Introduction to Benchmarking

This section will touch briefly on the concept weights and benchmarking in Substrate. While this section will not go in-depth, any Substrate developer should know it when developing a pallet. In the long run, producing production-ready pallets will become crucial.

Weights in Substrate

Until now, fees have not been a concern for our Connect pallet because we are in dev_mode. However, fees are a reality within the realm of pallet development.

Weight in Substrate refers to the overall computational, storage, and execution cost of a particular extrinsic (state change). Weight is the measurement of the amount of time that a state change takes to execute fully. One unit of weight is equal to one picosecond of execution time on reference hardware.

Based on this weight, a fee is charged to the sender of the extrinsic.

An Introduction to Benchmarking

To calculate an appropriate weight for an extrinsic, Substrate's benchmarking suite can test each extrinsic load to estimate how much weight each state change would take. A weights.rs file is generated via the included CLI and exposes a set of pre-defined weights to use as part of the dispatchable function declaration.

Like unit testing, each extrinsic should have a corresponding benchmarking function within benchmarking.rs.

note

As a general note, we are using Benchmarking V2 within this course, which uses procedural macros to declare benchmarking tests.

Example: Baseline Benchmark for register

The following test is a simple benchmark that uses several features. Usually, the idea is to benchmark each logical execution path for your extrinsic. When calling the extrinsic, we utilize the #[extrinsic_call] macro within our benchmarking function.

Because our function is quite simple, we only have a single baseline benchmark for our function, register:

#[benchmark]
fn register_an_account() {
    let caller: T::AccountId = whitelisted_caller();

    T::Currency::make_free_balance_be(&caller, 10u32.into());

    let very_long_name = b"123456789".to_vec();
    let very_long_bio = b"USOsEy3cAmZudmWyUEMdlU6wVXsZeMj7Ts8rh7Laur3L1ZpvvorGOcZw17mDGtNhmxqYRnANsOxhhfauuRxJhz1PRtHKoXai0i3lT0cTFqpCGODLvRxk8MOiMmVMdoylxwXYMVMwoYuZJQStM9t8k4m9aESUQ5rcCkH408t9s4Yz3WfyvbZfF5bROFgrHug9uk4Iar7Q".to_vec();

    #[extrinsic_call]
    register(RawOrigin::Signed(caller.clone()), very_long_name, very_long_bio);
    assert!(<RegisteredUsers<T>>::get(&caller).is_some());
}