FastBids & Sorting

Information on FastBids and the Kairos Sorting Algorithm

The Fast Bids

There are two bid variables that must be considered in totality. Note that their behavior is different:

  1. GasPrice

    • No ceiling

    • Not refunded on revert

    • Collected by EVM

  2. FastPrice

    • Cannot exceed GasPrice

    • Refunded (not charged) on revert

    • Collected by FastLane contract

The bid value is the sum of GasPrice + FastPrice.

Searchers looking to be included at the top of the block will send their fastBids to the FastLane MEV relay. An important parameter that must be included during a submission is the fastGasPrice. The fastGasPrice is the price per gas used a searcher is willing to pay the validator to be included at the top of the block. It comes alongside the standard gas price of the transaction, and both values are taken into account to determine the winner of an auction (see Transactions sorting below). Just like the GasPrice, the fastGasPrice is expressed in gwei terms. The winner of an auction will be required to pay both the GasPrice and the fastGasPrice, or their transaction will be reverted by the FastLane auction smart contract.

The payment of GasPrice is handled the same way as any regular transaction - it does not need any special treatment from the Searcher.

Example: A searcher submits a fastBid with a GasPrice of 50 gwei and a fastGasPrice of 30 gwei, their Kairos transaction (submitFastBid) consumes 32,000 gas, and their contract callback (fastLaneCall) consumes 30,000 gas. After winning the auction, the searcher will be required to pay:

  • 50 gwei * 32,000 gas = 0.0016 MATIC for the standard gas consumption attached to the transaction.

  • 30 gwei * 30,000 gas = 0.0009 MATIC to the FastLane auction smart contract as their fastBid.

Reminder that fastLaneCall is a sub-call in submitFastBid.

The standard gas price is applied to submitFastBid (the whole transaction), while the fastGasPrice is applied to fastLaneCall only.

FastBid Sorting

Upon auction completion (100ms before sealing of the block), fastBids will be sorted and delivered to the validator as follow:

  1. The fastBid with the highest totalPrice wins the auction.

  2. All other fastBids with a higher effectiveGasPrice are discarded.

  3. The (non-discarded) fastBid with the following highest totalPrice wins the next spot.

  4. Repeat steps 2 and 3 until all fastBids are either ranked or discarded.

If an auction has already been won, the transaction will revert quickly, which should save gas for any losing Searchers.

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