[bitcoin-dev] The need for larger blocks

Pieter Wuille pieter.wuille at gmail.com
Fri Jun 26 14:09:18 UTC 2015


Hello all,

here I'm going to try to address a part of the block size debate which has
been troubling me since the beginning: the reason why people seem to want
it.

People say that larger blocks are necessary. In the long term, I agree - in
the sense that systems that do not evolve tend to be replaced by other
systems. This evolution can come in terms of layers on top of Bitcoin's
blockchain, in terms of the technology underlying various aspects of the
blockchain itself, and also in the scale that this technology supports.

I do, however, fundamentally disagree that a fear for a change in economics
should be considered to necessitate larger blocks. If it is, and there is
consensus that we should adapt to it, then there is effectively no limit
going forward. This is similar to how Congress voting to increase the
copyright term retroactively from time to time is really no different from
having an infinite copyright term in the first place. This scares me.

Here is how Gavin summarizes the future without increasing block sizes in
PR 6341:

> 1. Transaction confirmation times for transactions with a given fee will
rise; very-low-fee transactions will fail to get confirmed at all.
> 2. Average transaction fee paid will rise
> 3. People or applications unwilling or unable to pay the rising fees will
stop submitting transactions
> 4. People and businesses will shelve plans to use Bitcoin, stunting
growth and adoption

Is it fair to summarize this as "Some use cases won't fit any more, people
will decide to no longer use the blockchain for these purposes, and the
fees will adapt."?

I think that is already happening, and will happen at any scale. I believe
demand for payments in general is nearly infinite, and only a small portion
of it will eventually fit on a block chain (independent of whether its size
is limited by consensus rules or economic or technological means).
Furthermore, systems that compete with Bitcoin in this space already offer
orders of magnitude more capacity than we can reasonably achieve with any
blockchain technology at this point.

I don't know what subset of use cases Bitcoin will cater to in the long
term. They have already changed - you see way less betting transactions
these days than a few years ago for example - and they will keep changing,
independent of what effective block sizes we end up with. I don't think we
should be afraid of this change or try to stop it.

If you look at graphs of block sizes over time (for example,
http://rusty.ozlabs.org/?p=498), it seems to me that there is very little
"organic" growth, and a lot of sudden changes (which could correspond to
changing defaults in miner software, introduction of popular
sites/services, changes in the economy). I think these can be seen as the
economy changing to full up the available space, and I believe these will
keep happening at any size effectively available.

None of this is a reason why the size can't increase. However, in my
opinion, we should do it because we believe it increases utility and
understand the risks; not because we're afraid of what might happen if we
don't hurry up. And from that point of view, it seems silly to make a huge
increase at once...

-- 
Pieter
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