Published on: 2019-08-16T17:44:47+00:00
In a recent email exchange on the bitcoin-dev mailing list, John Newbery discussed the concept of consensus changes in Bitcoin. He stated that once a consensus change has been activated and buried by sufficient work, its height is considered to be a historic fact. However, he noted that the exact activation method becomes less important over time.Another participant in the discussion, Peter Todd, pointed out that this notion is debatable due to Bitcoin's decentralized nature. Soft-forks, such as the activation of segwit, are backwards compatible, making it difficult to measure the preferences of economically significant nodes. Todd highlighted that it remains unclear why 100% of known blocks produced after August 1st, 2017 complied with segwit rules and the BIP9 signaling protocol for segwit.The post also mentioned the example of segwit activation at height 481,824 and raised questions about whether it was due to BIP9 version bits signaling, BIP 148 User Activated Soft Fork (UASF), or a combination of both. While these methods had similar effects in enforcing segwit, the BIP 148 UASF rejected blocks that didn't signal via the BIP9 version bits.It is possible that miners were running either the BIP9 signaling Bitcoin Core release or UASF enforcing software, or even a combination of different software. The motivations behind miners producing segwit-compliant blocks are also uncertain. It could be speculated that they expected rejection from the majority of economically significant nodes or simply wanted to enforce segwit. However, as Bitcoin is a decentralized network, no authority can definitively answer these questions.Additionally, the burying of deployments, where a consensus change is activated and buried by sufficient work, offers various benefits such as simplified consensus code, improved performance, and code structure benefits. Examples of burying deployments include the implementation of 3 ISM soft forks in BIP 90 and the enforcement of P2SH and segwit scripts.A recent merge in Bitcoin Core, PR 16060, buried the CSV and segwit activation heights to 419,328 and 481,824 respectively. However, this change could potentially cause a non-backwards compatible change and result in a chainsplit between pre-0.19 nodes and 0.19 nodes if a re-org occurs below the BIP9 segwit LOCKED_IN height. Such a scenario would require redoing over 93% of the total work ever committed to Bitcoin mining.While the proposal may theoretically lead to a consensus split, it is highly unlikely. Any circumstances that would lead to such a split would raise fundamental concerns about the security assumptions of Bitcoin. More details on these considerations can be found in the 'Considerations' section of BIP 90.
Updated on: 2023-08-02T01:16:35.454181+00:00