Parallel Processing

Synode uses lanes to run multiple simulated user sessions concurrently within a single thread.

Lanes

Lanes are fixed execution slots in the tick-based simulator. At each tick, every active lane advances any user that is ready to act. When a lane's user finishes all their journeys, the next user from the pool is assigned to that lane.

import { generate } from '@synode/core';

await generate(journey, {
  time: { duration: '7d' },
  simulation: {
    users: 10000,
    lanes: 8, // 8 lanes run concurrently each tick
    tick: '15m',
  },
});

All lanes share the same dataset memory. Each lane has its own isolated user context.

Choosing a Lane Count

Scenario	Suggested lanes
Quick prototyping / small runs	2–4
Standard generation	4–8
Large runs (100k+ users)	8–16

More lanes means more users progress per tick, which increases throughput. The upper limit is practical memory — each lane holds an active user context.

Scatter

The scatter option adds random timing variation so users don't all start on exact tick boundaries. A scatter of 0.15 randomizes each user's start time by up to ±15% of one tick interval.

await generate(journey, {
  time: { duration: '30d' },
  simulation: {
    users: 5000,
    lanes: 4,
    tick: '1h',
    scatter: 0.15, // ±15% per tick — avoids timestamp clustering
  },
});

Time Windows

Specify when the simulation takes place using the time option. See the Simulation guide for all six valid time window combinations.

// Fixed window
await generate(journey, {
  time: { start: new Date('2026-01-01'), duration: '90d' },
  simulation: { users: 50000, lanes: 8, tick: '1h' },
});

// Rolling window (duration only — ends at now)
await generate(journey, {
  time: { duration: '30d' },
  simulation: { users: 10000, lanes: 4, tick: '30m' },
});

Debug Telemetry

Enable debug to collect detailed metrics about the generation run. Saves a JSON report to telemetryPath.

await generate(journey, {
  time: { duration: '7d' },
  simulation: { users: 5000, lanes: 4, tick: '15m' },
  debug: true,
  telemetryPath: './telemetry.json',
});

Default telemetry path: ./telemetry-report.json.

The telemetry report includes:

• Total events generated
• Users started/completed
• Duration and throughput
• Event validation summary (if schemas configured)