Refund fees

[robert-zaremba]

Problem Definition

Setting tx fees is pain in the ass from the user perspective:

• He doesn't really know the gas amount he need for a tx. If he will set too high, then he will be charged more than needed
• It's confusing: fee vs gas price & gas-limit (that's more for tooling - we don't have much narrative to improve that flows)
• Tx will fail if user will use fee that it is too small.

Proposal

Now, with 1) Tx prioritizaiton and 2) post ante handlers we can refund fees. Proposed flow
The gas charged should be max(gas_limit / 2, gas_used) * gas_price (same as proposed in evmos/ethermint#1085)

1. change defaults to use gas-price and gas-limit in tx (CLI) instead of total fee.
2. in pre-ante handler, do as today:
   • verify gas-price against validator min-gas-price (in check-tx)
   • charge gas_limit * gas_price (in deliver-tx)
3. in post-ante handler
   • check the gas spent, and send back to the user the unused refund: gas_limit * gas_price - max(gas_limit / 2, gas_used) * gas_price
4. make min-gas-price setting query-able

Let's talk about viability of this solution.

Related: #2150, evmos/ethermint#1085

[yihuang]

There was a proposal in another issue that only refund min(gas_limit - gas_used, gas_limit / 2) * gas_price
Because our block proposal is based on gas limit, otherwise it's vulnerable to DoS by setting a big gas limit.

[robert-zaremba]

good point! To be able to account in block we would need Tendermint update :/

[alexanderbez]

Personally, I do not find fees or the UX confusing at all. It's all quite simple and everything is documented. Yes, we need gas-adjustment, which is annoying I know, but that's just an artifact of how BaseApp is designed. Apart from that, it's all very simple.

The two big UX pain points are:

1. The need for gas-adjustment
2. Min gas prices not being public

So it's not completely fair to say "pain in the ass".

Anyway. I do agree that a refund mechanism is wanted. Also, we already have an issue for this if you searched: #2150

So we should close this one :)

[robert-zaremba]

I think the right UX is following:

• user sets maximum gas (gas-limit) and gas-price
• user will be refunded as much as possible for not used gas (I understand the issue with the block size, hence refunding half is still better than refunding nothing)
• having stats about validators min gas prices (good point @alexanderbez ).

Instead, currently user has to think in terms of total fees (user has no idea what the total fee of a tx is) and might be afraid of setting higher gas limits. I consider this bad UX. Sometimes I need to manually increase gas limit for some transactions in Kepler to make them pass - that is super annoying.

[robert-zaremba]

I've updated the proposal, and suggest to adopt the solution proposed by @yihuang : evmos/ethermint#1085

[yihuang]

I've updated the proposal, and suggest to adopt the solution proposed by @yihuang : evmos/ethermint#1085

It's actually originally proposed by @ValarDragon, #2150

[alexanderbez]

Yeah, we don't need to two issues. We can close this @robert-zaremba :)

[tac0turtle]

Closing in favor of #2150