Writing a scenario

A scenario is an ES module whose default export is a function. It gets the loaded module and drives it the way a page would:

export default async function (engine) {
  const orders = new engine.Engine();
  // load data, run queries, pivot …
  orders.free();
}

peakmark runs the function repeat times in one fresh Node process, then reads the module’s linear memory. A scenario that throws stops the check and its message is shown.

What the function receives

• With glue set, the glue is imported as an ES module. A default export that is a function is called as wasm-bindgen --target web expects, and the scenario gets the resulting module.
• Without glue, the module is instantiated without imports and the scenario gets its exports.

Choosing a realistic flow

Linear memory only grows, so the value that matters is the highest one a flow reaches. Load the amount of data a page would load and run the operations it would run. A scenario that touches nothing proves nothing about memory.

Release what you allocate

growth_per_run is what each run after the first adds, averaged. Free what the scenario creates (free() on wasm-bindgen objects) and a run that returns to its starting point adds nothing. A budget of "0" then fails when a leak appears.

Several scenarios

Each scenario runs in its own Node process. With several scenarios on a module, the module’s value is the highest one, and a finding names the scenario it came from.