[bitcoin-dev] Adjusted difficulty depending on relative blocksize

[Anthony Towns]

On 14 August 2015 at 16:48, Jakob Rönnbäck <
bitcoin-dev at lists.linuxfoundation.org> wrote:

> 14 aug 2015 kl. 16:20 skrev Anthony Towns <aj at erisian.com.au>:
>
> On 14 August 2015 at 11:59, Jakob Rönnbäck <
> bitcoin-dev at lists.linuxfoundation.org> wrote:
>
>> What if one were to adjust the difficulty (for individual blocks)
>> depending on the relative size to the average block size of the previous
>> difficulty period? (I apologize if i’m not using the correct terms, I’m not
>> a real programmer, and I’ve only recently started to subscribe to the
>> mailing list)
>>
>
> ​That would mean that as usage grew, blocksize could increase, but
> confirmation times would also increase (though presumably less than
> linearly). That seems like a loss?
>
> Would that really be the case though? If it takes 5% to find a block, but
> it contains 5% more transactions would that not mean it’s the same? That
> would argue against the change if not for the fact that the blocks will be
> bigger for the next difficulty period.
>

​If you're waiting for one confirmation, something like that works -- you
might from 95% chance of 10 minutes 5% chance of 20 minutes to 100% chance
of 10m30s. But if you want 144 confirmations (eg) you go from 95% chance of
1 day, 5% chance of 1 day 10 minutes; to 100% chance of 1 day 72 minutes.

> If you also let the increase in confirmation time (due to miners finding
> harder blocks rather than a reduction in hashpower) then get reflected back
> as decreased difficulty, it'd probably be simpler to just dynamically
> adjust the max blocksize wouldn't it?
>
> I guess that could make the difficulty fluctuate a bit depending on the
> amount of transactions and the fees being paid. Would it really matter in
> the long run though? Since it’s the same amount of miners, doesn’t that
> just mean it’s just the number that is lower, not the actual investment
> needed to mine the blocks? Not sure if this would open up some forms of
> attacks on the system for someone willing to lose money though…
>

Once blocksizes had normalised as much larger than 1MB with a corresponding
higher average hashrate, a bad actor could easily mine a raft of valid
empty/small blocks at the minimum hash rate and force a reorg (and do
doublespends, etc).

​Cheers,
aj​

-- 
Anthony Towns <aj at erisian.com.au>
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