ZmnSCPxj [ARCHIVE] on Nostr: 📅 Original date posted:2021-08-15 📝 Original message: Good morning aj, et al. > ...

📅 Original date posted:2021-08-15
📝 Original message:
Good morning aj, et al.

> Hey *,
>
> There's been discussions on twitter and elsewhere advocating for
> setting the BOLT#7 fee_base_msat value [0] to zero. I'm just writing
> this to summarise my understanding in a place that's able to easily be
> referenced later.
>
> Setting the base fee to zero has a couple of benefits:
>
> - it means you only have one value to optimise when trying to collect
> the most fees, and one-dimensional optimisation problems are
> obviously easier to write code for than two-dimensional optimisation
> problems

Indeed, this is a good point regarding this.


> - when finding a route, if all the fees on all the channels are
> proportional only, you'll never have to worry about paying more fees
> just as a result of splitting a payment; that makes routing easier
> (see [1])

If we neglect roundoff errors.

On the other hand, roundoff errors involved are <1msat per split, so it probably will not matter to most people.

> So what's the cost? The cost is that there's no longer a fixed minimum
> fee -- so if you try sending a 1sat payment you'll pay 0.1% of the fee
> to send a 1000sat payment, and there may be fixed costs that you have
> in routing payments that you'd like to be compensated for (eg, the
> computational work to update channel state, the bandwith to forward the
> tx, or the opportunity cost for not being able to accept another htlc if
> you've hit your max htlcs per channel limit).
>
> But there's no need to explicitly separate those costs the way we do
> now; instead of charging 1sat base fee and 0.02% proportional fee,
> you can instead just set the 0.02% proportional fee and have a minimum
> payment size of 5000 sats (htlc_minimum_msat=5e6, ~$2), since 0.02%
> of that is 1sat. Nobody will be asking you to route without offering a
> fee of at least 1sat, but all the optimisation steps are easier.

Should this minimum a node will be willing to forward be part of gossip, and how does this affect routing algorithms?

> You could go a step further, and have the node side accept smaller
> payments despite the htlc minimum setting: eg, accept a 3000 sat payment
> provided it pays the same fee that a 5000 sat payment would have. That is,
> treat the setting as minimum_fee=1sat, rather than minimum_amount=5000sat;
> so the advertised value is just calculated from the real settings,
> and that nodes that want to send very small values despite having to
> pay high rates can just invert the calculation.

I like this idea, as I think it matches more what the incentives are.
But it requires a change in gossip and in routing algorithms, and more importantly it requires routing algorithms to support two different fee schemes (base + proportional vs min + proportional).

On the other hand, this still is a two-dimensional optimization algorithm, with `minimum_fee` and `proportional_fee_millionths` as the two dimensions.
So maybe just have a single proportional-fee mechanism...

>
> I think something like this approach also makes sense when your channel
> becomes overloaded; eg if you have x HTLC slots available, and y channel
> capacity available, setting a minimum payment size of something like
> y/2/x**2 allows you to accept small payments (good for the network)
> when you're channel is not busy, but reserves the last slots for larger
> payments so that you don't end up missing out on profits because you
> ran out of capacity due to low value spam.
>
> Two other aspects related to this:
>
> At present, I think all the fixed costs are also incurred even when
> a htlc fails, so until we have some way of charging failing txs for
> incurring those costs, it seems a bit backwards to penalise successful
> txs who at least pay a proportional fee for the same thing. Until we've
> got a way of handling that, having zero base fee seems at least fair.

Yes, the dreaded mechanism against payment lockup, which as far as I understand has a lot of thought already sunk into it without any widely-accepted solution, sigh.


Regards,
ZmnSCPxj