How can we get a snapshot of all balances at a certain block?

Question

Which api/rpc call and method do I need to use to extract the state of all balances at a certain block?

Let's use Polkadot and recent block as an example: https://polkadot.js.org/apps/?rpc=wss%3A%2F%2Fpolkadot.api.onfinality.io%2Fpublic-ws#/rpc

Answer 1

First, set up a Polkadot JS API connection for the block you want:

const provider = new WsProvider(endpoint);
const api = await ApiPromise.create({ provider });
const blockHash = await api.rpc.chain.getBlockHash(blockNumber);
const api_at = await api.at(blockHash);

Then, you can easily get a list of all the account entries. I recommend using entriesPaged, else the query may be too overwhelming for the RPC endpoint:

let lastKey = "";
let pageSize = 100;
let all_accounts = await api_at.query.system.account.entriesPaged(
    {
        args: [],
        pageSize: pageSize,
        startKey: lastKey,
    }
);

Then you can query those accounts for their balance information:

for (account of all_accounts) {
    // `account` will be an array of two items: key and value.
    // We know that the last 32 bytes of the storage key is the address of the account.
    let address = encodeAddress(account[0].slice(-32));

    // We can then extract the user's balance information.
    let free = account[1].data.free;
    let reserved = account[1].data.reserved;

    // Update the last key.
    lastKey = account[0].toString();
}

Then repeat this process until you have queried all the accounts.

You can find an example of this here: https://github.com/shawntabrizi/substrate-balance-snapshot

Answer 2

If you want to use the Subscan API you may query their accounts list request url to extract the state of all balances at the latest block.

I created this script to query all the accounts at the latest block using the Subscan API and store them in a file. If you wanted all the Polkadot accounts on its latest block you would get a Subscan API Key, switch to a recent version of Node.js, and run the following, and then wait for it to fetch all the data and store it in a file that is generated in the data/ subfolder:

git clone https://github.com/DataHighway-DHX/open-polkadot-js-library
cd subscan
yarn
SUBSCAN_API_KEY=<INSERT_SUBSCAN_API_KEY> ENDPOINT=polkadot.api.subscan.io node index.js