[Bitcoin-development] Proposed alternatives to the 20MB step function

Cameron Garnham da2ce7 at gmail.com
Sat May 30 01:36:39 UTC 2015


First off, I am glad that the idea of dynamic block size adjustment is
gaining some attention, in particular the model that I proposed.

I wanted to take some time and explain some of the philosophy of how,
and why, I proposed this this particular model.

When Bitcoin was first made, there was a 32MB block size limit; this
was quickly found to be open to spam (and potentially DOS, as the code
was not-at-all optimized to support large blocks), and was reduced to
1MB, this was a quick fix that was never intended to last; at some
point the network should come to an understanding, a consensus if you
will, of what (and how much) belongs in a block.
The core point of this is that miners have always, and will always;
hold the power, to decide what goes into blocks; this implicitly,
obviously, includes how large blocks are. Miners are able to come any
sort of agreement they wish, providing the bitcoin clients accept
their blocks as valid.

Say if Satoshi never decided to place the 1MB block limit: It would be
up to the miners to decide what they consider a ‘reasonable’ block is.
However, they would need to find some way to communicate this and
reach an agreement; some protocol.  They, say, could have done this
informally on what is now the bitcointalk forum, or used Twitter.
However, what they really need is indeed a "consensus protocol". Some
simple terms to define what is acceptable and what is not.

Hence, the proposal introducing a consensus protocol for block sizes;
instead of just having a hard limit (enforced by everyone), instead,
we have a constant factor above the average block size over a fixed
intervals that is soft-forked by only the miners. (The next simplest
mathematical construct).
This proposal is entirely a soft-fork and may be implemented without
changing any client code what so ever. In-fact, it could be
implemented by only a simple 51% majority of miners, with-or-without
gaining the wider community consensus. (Assuming that the 1MB block
size rule still applies).
The nice thing about this is that it really is impossible to stop,
for-example, if pre-relaying of block headers is implemented; the
miners could always soft-fork to include the block-size in the
coinbase. The only reason that the miners have not done this yet, is
that there has not yet been a strong will to increase transaction fees.

If we assume the miners will operate in a way to collectively maximize
profit; then we can assume they will not try to maximize utility of
the network (having as many transactions as possible), rather have as
few transactions as the total economy can support the cost.  Meaning
that limiting to much smaller blocks will probably be much more
profitable than having large blocks.

Since there is no requirement for the clients to know about the block
size consensus protocol, this truly can be a
‘bi-directional-soft-fork’, in that the miners can choose to change
the rules at any time, with only a simple 51% majority. Therefore, any
parameters that we pick are always up for debate.

Why the 1.5x over 2016 blocks? -  Using some game theory, and
deduction: I wished to pick the type of agreement that would be
natural for the miners to come to (selfishly).

First, Why 1.5x, this means that only a super-majority of miners can
easily increase the block size. – There is no natural incentive for
miners to produce large blocks that have very few fees.

Second, Why 2016 blocks for adjusting the average:  Miners HATE
unpredictability, for shorter time periods the miner will need to have
infrastructure ready to support potentially much larger block almost
immediately. 2016 blocks is a period that the miners are already well
used to, meaning that it will take slightly less than a month for
blocks of double size to be permitted.

This entire infrastructure can be implemented without needing to
update any clients; once implemented, tested, solid, and well accepted
by the (mining) community then we can revisit increasing the 1M hard
limit. (If we still have demand for it, maybe the average block size
will reduce to say, 100KB).


Cam.






> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256
> 
> While being in the Bitcoin community for a long time, I haven't
> been so directly involved in the development.  However I wish to
> suggest a different pre-hard-fork soft-fork approach:
> 
> 
> Set a 'block size cap' in the similar same way as we set
> difficulty.
> 
> Every 2016 blocks take the average size of the blocks and multiply
> the size by 1.5x, rejecting blocks that are larger than this size,
> for the next 2016 period.
> 
> I would of-course suggest that we keep the limits at min 100kb and
> max (initially) 990kb (not 1mb on purpose, as this should become
> the new limit), rounding up to the nearest 10kb.
> 
> A: we don't have pressure at the 1mb limit, (we reduce the limit in
> a flexible manner to 990kb).
> 
> B: we can upgrade the network to XYZ hard-limit, then slowly raze
> the soft-limit after being sure the network, as-a-whole is ready.
> 
> If we on-day remove the block-size limit, this rule will stop a
> rouge miner from making 10mb, or 100mb blocks, or 1gb blocks.
> 
> This could be implemented by the miners without breaking any of
> the clients, and would tend to produce a better dynamic fee
> pressure.
> 
> 
> This will give the mechanics to the miners to create consensus to 
> agree what block-sizes they believe are best for the network, and 
> allows the block-sizes to dynamically grow in response to larger
> demand.
> 
> 
> 
> On 5/8/2015 10:35 AM, Pieter Wuille wrote:
>> On May 7, 2015 3:08 PM, "Roy Badami" <roy at gnomon.org.uk> wrote:
>>> 
>>> On Thu, May 07, 2015 at 11:49:28PM +0200, Pieter Wuille wrote:
>>>> I would not modify my node if the change introduced a
>>>> perpetual 100 BTC subsidy per block, even if 99% of miners
>>>> went along with it.
>>> 
>>> Surely, in that scenario Bitcoin is dead.  If the fork you
>>> prefer has only 1% of the hash power it is trivially vulnerably
>>> not just to a 51% attack but to a 501% attack, not to mention
>>> the fact that you'd only be getting one block every 16 hours.
>> 
>> Yes, indeed, Bitcoin would be dead if this actually happens. But 
>> that is still where the power lies: before anyone (miners or 
>> others) would think about trying such a change, they would need
>> to convince people and be sure they will effectively modify
>> their code.
>> 
>> 
>> 
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