Poor route selection

[rkfg]

Just had a situation yesterday when Blixt couldn't send a payment because of no liquidity on the route (and I repeated it 3 times after timeouts) while SBW did it in just two attempts (≈2 seconds). Background:

• I have Blixt connected to my own node via a private channel
• the payment was to WalletOfSatoshi node using a static LNURL QR
• I monitored the attempts on my node with lntop
• the amount was quite small, 10k sats

The attempts went fine through my node (no link failure), they failed somewhere later on the route. After about 10 attempts the payment fails due to timeout, I tried again and then again without success. The total number of attempts should be close to 30. Then I started SBW (also connected to my own node via a private channel), scanned the same code, entered the same amount and from the lntop log I saw this:

• SBW tried to pay using my direct channel to WoS which was drained down to the reserved limit, it failed
• SBW then tried to pay through ACINQ with higher fee and succeeded

I know that the LN implementation in SBW is different and doesn't use lnd unlike Blixt. Probably it has different priorities for fee selection so it can sacrifice a few sats to make the payment faster and Blixt tries to save on fees but it results in very poor UX. There's a time_pref parameter in lnd 0.15.0, maybe it can help with this after your version is updated. Or something else can be tweaked to prefer more reliable paths instead of the cheapest ones. In my case the difference was just 5 sats when paid by SBW and Blixt tried to get 0 or 2 at most. I don't think 5 sats are worth the trouble when the wallet doesn't do its primary job.

[djkazic]

I can't actually just increase the limit like that.

The amount of data accumulates at about 1MB/hr for the patch. So at 50 hours of diff you actually are better off doing a full download.

[rkfg]

Ooh, good to know! Didn't expect it to be this big.