routing: add proportional attempt cost

lnrpc/routerrpc/config.go

@@ -47,6 +47,7 @@ func DefaultConfig() *Config {
 		MinRouteProbability:   routing.DefaultMinRouteProbability,
 		PenaltyHalfLife:       routing.DefaultPenaltyHalfLife,
 		AttemptCost:           routing.DefaultAttemptCost.ToSatoshis(),
+		AttemptCostPPM:        routing.DefaultAttemptCostPPM,
 		MaxMcHistory:          routing.DefaultMaxMcHistory,
 	}
 
@@ -62,6 +63,7 @@ func GetRoutingConfig(cfg *Config) *RoutingConfig {
 		AprioriWeight:         cfg.AprioriWeight,
 		MinRouteProbability:   cfg.MinRouteProbability,
 		AttemptCost:           cfg.AttemptCost,
+		AttemptCostPPM:        cfg.AttemptCostPPM,
 		PenaltyHalfLife:       cfg.PenaltyHalfLife,
 		MaxMcHistory:          cfg.MaxMcHistory,
 	}

lnrpc/routerrpc/routing_config.go

@@ -32,7 +32,13 @@ type RoutingConfig struct {
 	// AttemptCost is the fixed virtual cost in path finding of a failed
 	// payment attempt. It is used to trade off potentially better routes
 	// against their probability of succeeding.
-	AttemptCost btcutil.Amount `long:"attemptcost" description:"The (virtual) cost in sats of a failed payment attempt"`
+	AttemptCost btcutil.Amount `long:"attemptcost" description:"The fixed (virtual) cost in sats of a failed payment attempt"`
+
+	// AttemptCostPPM is the proportional virtual cost in path finding of a
+	// failed payment attempt. It is used to trade off potentially better
+	// routes against their probability of succeeding. This parameter is
+	// expressed in parts per million of the total payment amount.
+	AttemptCostPPM int64 `long:"attemptcostppm" description:"The proportional (virtual) cost in sats of a failed payment attempt expressed in parts per million of the total payment amount"`
 
 	// MaxMcHistory defines the maximum number of payment results that
 	// are held on disk by mission control.

routing/pathfind.go

@@ -45,11 +45,23 @@ type pathFinder = func(g *graphParams, r *RestrictParams,
 	[]*channeldb.ChannelEdgePolicy, error)
 
 var (
-	// DefaultAttemptCost is the default virtual cost in path finding of a
+	// DefaultAttemptCost is the default fixed virtual cost in path finding
-	// failed payment attempt. It is used to trade off potentially better
+	// of a failed payment attempt. It is used to trade off potentially
-	// routes against their probability of succeeding.
+	// better routes against their probability of succeeding.
 	DefaultAttemptCost = lnwire.NewMSatFromSatoshis(100)
 
+	// DefaultAttemptCostPPM is the default proportional virtual cost in
+	// path finding weight units of executing a payment attempt that fails.
+	// It is used to trade off potentially better routes against their
+	// probability of succeeding. This parameter is expressed in parts per
+	// million of the payment amount.
+	//
+	// It is impossible to pick a perfect default value. The current value
+	// of 0.1% is based on the idea that a transaction fee of 1% is within
+	// reasonable territory and that a payment shouldn't need more than 10
+	// attempts.
+	DefaultAttemptCostPPM = int64(1000)
+
 	// DefaultMinRouteProbability is the default minimum probability for routes
 	// returned from findPath.
 	DefaultMinRouteProbability = float64(0.01)
@@ -314,11 +326,17 @@ type RestrictParams struct {
 // PathFindingConfig defines global parameters that control the trade-off in
 // path finding between fees and probabiity.
 type PathFindingConfig struct {
-	// AttemptCost is the virtual cost in path finding of a failed
+	// AttemptCost is the fixed virtual cost in path finding of a failed
 	// payment attempt. It is used to trade off potentially better routes
 	// against their probability of succeeding.
 	AttemptCost lnwire.MilliSatoshi
 
+	// AttemptCostPPM is the proportional virtual cost in path finding of a
+	// failed payment attempt. It is used to trade off potentially better
+	// routes against their probability of succeeding. This parameter is
+	// expressed in parts per million of the total payment amount.
+	AttemptCostPPM int64
+
 	// MinProbability defines the minimum success probability of the
 	// returned route.
 	MinProbability float64
@@ -548,6 +566,14 @@ func findPath(g *graphParams, r *RestrictParams, cfg *PathFindingConfig,
 	// if the cltv limit is MaxUint32.
 	absoluteCltvLimit := uint64(r.CltvLimit) + uint64(finalHtlcExpiry)
 
+	// Calculate the absolute attempt cost that is used for probability
+	// estimation.
+	absoluteAttemptCost := int64(cfg.AttemptCost) +
+		int64(amt)*cfg.AttemptCostPPM/1000000
+
+	log.Debugf("Pathfinding absolute attempt cost: %v sats",
+		float64(absoluteAttemptCost)/1000)
+
 	// processEdge is a helper closure that will be used to make sure edges
 	// satisfy our specific requirements.
 	processEdge := func(fromVertex route.Vertex,
@@ -642,7 +668,7 @@ func findPath(g *graphParams, r *RestrictParams, cfg *PathFindingConfig,
 		// probability.
 		tempDist := getProbabilityBasedDist(
 			tempWeight, probability,
-			int64(cfg.AttemptCost),
+			absoluteAttemptCost,
 		)
 
 		// If there is already a best route stored, compare this

routing/pathfind_test.go

@@ -2467,9 +2467,9 @@ func TestProbabilityRouting(t *testing.T) {
 		// to the same total route probability. In both cases the three
 		// hop route should be the best route. The three hop route has a
 		// probability of 0.5 * 0.8 = 0.4. The fee is 5 (chan 10) + 8
-		// (chan 11) = 13. Path finding distance should work out to: 13
+		// (chan 11) = 13. The attempt cost is 9 + 1% * 100 = 10. Path
-		// + 10 (attempt penalty) / 0.4 = 38. The two hop route is 25 +
+		// finding distance should work out to: 13 + 10 (attempt
-		// 10 / 0.7 = 39.
+		// penalty) / 0.4 = 38. The two hop route is 25 + 10 / 0.7 = 39.
 		{
 			name: "three hop 1",
 			p10:  0.8, p11: 0.5, p20: 0.7,
@@ -2485,6 +2485,21 @@ func TestProbabilityRouting(t *testing.T) {
 			amount:         100,
 		},
 
+		// If a larger amount is sent, the effect of the proportional
+		// attempt cost becomes more noticeable. This amount in this
+		// test brings the attempt cost to 9 + 1% * 300 = 12 sat. The
+		// three hop path finding distance should work out to: 13 + 12
+		// (attempt penalty) / 0.4 = 43. The two hop route is 25 + 12 /
+		// 0.7 = 42. For this higher amount, the two hop route is
+		// expected to be selected.
+		{
+			name: "two hop high amount",
+			p10:  0.8, p11: 0.5, p20: 0.7,
+			minProbability: 0.1,
+			expectedChan:   20,
+			amount:         300,
+		},
+
 		// If the probability of the two hop route is increased, its
 		// distance becomes 25 + 10 / 0.85 = 37. This is less than the
 		// three hop route with its distance 38. So with an attempt
@@ -2589,7 +2604,8 @@ func testProbabilityRouting(t *testing.T, paymentAmt btcutil.Amount,
 	}
 
 	ctx.pathFindingConfig = PathFindingConfig{
-		AttemptCost:    lnwire.NewMSatFromSatoshis(10),
+		AttemptCost:    lnwire.NewMSatFromSatoshis(9),
+		AttemptCostPPM: 10000,
 		MinProbability: minProbability,
 	}
 

sample-lnd.conf

@@ -619,8 +619,12 @@ litecoin.node=ltcd
 ; probability (default: 1h0m0s)
 ; routerrpc.penaltyhalflife=2h                            
 
-; The (virtual) cost in sats of a failed payment attempt (default: 100)
+; The (virtual) fixed cost in sats of a failed payment attempt (default: 100)
-; routerrpc.attemptcost=90                                
+; routerrpc.attemptcost=90     
+
+; The (virtual) proportional cost in ppm of the total amount of a failed payment
+; attempt (default: 1000)
+; routerrpc.attemptcostppm=900
 
 ; The maximum number of payment results that are held on disk by mission control
 ; (default: 1000)

server.go

@@ -724,14 +724,16 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 	}
 
 	srvrLog.Debugf("Instantiating payment session source with config: "+
-		"AttemptCost=%v, MinRouteProbability=%v",
+		"AttemptCost=%v + %v%%, MinRouteProbability=%v",
 		int64(routingConfig.AttemptCost),
+		float64(routingConfig.AttemptCostPPM)/10000,
 		routingConfig.MinRouteProbability)
 
 	pathFindingConfig := routing.PathFindingConfig{
 		AttemptCost: lnwire.NewMSatFromSatoshis(
 			routingConfig.AttemptCost,
 		),
+		AttemptCostPPM: routingConfig.AttemptCostPPM,
 		MinProbability: routingConfig.MinRouteProbability,
 	}