Cannot delete account with large state (Aurora Engine)

[frankbraun]

When stress testing the Aurora Engine with the evm-bully on TestNet and a local node I ran into the problem that I cannot delete accounts anymore. For example on TestNet:

$ near delete evm.evm-bully.testnet evm-bully.testnet
Deleting account. Account id: evm.evm-bully.testnet, node: https://rpc.testnet.near.org, helper: https://helper.testnet.near.org, beneficiary: evm-bully.testnet
Receipt: 
	Failure [evm.evm-bully.testnet]: Error: {"index":0,"kind":{"index":0,"kind":{"DeleteAccountWithLargeState":{"account_id":"evm.evm-bully.testnet"}}}}
An error occured
Error: {"index":0,"kind":{"index":0,"kind":{"DeleteAccountWithLargeState":{"account_id":"evm.evm-bully.testnet"}}}}
    at Object.parseResultError (/home/frank/node_modules/near-cli/node_modules/near-api-js/lib/utils/rpc_errors.js:48:29)
    at Account.signAndSendTransaction (/home/frank/node_modules/near-cli/node_modules/near-api-js/lib/account.js:129:36)
    at processTicksAndRejections (node:internal/process/task_queues:94:5)
    at async exports.deleteAccount (/home/frank/node_modules/near-cli/index.js:193:20)
    at async Object.handler (/home/frank/node_modules/near-cli/utils/exit-on-error.js:36:9)
ServerTransactionError: {"index":0,"kind":{"index":0,"kind":{"DeleteAccountWithLargeState":{"account_id":"evm.evm-bully.testnet"}}}}
    at Object.parseResultError (/home/frank/node_modules/near-cli/node_modules/near-api-js/lib/utils/rpc_errors.js:48:29)
    at Account.signAndSendTransaction (/home/frank/node_modules/near-cli/node_modules/near-api-js/lib/account.js:129:36)
    at processTicksAndRejections (node:internal/process/task_queues:94:5)
    at async exports.deleteAccount (/home/frank/node_modules/near-cli/index.js:193:20)
    at async Object.handler (/home/frank/node_modules/near-cli/utils/exit-on-error.js:36:9) {
  type: 'ActionError',
  context: undefined,
  index: 0,
  kind: {
    index: 0,
    kind: {
      DeleteAccountWithLargeState: { account_id: 'evm.evm-bully.testnet' }
    }
  },
  transaction_outcome: {
    proof: [
      {
        hash: '6SQc6pxBKaQjeiAhnf4ZX1o2oTxH9gwYLaj68LqqCiNW',
        direction: 'Right'
      }
    ],
    block_hash: '3kuqKDFuKaLDZtwdnts8g3tzgHHE7mAyXdXbfGZ5dwLN',
    id: 'D89HzFmbqDyUtz9E4KrsgE6t3WjYTqEerAdpPDf14hyZ',
    outcome: {
      logs: [],
      receipt_ids: [ 'Fx56Gz3kALVjbBQZpC69jyrbPygqiVMV1tqyXQKAQRon' ],
      gas_burnt: 255548500000,
      tokens_burnt: '25554850000000000000',
      executor_id: 'evm.evm-bully.testnet',
      status: {
        SuccessReceiptId: 'Fx56Gz3kALVjbBQZpC69jyrbPygqiVMV1tqyXQKAQRon'
      }
    }
  }
}

So the problem is:

{
  "ActionError": {
    "index": 0,
    "kind": {
      "DeleteAccountWithLargeState": {
        "account_id": "evm.evm-bully.testnet"
      }
    }
  }
}

I traced this in nearcore to these places in the code:

nearcore/core/primitives/src/errors.rs

Lines 435 to 436 in a6bf293

	/// Delete account whose state is large is temporarily banned.
	DeleteAccountWithLargeState { account_id: AccountId },

nearcore/core/primitives-core/src/account.rs

Lines 210 to 212 in a6bf293

	/// Max number of bytes an account can have in its state (excluding contract code)
	/// before it is infeasible to delete.
	pub const MAX_ACCOUNT_DELETION_STORAGE_USAGE: u64 = 10_000;

Why is the deletion of accounts with large states "temporarily disabled" and/or "infeasible"?

While this is probably not a problem for the production deployment of the Aurora Engine (I assume we never want to delete the state there) it makes testing a lot harder and leads to a lot of wasted storage on TestNet, if I always have to create a new account for a test run there.

[bowenwang1996]

@frankbraun see the PR description here #4116. This is an inherent limitation that we cannot circumvent at this point in time. If you want to delete some state, it is better to implement it in the contract itself.

[frankbraun]

Thanks @bowenwang1996 for the pointer. I'll leave this issue open for further discussion until we have decided how to circumvent this for the Aurora Engine.

[frankbraun]

OK, it's not a problem on MainNet for Aurora Engine. Locally it's a non-issue as well. Only on TestNet it means that we create accounts that we cannot delete anymore if we deploy an EVM contract for the evm-bully there.

One idea that was brought up was to delete the state from within the EVM, but according to @artob you can only iterate the contract storage keys via the RPC, not from within the contract. And that’s unlikely to change in the near term.

But since this is not a big issue for Aurora for now, I'm closing the issue.

[bowenwang1996]

but according to @artob you can only iterate the contract storage keys via the RPC, not from within the contract

There is no host functions to do that, but if you use collections from near-sdk you should be able to do that from within the contract.