Uniswap – How to Handle High Gas Flashbots Transactions

The gas limit should be as high as your transaction will consume, and no higher. The amount of gas a transaction consumes depends on what it does. (Bear in mind that if your transaction results in gas refunds, for example because it deletes storage data, you still need to account for it in the gas you supply.)

Most miners will fill blocks up to the limit, and it's OK to set a limit that takes close to or all the gas available in a block, but since miners take transactions with higher fees first, this will increase the gas level you will need to set to outbid other transactions that could fit in the block. So you will need to compensate for the higher gas limit by setting a higher gas price. See https://ethgasstation.info/ for specific data on how high a gas price you are likely to need for any given gas limit.

If you're just doing a simple send, just use 21,000.

The official flashbots searcher onboarding guide is a good source to get started.

• block.coinbase in Solidity refers to the miner of the current block. You can use the ethers.js flashbots bundle provider to bundle your transactions with a final call to the Flashbots "CheckAndSend" contract. That way, the miner will only be rewarded, if the previous transactions of your bundle were successful. (The miner will not include your bundle, if he doesn't get rewarded.)

• The flashbots bribe is independent from the current gas price. You're competing with the bribes of other flashbot searchers. Currently MEV geth only allows for the inclusion of one flashbots bundle per block (but this may change soon). Generally speaking, the less alpha, the higher the bribe. Meaning, if you intend to be running widespread simple arbitrage code, consider bribing with 99% of the arbitrage profit, to get your bundles mined at all (hopefully).

• Unless you have private connections to miners with significant hash rate, you'll probably want to use (and trust) the official flashbots relay, which is also used in the ethers.js flashbots bundle provider. Check this example from its readme:

// Using the map below ships two different bundles, targeting the next two blocks
const blockNumber = await provider.getBlockNumber()
const minTimestamp = (await provider.getBlock(blockNumber)).timestamp
const maxTimestamp = minTimestamp + 120
const bundlePromises = [blockNumber + 1, blockNumber + 2].map((targetBlockNumber) =>
  flashbotsProvider.sendBundle(
    [
      {
        signedTransaction: SIGNED_ORACLE_UPDATE_FROM_PENDING_POOL // serialized signed transaction hex
      },
      {
        signer: wallet, // ethers signer
        transaction: transaction // ethers populated transaction object
      }
    ],
    targetBlockNumber, // block number at which this bundle is valid
    {
      minTimestamp, // optional minimum timestamp at which this bundle is valid (inclusive)
      maxTimestamp, // optional maximum timestamp at which this bundle is valid (inclusive)
      revertingTxHashes: [tx1, tx2] // optional list of transaction hashes allowed to revert. Without specifying here, any revert invalidates the entire bundle.
    }
  )
)