Raise fallback fee rate from 10 sat/vB to 20 sat/vB

[kristapsk]

It's just current reality on mainnet, that's around what bitcoin-cli estimatesmartfee 1008 (1 week confirmation target) returns.

[AdamISZ]

utACK 9c13180

I can't see any way to arrive at an objectively correct number here (I guess we could try to gather data about typical mempool ejection rates over time? but as we know there is no "the mempool", so ...), but it's hard to argue that the legacy value of 10k is indeed too low, nowadays.

[kristapsk]

I can't see any way to arrive at an objectively correct number here (I guess we could try to gather data about typical mempool ejection rates over time? but as we know there is no "the mempool", so ...), but it's hard to argue that the legacy value of 10k is indeed too low, nowadays.

I think best we could do currently is to adjust the number before each release. 20 sat/vB is conservative number, besides we used to have 10 sat/vB fallback when 1 sat/vB were confirming often.