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plugins/libplugin-pay.c: Round-robin routehints when splitting.

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This improves the success rate of `test_mpp_interference_2`, though
still not quite up to the level that we can remove `@flaky` from it.
This commit is contained in:
ZmnSCPxj jxPCSnmZ
2020-08-11 17:29:08 +08:00
committed by Rusty Russell
parent ba3f38077e
commit 128adf0938
2 changed files with 48 additions and 6 deletions
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38
plugins/libplugin-pay.c
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@@ -2021,8 +2021,8 @@ static struct route_info *next_routehint(struct routehints_data *d,
* - MUST specify the most-preferred field first, followed
* by less-preferred fields, in order.
*/
for (; d->offset <numhints; d->offset++) {
curr = d->routehints[d->offset];
for (; d->offset < numhints; d->offset++) {
curr = d->routehints[(d->base + d->offset) % numhints];
if (curr == NULL || !routehint_excluded(p, curr))
return curr;
}
@@ -2269,18 +2269,50 @@ static struct routehints_data *routehint_data_init(struct payment *p)
d->routehints = pd->routehints;
pd = payment_mod_routehints_get_data(p->parent);
if (p->parent->step == PAYMENT_STEP_RETRY) {
d->base = pd->base;
d->offset = pd->offset;
/* If the previous try failed to route, advance
* to the next routehint. */
if (!p->parent->route)
++d->offset;
} else
} else {
size_t num_routehints = tal_count(d->routehints);
d->offset = 0;
/* This used to be pseudorand.
*
* However, it turns out that using the partid for
* this payment has some nice properties.
* The partid is in general quite random, due to
* getting entropy from the network on the timing
* of when payments complete/fail, and the routehint
* randomization is not a privacy or security feature,
* only a reliability one, thus does not need a lot
* of entropy.
*
* But the most important bit is that *splits get
* contiguous partids*, e.g. a presplit into 4 will
* usually be numbered 2,3,4,5, and an adaptive split
* will get two consecutive partid.
* Because of the contiguity, using the partid for
* the base will cause the split-up payments to
* have fairly diverse initial routehints.
*
* The special-casing for <= 2 and the - 2 is due
* to the presplitter skipping over partid 1, we want
* the starting splits to have partid 2 start at
* base 0.
*/
if (p->partid <= 2 || num_routehints <= 1)
d->base = 0;
else
d->base = (p->partid - 2) % num_routehints;
}
return d;
} else {
/* We defer the actual initialization of the routehints array to
* the step callback when we have the invoice attached. */
d->routehints = NULL;
d->base = 0;
d->offset = 0;
return d;
}