The download from a peer is now limited to just 4000 blocks, at which
point the download proceeds from another peer.
Naturally it can go back to the first afterwards too.
The idea is that we download a month worth of blocks at a time and then
fetch the same blocks from a backup peer in order to be certain we
actually see the real state.
The problem we've seen is that after the first downloads we end up
starting the second and if the initial sync or a similar large download
happens, many people won't leave it running until the backup actually
completes since the UI looks like its finished.
This is also a good starting point for rating peers at download speed by
having predictable chunks and that means we could time and aim to use
the faster peers.
This is becoming relevant as we can see a huge difference where peers
give you 10x performance compared to some of the slower ones.
tomFlowee
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