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pay: Use log probability based bias in channel selection

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Changelog-Changed: pay: The route selection will now use the log-propability-based channel selection to increase success rate and reduce time to completion
This commit is contained in:
Rene Pickhardt
2021-10-04 15:30:29 +02:00
committed by Christian Decker
parent 233d339061
commit 0ba1bc30fe
1 changed files with 11 additions and 14 deletions
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25
plugins/libplugin-pay.c
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@@ -8,6 +8,7 @@
#include <common/random_select.h> #include <common/random_select.h>
#include <common/type_to_string.h> #include <common/type_to_string.h>
#include <errno.h> #include <errno.h>
#include <math.h>
#include <plugins/libplugin-pay.h> #include <plugins/libplugin-pay.h>
#include <sys/types.h> #include <sys/types.h>
#include <wire/peer_wire.h> #include <wire/peer_wire.h>
@@ -707,22 +708,15 @@ static u64 capacity_bias(const struct gossmap *map,
int dir, int dir,
struct amount_msat amount) struct amount_msat amount)
{ {
struct amount_msat fee;
struct amount_sat capacity; struct amount_sat capacity;
u64 capmsat, amtmsat = amount.millisatoshis; /* Raw: lengthy math */
/* Median fees are 1000 base, 10 ppm, so scale capacity bias to that */
/* Overflow is pretty-much impossible, so ignore. */
if (!amount_msat_fee(&fee, amount, 1000, 10))
return 0;
/* Can fail in theory if gossmap changed underneath. */ /* Can fail in theory if gossmap changed underneath. */
if (!gossmap_chan_get_capacity(map, c, &capacity)) if (!gossmap_chan_get_capacity(map, c, &capacity))
return 0; return 0;
/* bias = fee * (amt / (c + 1)) */ capmsat = capacity.satoshis * 1000; /* Raw: lengthy math */
return fee.millisatoshis /* Raw: complex math & laziness */ return -log((capmsat + 1 - amtmsat) / (capmsat + 1));
* amount.millisatoshis /* Raw: complex math & laziness */
/ (capacity.satoshis*1000 + 1); /* Raw: complex math & laziness */
} }
/* Prioritize costs over distance, but bias to larger channels. */ /* Prioritize costs over distance, but bias to larger channels. */
@@ -732,10 +726,13 @@ static u64 route_score(u32 distance,
int dir, int dir,
const struct gossmap_chan *c) const struct gossmap_chan *c)
{ {
u64 costs = cost.millisatoshis + risk.millisatoshis /* Raw: score */ u64 cmsat = cost.millisatoshis; /* Raw: lengthy math */
/* We use global_gossmap (can't still be NULL) u64 rmsat = risk.millisatoshis; /* Raw: lengthy math */
* *without* get_gossmap() which might change topology. */ u64 bias = capacity_bias(global_gossmap, c, dir, cost);
+ capacity_bias(global_gossmap, c, dir, cost);
/* Smoothed harmonic mean to avoid division by 0 */
u64 costs = (cmsat * rmsat * bias) / (cmsat + rmsat + bias + 1);
if (costs > 0xFFFFFFFF) if (costs > 0xFFFFFFFF)
costs = 0xFFFFFFFF; costs = 0xFFFFFFFF;
return costs; return costs;