[Lightning-dev] Route reliability<->fee trade-off control parameter

Joost Jager joost.jager at gmail.com
Mon Nov 15 15:25:26 UTC 2021


In Lightning pathfinding the two main variables to optimize for are routing
fee and reliability. Routing fee is concrete. It is the sat amount that is
paid when a payment succeeds. Reliability is a property of a route that can
be expressed as a probability. The probability that a route will be
successful.

During pathfinding, route options are compared against each other. So for
example:

Route A: fee 10 sat, success probability 50%
Route B: fee 20 sat, success probability 80%

Which one is the better route? That depends on user preference. A patient
user will probably go for route A in the hope of saving on fees whereas for
a time-sensitive payment route B looks better.

It would be great to offer this trade-off to the user in a simple way.
Preferably a single [0, 1] value that controls the selection process. At 0,
the route is only optimized for fees and probabilities are ignored
completely. At 1, the route is only optimized for reliability and fees are
ignored completely.

But how to choose between the routes A and B for a value somewhere in
between 0 and 1? For example 0.5 - perfect balance between reliability and
fee. But what does that mean exactly?

Anyone got an idea on how to approach this best? I am looking for a simple
formula to decide between routes, preferably with a reasonably sound
probability-theoretical basis (whatever that means).

Joost
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