I'm planning to write a pallet to distribute token to many users in substrate blockchain (Ex: 500k-1m users). Should I do a for loop in a user list and transfer token to them? Do you have any example?

  • Is it a one-time job? Or a call that you could call it multiple times? Oct 5, 2022 at 17:41
  • I like one-time job than call it multiple times. Do you know the advantage/disadvantage of each way. Just wonder can we distribute token to 500k-1m users with one-time job? Oct 5, 2022 at 18:17

1 Answer 1


Both are easy to implement. But if it is an extrinsic call, you might need to pay more attention to the bandwidth/weight costs.

One-time job in migration way.

Find your Executive type in the runtime lib.rs and add a TokenDistribution:

pub type Executive = frame_executive::Executive<
+   TokenDistribution,

Define the struct TokenDistribution and implement OnRuntimeUpgrade for it:

use frame_support::traits::OnRuntimeUpgrade;

pub struct TokenDistribution;
impl OnRuntimeUpgrade for TokenDistribution {
    fn on_runtime_upgrade() -> Weight {
        let fund_account = x;
        let distribute_amount = y;

        load_user_list().into_iter().for_each(|user: AccountId| {
            // `Balances` is the pallet name of your `pallet-balances` 
            // instance which defines in the runtime `lib.rs`           
        // Or you could calculate a more precise weight here

In the next runtime upgrade, the distribution will be applied.

I believe this is the cleanest way to do it.

And remember to remove these codes before the next-next runtime upgrade.

  • Can we do 500k-1m transactions in 1 extrinsic call. Is there any limit by BlockWeight or anything else? Oct 6, 2022 at 7:49
  • 1
    I'm not pretty sure about that. But you could split it into multiple calls. It looks like this Vec<Scheduler::schedule(Utility::batch(Vec<transfer>))>. Make sure that your chain has pallet-scheduler and pallet-utility, Oct 6, 2022 at 8:17

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