[bitcoin-dev] Block size following technological growth

Elliot Olds elliot.olds at gmail.com
Wed Aug 5 07:29:50 UTC 2015

On Tue, Aug 4, 2015 at 4:59 AM, Jorge Timón <
bitcoin-dev at lists.linuxfoundation.org> wrote:
> Also I don't think "hitting the limit" must be necessarily harmful and
> if it is, I don't understand why hitting it at 1MB will be more
> harmful than hitting it at 2MB, 8MB or 8GB.

I don't think merely hitting the limit is bad. The level of tx fees in
equilibrium give some clue as to the level of harm being done. If fees are
at $5/tx at 1MB, it's about as bad as if fees are at $5/tx at 4MB.

There is NO criterion based on mining centralization to decide between
> 2 sizes in favor of the small one.
> It seems like the rationale it's always "the bigger the better" and
> the only limitation is what a few people concerned with mining
> centralization (while they still have time to discuss this) are
> willing to accept. If that's the case, then there won't be effectively
> any limit in the long term and Bitcoin will probably fail in its
> decentralization goals.
> I think its the proponents of a blocksize change who should propose
> such a criterion and now they have the tools to simulate different
> block sizes.

In the absence of harder data, it might be interesting to use these
simulations to graph centralization pressure as a function of bandwidth
cost over time (or other historical variables that affect centralization).
For instance, look at how high centralization pressure was in 2009
according to the simulations, given how cheap/available bandwidth was then,
compared to 2010, 2011, etc. Then we could figure out: given today's
bandwidth situation, what size blocks right now would give us the same
centralization pressure that we had in 2011, 2012, 2013, etc?

Of course this doesn't mean we should blindly assume that the level of
centralization pressure in 2012 was acceptable, and therefore any block
size increase that results in the same amount of pressure now should be
acceptable. But it might lead to a more productive discussion.

> I want us to simulate many blocksizes before rushing into a decision
> (specially because I disagree that taking a decision there is urgent
> in the first place).

IMO it is not urgent if the core devs are committed to reacting to a huge
spike in tx fees with a modest block size increase in a relatively short
time frame, if they judge the centralization risks of that increase to be
small. Greg Maxwell posted on reddit a while back something to the effect
of "the big block advocates are overstating the urgency of the block size
increase, because if there was actually a situation that required us to
increase block size, we could make the increase when it was actually
needed." I found that somewhat persuasive, but I am concerned that I
haven't seen any discussion of what the "let's wait for now" camp would
consider a valid reason to increase block size in the short term, and how
they'd make the tradeoff with tx fees or whatever else was necessitating
the increase.

Jorge, if a fee equilibrium developed at 1MB of $5/tx, and you somehow knew
with certainty that increasing to 4MB would result in a 20 cent/tx
equilibrium that would last for a year (otherwise fees would stay around $5
for that year), would you be in favor of an increase to 4MB?

For those familiar with the distinction between near/far mode thinking
popularized by Robin Hanson: focusing on concrete examples like this
encourages problem solving and consensus, and focusing on abstract
principles (like decentralization vs. usability in general) leads to people
toward using argument to signal their alliances and reduce the status of
their opponents. I think it'd be very helpful if more 1MB advocates
described what exactly would make them say "OK, in this situation a block
size increase is needed, we should do one quickly!", and also if
Gavin/Mike/Jeff described what hypothetical scenarios and/or test results
would make them want to stick with 1MB blocks for now.
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