don't refund all the unused gas

[yihuang]

Proposal: don't refund all the unused gas

Adapt the cosmos-sdk proposal to ethermint.
Instead of charge user gas_used * gas_price as fee, charge max(gas_limit / 2, gas_used) * gas_price.

Positives:

• Incentivize user to set tx gas limit more responsibly, which will help the block fill rate according to current check tx logic.
  • This motivation will be invalidated after we support abci++, which could happen in next year I guess.
• Disincentivize arbitrage bots which often set a high gas limit to cover the slow path, while most of time enjoy the low gas fee of the fast path.

Negatives:

• Clients need to change how it calculates the tx fee, since it's not compatible with ethereum anymore, we can't expect all the clients will change accordingly.
  • One mitigation of above issue is, return max(gas_limit / 2, gas_used) in place of gas_used in json-rpc, so client still calculate the correct fee, but get a wrong gas_used(we can add a new realGasUsed field?)

Current behavior: refund all unused gas

Desired behavior: only refund a portion of unused gas

Use case:

• better block fill rate
• punish bots

[adu-crypto]

how about we use returned value of eth_estimateGas as estimated gas_used instead of gas_limit when including the txs in block and check only gas_limit when DeliverTx

[yihuang]

that'll make the check tx much heavier, which breaks the assumption of the design, and introduce new dos attack venerability.

[zmanian]

This suggestion has a negative impact on some common patterns in EVM development.

The way Uniswap handle's tx expiration is to have a quick check to see if the block height is greater than zero before doing a swap. This is done while spending much less gas than a swap.

At low transaction fees, these semantic differences won't have a huge impact.

Unfortunately a more holistic solution seems to depend on using ABCI++ to have the proposer actually pre-execute all the transactions

[yihuang]

The way Uniswap handle's tx expiration is to have a quick check to see if the block height is greater than zero before doing a swap. This is done while spending much less gas than a swap.

is this a feature or bug though, this opens the room for bots to do lots of low gas trials, only need to pay the heavier gas when it succeeds.