# FAQs

## when do I need to provide subquery url for `eth-rpc-adpater` or `EvmRpcProvider`?

**short answer**

you need it when you ...

* need to query for historical logs or tx receipts that exist **before** you start the provider or rpc adapter
* OR need to query for logs or tx receipts that's older than [MAX\_CACHE\_SIZE](https://evmdocs.acala.network/miscellaneous/broken-reference), which defaults to 200.

**explanation**

Transactions and logs from unfinalized blocks only live in cache, so new transactions will usually be in the cache first (for a couple blocks), then live in both the cache and the subquery, later, after the cache expires, they only live in subquery.

Developers who run a mandala node and eth-rpc-adaptor locally, usually won’t need to start any subquery or database services for testing, since new transaction receipts and logs will be in cache and findable without subquery.

For simple local testing setup, we can set a large `MAX_CACHE_SIZE` for rpc adapter, such as 10000 blocks. So even without subquery, we should be able to query for receipts and logs for as many as 10000 blocks.

![Cache vs. SubQuery representation](https://399453287-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FAr4HPdeSWiuUx1XzEALT%2Fuploads%2FPlyMzDbTHGJyxKgFrUTR%2Fwiki.png?alt=media\&token=6eddbd2b-461f-4509-abff-5b76bdd412e3)

## why tx failed after I manually changed gas params in metamask?

Acala EVM+ uses encoded `gasPrice` and `gasLimit`, so manually inputting random gas parameters might fail to decode. Please refer to [gas parameter](https://evmdocs.acala.network/network/gas-parameters) section for detailed explanations.

## why metamask tx doesn't confirm with local mandala?

Metamask will sometimes cache the nonce locally, which is used to infer next tx nonce. For example, if we send a tx with nonce 3, metamask will set nonce 4 for next tx. However, after we restart the local mandala node, all accounts are reset and the nonce is back to 0, but metamaks doesn't know it!

As a result, the account with nonce 0 send a tx with nonce 4, which won't be mined and got stuck!

To solve this, we need to reset metamask after restarting local Mandala, so the nonce and cache will be cleared: `settings => advanced => reset account`. Or we can simply manually override the nonce to `0` for the first metamask tx after restarting the network.

## I have balance in metamask, but transfer failed

Metamask shows **total balance**, which might include non-transferable balances. For example, if some of your ACA is staking, they will still show in metamask, but can't be transfered.

We can check the transferable balance in the `Accounts` section in [polkadot.js app](https://evmdocs.acala.network/tooling/chain-explorer#polkadotjs-app)

## tx failing reason not showing in blockscout

Every EVM+ transaction is essentially a substrate transaction, so we can find more details about it in [substrate chain explorer](https://evmdocs.acala.network/tooling/chain-explorer#substrate-chain-explorer).

For example, for [this failing tx](https://blockscout.acala.network/tx/0xec304c62a61c56680522c09a80c7280fe4d985038203df70435cc925a7fe877f/internal-transactions), we can copy and paste the tx hash into the [Acala Subscan](https://acala.subscan.io/), which takes us to the [tx details page](https://acala.subscan.io/extrinsic/0xec304c62a61c56680522c09a80c7280fe4d985038203df70435cc925a7fe877f), the exact error should show up in the bottom `Events` section.

In this case `ReserveStorageFailed` means account balance not enough.

![tx failed reason](https://399453287-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FAr4HPdeSWiuUx1XzEALT%2Fuploads%2Fgit-blob-b1daa615f57801fbc8caa4a5f14682b1abc1bfff%2Fsubscan.png?alt=media)

## how to check if a transaction is finalized?

there are 2 ways:

* use `eth_getBlockByNumber` with `finalized` block tag to get the latest finalized block number, and compare the tx block number with it.
* use EVM+ specific RPC calls: [eth\_isTransactionFinalized](https://evmdocs.acala.network/miscellaneous/broken-reference) or [eth\_isBlockFinalized](https://evmdocs.acala.network/miscellaneous/broken-reference).