loss of sync peer candidates, max peers reached

[raedah]

[WRN] BMGR: No sync peer candidates available

[INF] SRVR: Max peers reached [125] - disconnecting peer x.x.x.x:x (inbound)

Not sure what triggered the above conditions, but these both show in the log and dcrd was not able to recover until manually restarted.

[davecgh]

Thanks for the report. It's the first time I've seen it in nearly a decade, but I do understand how it can theoretically happen.

[ukane-philemon]

@davecgh pls can you throw more light on how it can theoretically happen?

[davecgh]

Essentially, there isn't explicit handling to 100% prevent it from happening, so that makes it possible even though the probability is extremely low such that it essentially almost never happens. I should also note that it eventually will recover when some of the existing peers disconnect, but that could take a while since peers are not ordinarily disconnected without an explicit reason which could make it seem like it couldn't recover automatically.

All of that said, the final outstanding part of #1145 gets rid of the entire notion of a sync peer and thus will resolve it indirectly too.