From: Matt Corallo Date: Mon, 24 Apr 2023 05:16:51 +0000 (+0000) Subject: Split out success probability calculation to allow for changes X-Git-Tag: v0.0.117-alpha1~3^2~4 X-Git-Url: http://git.bitcoin.ninja/index.cgi?a=commitdiff_plain;h=75438900b271e09a54c6e97ca9339ac0e36c055f;p=rust-lightning Split out success probability calculation to allow for changes Our "what is the success probability of paying over a channel with the given liquidity bounds" calculation is reused in a few places, and is a key assumption across our main score calculation and the historical bucket score calculations. Here we break it out into a function to make it easier to experiment with different success probability calculations. Note that this drops the numerator +1 in the liquidity scorer, which was added to compensate for the divisor + 1 (which exists to avoid divide-by-zero), making the new math slightly less correct but not by any material amount. --- diff --git a/lightning/src/routing/scoring.rs b/lightning/src/routing/scoring.rs index 26d555819..acb29a0d5 100644 --- a/lightning/src/routing/scoring.rs +++ b/lightning/src/routing/scoring.rs @@ -893,7 +893,7 @@ impl>, L: Deref, T: Time> ProbabilisticScorerU /// [`Self::historical_estimated_channel_liquidity_probabilities`] (but not those returned by /// [`Self::estimated_channel_liquidity_range`]). pub fn historical_estimated_payment_success_probability( - &self, scid: u64, target: &NodeId, amount_msat: u64) + &self, scid: u64, target: &NodeId, amount_msat: u64, params: &ProbabilisticScoringFeeParameters) -> Option { let graph = self.network_graph.read_only(); @@ -905,7 +905,8 @@ impl>, L: Deref, T: Time> ProbabilisticScorerU return dir_liq.liquidity_history.calculate_success_probability_times_billion( dir_liq.now, *dir_liq.last_updated, - self.decay_params.historical_no_updates_half_life, amount_msat, capacity_msat + self.decay_params.historical_no_updates_half_life, ¶ms, amount_msat, + capacity_msat ).map(|p| p as f64 / (1024 * 1024 * 1024) as f64); } } @@ -997,6 +998,23 @@ const PRECISION_LOWER_BOUND_DENOMINATOR: u64 = approx::LOWER_BITS_BOUND; const AMOUNT_PENALTY_DIVISOR: u64 = 1 << 20; const BASE_AMOUNT_PENALTY_DIVISOR: u64 = 1 << 30; +/// Given liquidity bounds, calculates the success probability (in the form of a numerator and +/// denominator) of an HTLC. This is a key assumption in our scoring models. +/// +/// Must not return a numerator or denominator greater than 2^31 for arguments less than 2^31. +/// +/// min_zero_implies_no_successes signals that a `min_liquidity_msat` of 0 means we've not +/// (recently) seen an HTLC successfully complete over this channel. +#[inline(always)] +fn success_probability( + amount_msat: u64, min_liquidity_msat: u64, max_liquidity_msat: u64, _capacity_msat: u64, + _params: &ProbabilisticScoringFeeParameters, _min_zero_implies_no_successes: bool, +) -> (u64, u64) { + let numerator = max_liquidity_msat - amount_msat; + let denominator = (max_liquidity_msat - min_liquidity_msat).saturating_add(1); + (numerator, denominator) +} + impl, BRT: Deref, T: Time, U: Deref> DirectedChannelLiquidity< L, BRT, T, U> { /// Returns a liquidity penalty for routing the given HTLC `amount_msat` through the channel in /// this direction. @@ -1017,9 +1035,9 @@ impl, BRT: Deref, score_params.liquidity_penalty_amount_multiplier_msat) .saturating_add(score_params.considered_impossible_penalty_msat) } else { - let numerator = (max_liquidity_msat - amount_msat).saturating_add(1); - let denominator = (max_liquidity_msat - min_liquidity_msat).saturating_add(1); - if amount_msat - min_liquidity_msat < denominator / PRECISION_LOWER_BOUND_DENOMINATOR { + let (numerator, denominator) = success_probability(amount_msat, + min_liquidity_msat, max_liquidity_msat, available_capacity, score_params, false); + if denominator - numerator < denominator / PRECISION_LOWER_BOUND_DENOMINATOR { // If the failure probability is < 1.5625% (as 1 - numerator/denominator < 1/64), // don't bother trying to use the log approximation as it gets too noisy to be // particularly helpful, instead just round down to 0. @@ -1046,7 +1064,8 @@ impl, BRT: Deref, score_params.historical_liquidity_penalty_amount_multiplier_msat != 0 { if let Some(cumulative_success_prob_times_billion) = self.liquidity_history .calculate_success_probability_times_billion(self.now, *self.last_updated, - self.decay_params.historical_no_updates_half_life, amount_msat, self.capacity_msat) + self.decay_params.historical_no_updates_half_life, score_params, amount_msat, + self.capacity_msat) { let historical_negative_log10_times_2048 = approx::negative_log10_times_2048(cumulative_success_prob_times_billion + 1, 1024 * 1024 * 1024); res = res.saturating_add(Self::combined_penalty_msat(amount_msat, @@ -1056,9 +1075,8 @@ impl, BRT: Deref, // If we don't have any valid points (or, once decayed, we have less than a full // point), redo the non-historical calculation with no liquidity bounds tracked and // the historical penalty multipliers. - let available_capacity = self.available_capacity(); - let numerator = available_capacity.saturating_sub(amount_msat).saturating_add(1); - let denominator = available_capacity.saturating_add(1); + let (numerator, denominator) = success_probability(amount_msat, 0, + available_capacity, available_capacity, score_params, true); let negative_log10_times_2048 = approx::negative_log10_times_2048(numerator, denominator); res = res.saturating_add(Self::combined_penalty_msat(amount_msat, negative_log10_times_2048, @@ -1851,8 +1869,9 @@ mod bucketed_history { #[inline] pub(super) fn calculate_success_probability_times_billion( - &self, now: T, last_updated: T, half_life: Duration, amount_msat: u64, capacity_msat: u64) - -> Option { + &self, now: T, last_updated: T, half_life: Duration, + params: &ProbabilisticScoringFeeParameters, amount_msat: u64, capacity_msat: u64 + ) -> Option { // If historical penalties are enabled, we try to calculate a probability of success // given our historical distribution of min- and max-liquidity bounds in a channel. // To do so, we walk the set of historical liquidity bucket (min, max) combinations @@ -1887,14 +1906,13 @@ mod bucketed_history { } let max_bucket_end_pos = BUCKET_START_POS[32 - highest_max_bucket_with_points] - 1; if payment_pos < max_bucket_end_pos { + let (numerator, denominator) = success_probability(payment_pos as u64, 0, + max_bucket_end_pos as u64, POSITION_TICKS as u64 - 1, params, true); let bucket_prob_times_billion = (self.min_liquidity_offset_history.buckets[0] as u64) * total_max_points * 1024 * 1024 * 1024 / total_valid_points_tracked; cumulative_success_prob_times_billion += bucket_prob_times_billion * - ((max_bucket_end_pos - payment_pos) as u64) / - // Add an additional one in the divisor as the payment bucket has been - // rounded down. - (max_bucket_end_pos + 1) as u64; + numerator / denominator; } } @@ -1912,11 +1930,11 @@ mod bucketed_history { } else if payment_pos < min_bucket_start_pos { cumulative_success_prob_times_billion += bucket_prob_times_billion; } else { + let (numerator, denominator) = success_probability(payment_pos as u64, + min_bucket_start_pos as u64, max_bucket_end_pos as u64, + POSITION_TICKS as u64 - 1, params, true); cumulative_success_prob_times_billion += bucket_prob_times_billion * - ((max_bucket_end_pos - payment_pos) as u64) / - // Add an additional one in the divisor as the payment bucket has been - // rounded down. - ((max_bucket_end_pos - min_bucket_start_pos + 1) as u64); + numerator / denominator; } } } @@ -2719,7 +2737,7 @@ mod tests { let usage = ChannelUsage { amount_msat: 256, ..usage }; assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 106); let usage = ChannelUsage { amount_msat: 768, ..usage }; - assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 916); + assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 921); let usage = ChannelUsage { amount_msat: 896, ..usage }; assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), u64::max_value()); @@ -2919,7 +2937,7 @@ mod tests { assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 300); SinceEpoch::advance(Duration::from_secs(10)); - assert_eq!(deserialized_scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 365); + assert_eq!(deserialized_scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 370); } #[test] @@ -3146,7 +3164,7 @@ mod tests { assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 47); assert_eq!(scorer.historical_estimated_channel_liquidity_probabilities(42, &target), None); - assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, 42), + assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, 42, ¶ms), None); scorer.payment_path_failed(&payment_path_for_amount(1), 42); @@ -3157,9 +3175,9 @@ mod tests { assert_eq!(scorer.historical_estimated_channel_liquidity_probabilities(42, &target), Some(([32, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 32, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]))); - assert!(scorer.historical_estimated_payment_success_probability(42, &target, 1) + assert!(scorer.historical_estimated_payment_success_probability(42, &target, 1, ¶ms) .unwrap() > 0.35); - assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, 500), + assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, 500, ¶ms), Some(0.0)); // Even after we tell the scorer we definitely have enough available liquidity, it will @@ -3174,11 +3192,11 @@ mod tests { // The exact success probability is a bit complicated and involves integer rounding, so we // simply check bounds here. let five_hundred_prob = - scorer.historical_estimated_payment_success_probability(42, &target, 500).unwrap(); + scorer.historical_estimated_payment_success_probability(42, &target, 500, ¶ms).unwrap(); assert!(five_hundred_prob > 0.66); assert!(five_hundred_prob < 0.68); let one_prob = - scorer.historical_estimated_payment_success_probability(42, &target, 1).unwrap(); + scorer.historical_estimated_payment_success_probability(42, &target, 1, ¶ms).unwrap(); assert!(one_prob < 1.0); assert!(one_prob > 0.95); @@ -3190,7 +3208,7 @@ mod tests { // data entirely instead. assert_eq!(scorer.historical_estimated_channel_liquidity_probabilities(42, &target), None); - assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, 1), None); + assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, 1, ¶ms), None); let mut usage = ChannelUsage { amount_msat: 100, @@ -3354,7 +3372,7 @@ mod tests { assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage, ¶ms), 0); assert_eq!(scorer.historical_estimated_channel_liquidity_probabilities(42, &target), None); - assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, 42), + assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, 42, ¶ms), None); // Fail to pay once, and then check the buckets and penalty. @@ -3369,14 +3387,14 @@ mod tests { Some(([32, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 32, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]))); // The success probability estimate itself should be zero. - assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, amount_msat), + assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, amount_msat, ¶ms), Some(0.0)); // Now test again with the amount in the bottom bucket. amount_msat /= 2; // The new amount is entirely within the only minimum bucket with score, so the probability // we assign is 1/2. - assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, amount_msat), + assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, amount_msat, ¶ms), Some(0.5)); // ...but once we see a failure, we consider the payment to be substantially less likely, @@ -3386,7 +3404,7 @@ mod tests { assert_eq!(scorer.historical_estimated_channel_liquidity_probabilities(42, &target), Some(([63, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [32, 31, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]))); - assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, amount_msat), + assert_eq!(scorer.historical_estimated_payment_success_probability(42, &target, amount_msat, ¶ms), Some(0.0)); } }