[bitcoin-dev] Dynamically Controlled Bitcoin Block Size Max Cap

Rodney Morris rodney.morris at gmail.com
Mon Aug 17 11:57:47 UTC 2015

Words cannot capture how much I wish Satoshi had put logic like this (or
even just a simple block size doubling every reward halving) in place when
he put in the "temporary" 1MB anti-spam block size limit...

I see problems to this approach.  The biggest one I see is that a miner
with 11% of hash power could sabotage block size increases by only ever
mining empty blocks.

I haven't run any statistics or simulations, but I'm concerned that the
interplay between the random distribution of transaction arrival and the
random distribution of block times may lead to false signals.

A 90% full block 1 minute after the previous block is a more "serious"
problem than a 90% full block 30 minutes after the previous block.  A 90%
full block after a 90% full block is a more "serious" problem than a 90%
full block after an empty block.

I would expect a robust approach in this manner to look at block sizes
weighted by block times, but this is an interesting proposal regardless.

But I think you'll run up against one of the great schisms in this debate -
those that believe blocks should always be full (or close to it), to
encourage a "fee market" and to encourage off-chain transactions, and those
that think that the blockchain should be useable by almost anyone for
almost anything, implying there should always be spare space in blocks,
with off-chain transactions reserved for microtransactions and zero-conf
(and possibly low-fee transactions).  At least, that's my take on it.


> Date: Mon, 17 Aug 2015 11:51:26 +0100
> From: Btc Drak <btcdrak at gmail.com>
> To: Patrick Strateman <patrick.strateman at gmail.com>
> Cc: Bitcoin Dev <bitcoin-dev at lists.linuxfoundation.org>
> Subject: Re: [bitcoin-dev] Dynamically Controlled Bitcoin Block Size
>         Max Cap
> Message-ID:
>         <CADJgMzvV7cSW9aBnAf5zX7FDxN5E=AW=rET2i9EnysLao=
> vVyw at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
> On Mon, Aug 17, 2015 at 10:59 AM, Patrick Strateman via bitcoin-dev <
> bitcoin-dev at lists.linuxfoundation.org> wrote:
> > Nobody is going to click that...
> I guess I am nobody. Here's a copy of the text:-
> *Dynamically Controlled Bitcoin Block Size Max Cap
> <http://upalc.com/maxblocksize.php>*
> *Assumption*: This article is for those, who already understand the bitcoin
> protocol and aware of the block size controversy. Details of the problem
> statement can be found in BIP 100
> <http://gtf.org/garzik/bitcoin/BIP100-blocksizechangeproposal.pdf>.
> Satoshi's opinion regarding block size can be found here
> <https://bitcointalk.org/index.php?topic=1347.msg15366#msg15366>. I will
> be
> directly going into the solution without explaining the problem in details.
> *Solution*: Difficulty changes at every 2016 block, i.e. at every 2016
> block each full node does a calculation to find the next target. We will do
> just another calculation here. Nodes will also calculate what % of blocks
> in the last difficulty period is higher than 90% of the maximum block size,
> which is 1 MB for now. If it is found that more than 90% blocks in the last
> difficulty period is higher than 90% of the maximum block size, then double
> the maximum block size. If not, then calculate what % of blocks in the last
> difficulty period is less than 50% of the maximum block size. If it is
> higher than 90%, then half the maximum block size. If none of the above
> condition satisfies, keep the maximum block size as it is.
> Please note that, while calculating the % of blocks, it is better to take
> into account the first 2000 of the 2016, than the whole of 2016. This helps
> to avoid the calculation mistake if some of the last few blocks get
> orphaned.
> *Reasoning*: This solution is derived directly from the indication of the
> problem. If transaction volume increases, then we will naturally see bigger
> blocks. On the contrary, if there are not enough transaction volume, but
> maximum block size is high, then only few blocks may sweep the mempool.
> Hence, if block size is itself taken into consideration, then maximum block
> size can most rationally be derived. Moreover, this solution not only
> increases, but also decreases the maximum block size, just like difficulty.
> *Other Solutions of this Problem*:-
> Making Decentralized Economic Policy
> <http://gtf.org/garzik/bitcoin/BIP100-blocksizechangeproposal.pdf> - by
> Jeff Garzik
> Elastic block cap with rollover penalties
> <https://bitcointalk.org/index.php?topic=1078521> ? by Meni Rosenfeld
> Increase maximum block size
> <https://github.com/bitcoin/bips/blob/master/bip-0101.mediawiki> - by
> Gavin
> Andresen
> Block size following technological growth
> <https://gist.github.com/sipa/c65665fc360ca7a176a6> - by Pieter Wuille
> The Bitcoin Lightning Network: Scalable Off-Chain Instant Payments
> <https://lightning.network/lightning-network-paper.pdf> - by Joseph Poon &
> Thaddeus Dryja
> Please share your opinion regarding this solution below. For mail
> communication, feel free to write me at bitcoin [at] upalc.com.
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