estimatesmartfee only works for target>16 (testnet) #14431

Core Version: 0.16.3. Network: TestNet.

The node is running for a few days now, and was serving targets 2-15 properly. Now, I noticed estimatesmartfee fails for any targets under 16. So, there's two abnormalities here:

• estimatesmartfee was working, but started failing later on
• estimatesmartfee only fails for targets < 16

Are any of these intended behaviors?

I've witnessed this behavior on testnet too, although was running a 0.17 node and it was a bit higher than 16 for me.

I haven't done any investigation, so I'm shooting blind -- but in my case I wonder if it was something to do with resuming from an extended sleep? At first it was working (maybe it reading a cached fee rate?) and then after a while it invalidated that without knowing the actual fee rate?

For the record a few hours later when I checked, it was estimating fees from target 9 properly. A day later it was estimating properly from target 3. And I checked now (3 days later) and it is estimating fees properly for everything. So the 16 I reported is not a magic number.

I wonder if it was something to do with resuming from an extended sleep

In my case it wasn't that. bitcoind was running for days on a server, while estimating fees properly, because I prevent even from starting my own server application until feerates for target 2 are not available.

I suspect this is just related to the low tx volume on testnet, and the affected targets likely vary. I think the estimates are based on fee rate buckets, and it seems possible that some of the buckets are totally empty at times, and this prevents proper estimation. A slightly educated guess.

@nopara73 have you retested this with more modern versions and experienced similar behavior?

I haven't encounter this lately. Gonna reopen if I do.