workers (each with queueIndex, warmup), totalDropped, and status ('playing' | 'finished'). No rendering or input in the module itself — the demo’s canvas drawing and pointer-drag handling are reference code, not part of the reusable piece.

Gotchas

• Each queue’s arrival rate is a sine wave (baseRate ± rateAmplitude) so its rhythm is readable on its own; surges are a random multiplier layered on top, telegraphed via warning starting warnLead seconds before they land. Both signals are in queue.rate/queue.warning — plot or read them, don’t recompute the wave yourself.
• Defaults leave one worker per queue at rest (no slack), tuned so a surge left uncovered usually overflows but a smart cover-then-return policy roughly cuts drops to a fifth of doing nothing. Changing workerCount relative to queueCount changes that balance a lot.
• The demo bundles its own copy of the module (self-contained by contract). If you touch src/, re-copy it into demo/.