On Aug 11, 2015 12:11 AM, "Sergio Demian Lerner" <sergio.d.lerner@gmail.com> wrote:
> What I'm saying is that this ratio may have improved 20x since miners began using the TheBlueMatt relay network, so deteriorating the ratio 2x does not put miners in a unknown future, but in an future which is far better than the state they were a year ago.

It's still worse than doubling the block size, which was your main argument.

> But SPV mining has improved the ratio another 2x (because headers can be pushed even faster, fit in a single network packet, and can do without inv/getdata round-trips because they basically "pay" for the bandwidth usage by its own proof of work). 
> With a better wire protocol you can "propagate" a 10 MB block faster that the time it takes currently to propagate an empty block. 
> So 10x deterioration of the ratio would be still something acceptable.

So yes, better relay protocols (whether you consider "SPV mining" a form of that or not) reduce the effect of the block size. That does not give any benefit for reduced interblock times.

Your argument seems to be "centralization pressure is not bad now, because it already improved a lot... so we can make it worse again by reducing interblock time"? I disagree that it is not bad, and shorter blocks have other downsides which were already mentioned.

>> Also, you seem to consider SPV mining a good thing?
>
> I'm not saying it's a good thing. I'm saying that it's impossible to avoid. It's a real incentive. It must exists so Bitcoin is incentive compatible. We can talk for hours and hours and we won't prevent miners from doing it. I predicted it back in 2013, without even being a miner myself. It's here to stay. Forever. It's a pity Greg chose that awful name of "SPV" mining instead some cool name like "Instant" mining that we could market as Bitcoin latest feature :)

>> It requires trust between miners that know eachother, and fundamentally breaks the security assumption of SPV clients...
>
> No is does not.

The SPV security assumption is that no hashrate majority will collude in order to make my transactions incorrectly look confirmed.

With validation-less mining, even a 0.1% hashrate that is part of a group with 60% hashrate is enough to make that happen.

Of course they won't intentionally do that. No other miner would agree to do validation-less mining with them again, making it harder for them to compete. So it is not permissionless: you get higher profitability by making an agreement with the largest hashrate. I think that is a much worse centralization effect than having an optional centralized relay network available... there could even be multiple such networks.

> The incentive follows directly from the cheating cost (the subsidy). Even if I don't know you, I know you wouldn't waste 25 BTC to try to cheat me for 25 BTC with a probability of 1/100, that's for sure. On average, you loose 24.75 BTC per cheat attempt.

Per cheat attempt, or per bug.

> SPV mining incentive will stay until there is no subsidy, as many other incentives. SPV mining also must be there to prevent malicious actors from DoS-ing the relay network. If it's there, then the DoS incentive disappears.
>
> Let's code "instant" mining into Bitcoin Core, and do it right.

I thought about this too. Since headers-first it would be trivial to do: if our best header is ahead of our best block, hand out an empty template in createblocktemplate, and we're done.

Unfortunately, Greg Maxwell pointed out that this (even with a time limit) amplifies selfish mining, since I can propagate headers before propagating blocks, in order to make others temporarily work on top of my chain.

> Also as Michael Rudy points out, higher block rate means lower variance, and that's good for miners. Last, as I already said, having a lower average block interval strengthens Bitcoin value proposition, so miners would be delighted that their bitcoins are more worthy.

Only a small constant factor, but yes.

--
Pieter