Re: [bitcoin-dev] Miners are struggling with blocks far smaller than 750KB blocks and resorting to SPV mining

From: Timo Hanke <timo.hanke@web•de>
To: Luv Khemani <luvb@hotmail•com>
Cc: bitcoin-dev@lists•linuxfoundation.org
Subject: Re: [bitcoin-dev] Miners are struggling with blocks far smaller than 750KB blocks and resorting to SPV mining
Date: Thu, 20 Aug 2015 16:27:20 +0200	[thread overview]
Message-ID: <CAF3fmD4Du9Pc3y6Y6NKGxTiYFe03f6fnCWBvy-qXSLAqGd8prw@mail.gmail.com> (raw)
In-Reply-To: <BLU172-W10F7A109C917CD56E7DF4DC2790@phx.gbl>

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That's not a valid conclusion. Just because you observe a miner producing
empty blocks doesn't mean he is SPV mining.

There can be many reasons for mining on an empty block even after having
fully verified the previous block. And therefore these reasons would be
completely independent of block size. You cannot conclude that miners are
struggling with a certain block size.

For example, there are reasons rooted in the mining hardware and mining
software itself, which have nothing to do with the node software, in
particular not with block propagation, verification or transaction
selection. See also https://github.com/BlockheaderNonce2/bitcoin/wiki where
this was warned about. The effect can be expected to become more pronounced
in the future.

Timo

On Mon, Aug 17, 2015 at 10:42 AM, Luv Khemani via bitcoin-dev <
bitcoin-dev@lists•linuxfoundation.org> wrote:

> Hi all,
>
>   I previously mentioned in a post that i believe that technically nodes
> are capable of handling blocks an order of magnitude larger than the
> current blocksize limit, the only missing thing was an incentive to run
> them. I have been monitoring the blockchain for the past couple of weeks
> and am seeing that even miners who have all the incentives are for whatever
> reason struggling to download and validate much smaller blocks.
>
> The data actually paints a very grim picture of the current
> bandwidth/validating capacity of the global mining network.
>
> See the following empty blocks mined despite a non-trivial elapsed time
> from the previous block just from the past couple of days alone (Data from
> insight.bitpay.com):
>
> EmptyBlock /Time since previous block/ Size of previous block(bytes)/Mined
> by
> ====================================================
> 370165  29s  720784  Antpool
> 370160  31s  50129    BTCChinaPool
> 370076  49s  469988  F2Pool
> 370059  34s  110994  Antpool
> 370057  73s  131603  Antpool
>
> We have preceding blocks as small as 50KB with 30s passing and the miner
> continues to mine empty blocks via SPV mining.
> The most glaring case is Block 370057 where despite 73s elapsing and the
> preceding block being a mere 131KB, the miner is unable to
> download/validate fast enough to include transactions in his block. Unless
> ofcourse the miner is mining empty blocks on purpose, which does not make
> sense as all of these pools do mine blocks with transactions when the
> elapsed time is greater.
>
> This is a cause for great concern, because if miners are SPV mining for a
> whole minute for <750KB blocks, at 8MB blocks, the network will just fall
> apart as a significant portion of the hashing power SPV mines throughout.
> All a single malicious miner has to do is mine an invalid block on purpose,
> let these pools SPV mine on top of them while it mines a valid block free
> of their competition. Yes, these pools deserve to lose money in that event,
> but the impact of reorgs and many block orphans for anyone not running a
> full node could be disastrous, especially more so in the XT world where
> Mike wants everyone to be running SPV nodes. I simply don't see the XT fork
> having any chance of surviving if SPV nodes are unreliable.
>
> And if these pools go out of business, it will lead to even more mining
> centralization which is already too centralized today.
>
> Can anyone representing these pools comment on why this is happening? Are
> these pools on Matt's relay network?
>
>
>
>
>
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>
>

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