The Imaginary Block Size Debate

Bitcoin’s block size debate is not a debate. Everyone agrees on the need for a size increase.

The Bitcoin developers set a scalability target of 4000 transactions per second, approximately Visa’s daily peak rate. The question is how to get there.

Three of the five core developers have published contending Bitcoin Improvement Proposals (BIPs).

  • BIP 100 (by Jeff Garzik) removes the current block size limit and allows miners to vote on size upgrades every 3 months, with a hard limit of 32 MB.
  • BIP 101 (aka Bitcoin XT, by Gavin Andresen) increases the size limit to 8 MB and doubles it every 2 years until 2036, when it reaches 8,192 MB (8 GB).
  • BIP 103 (by Peter Wuille, co-founder of Blockstream) increases the block size by 17.7% every year until 2063.

They are all fine proposals. They are all based on gratuitous assumptions about the long-term growth prospects of CPU power, storage, and Internet bandwidth.

Next decade’s technology is an unknown variable. Fine, the developers fill the blanks with guesses. But guesses are merely expressions of prejudice.

Whether we’re arguing a block size increase of 2 MB or 8 MB or how soon, who cares? It’s software! No decision is irreversible!

The important thing is if there’s a decision at all.

On Monday, Bitcoin industry leaders signed a statement supporting BIP 101:

We have found Gavin’s arguments on both the need for larger blocks and the feasibility of their implementation to be convincing.

Wow, what an endorsement. The corporations need consensus, their business depends on it. The block size debate is a Keynesian beauty contest, and industry leaders are backing the loudest candidate.

But they should have checked with the miners.

The largest miners had been casting votes for BIP 100 long before the Bitcoin XT announcement. BIP 100 grants them the most control, but they really just want consensus too.

Keep it up. If the deadlock continues, Bitcoin users will lose trust in the system and leave. And then there will be no transaction target to worry about at all.

The miners vote using an open field in the block headers.
Left: Blocks mined in the last 24 hours.
Right: Blocks mined in the last week.
“Default” is more of an abstention than a vote for the status quo. A lot of miners are voting specifically for 8MB, which was the topic of an earlier debate.

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