Faker Sims

vantage-faker fills memory tables with generated rows. With its sim feature it also runs Rhai scripts as simulations over the same memory store: each sim is a script with its own clock, and a SimDef spawns copies of it (a burst at start, then a rate per sim minute, up to a maximum alive). Sims write through the data vocabulary from this part of the book, so a Dio, a grid or an API watching the store sees the rows arrive, change and leave.

• A sim script
• Sim words
• The store underneath

A sim script

A faker sim is a Rhai script that runs from top to bottom on its own thread, with its own sim clock. Its local variables are its state, and sleep pauses it. The data vocabulary is there in full, over the engine’s memory store, and table() with no name is the sim’s own table:

if table().where("status", "Placed").count() >= 40 {
    done();
}

let id = table().insert(#{ customer: fake("name"), total: rand_float(5.0, 80.0), status: "Placed" });
sleep(minutes(rand_int(5, 20)));

table().patch(id, #{ status: "Shipped" });
table("order_event").insert(#{ order: id, note: "shipped" });
sleep(hours(2));

table().delete(id);

Sim words

On top of the data vocabulary, sims get:

• data: fake_row() on a handle (table().fake_row(), table("t").fake_row()) returns a map with a generated value for each column the table declares through SimEngineBuilder::columns, without the id column. Sequential generators (walk, evenly spread date) advance one step per call, shared by every sim of the def.
• time: seconds(n), minutes(n), hours(n), days(n), sleep(d), wait_until(t), now(), now_secs(), wall_now(), wall_in(d), elapsed(), clock(), done().
• random: pick, pick_weighted, rand_int, rand_float, chance(p), pattern("BA####"), sentence(min, max), fake(kind), date_between(from, to).
• spawn: spawn_sim(name, args?), sim_id(), sim_name(), and the spawner’s args.
• geo: great_circle, bearing, interpolate.

The store underneath

A sim’s tables are memory Vistas, so reads and writes finish on the first poll and sims run without tokio (see the bridge). Writes broadcast the store’s change events to any watching Dio. During a warm start, each written table stays quiet and sends one Reset at the end. A missing table is a script error: the store’s tables are created by the dataset, not by the sim.

The vantage-faker README covers defs, spawners, clocks, the operations budget and the built-in sims.