when do I need to provide subquery url for eth-rpc-adpater or EvmRpcProvider?
you need it when you ...
need to query for logs
OR need to query for historical tx receipt that exist before you start the provider or rpc adapter
OR need to query for tx receipt that's older than MAX_CACHE_SIZE, which defaults to 200.
Transactions 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 receipt will be in cache and findable without subquery, as long as there is no need for querying the transactions older than 200 blocks.
Also, logs are NOT cached (we will probably implement log cache in the future). So if your tests rely on logs, for example if they call eth_getLogs, you will need subquery.
Cache vs. SubQuery representation
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 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
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.