Transaction confirmation time issue with MetaMask

[alexdupre]

Waiting for transaction receipt (TransactionResponse.wait()) takes longer than expected with MetaMask, especially when interacting with EVM blockchain with dynamic and fast block creation time. Setting a low provider.pollingInterval value doesn't make any difference.

So I decided to debug the issue and found a few interesting things:

• ethers.js performs a polling on eth_getBlockNumber, waiting for a block number change (by default every 4 seconds)
• MetaMask has a request/response cache that is kept valid until the block number changes: https://github.com/MetaMask/eth-block-tracker/blob/c83a963aac367e9820126d7d5a544044741e0b10/src/PollingBlockTracker.ts#L45
• MetaMask polls for block number changes every 20 seconds: https://github.com/MetaMask/eth-block-tracker/blob/c83a963aac367e9820126d7d5a544044741e0b10/src/PollingBlockTracker.ts#L45

This has the effect that whatever polling interval is set in ethers.js, the returned block number will continue to be same because it comes from the MetaMask cache. On average, with default settings, a confirmation will be detected after 12 seconds, and in 24 seconds in the worst case, ruining the UX of any blockchain with sub-second block finality.

Looking at the MetaMask cache I noticed that it doesn't cache the responses from the eth_getTransactionByHash and eth_getTransactionReceipt calls. More interesting, when one of such calls returns and contains a more recent block number, MetaMask detects it and recognizes that the cache is not valid anymore and that the pending transactions have been confirmed, speeding up also the metamask confirmation pop-up.

[alexdupre]

Related issue on MetaMask: MetaMask/metamask-extension#13302

[Benjythebee]

#945 related?

[alexdupre]

I don't see how, that's related to not mined transactions, this is related to metamask interaction.