Bitcoin Unlimited (BU) – Some Questions from a skeptical point of view

Very brief simplified overview of BU:

BU works by allowing nodes to specify three new parameters:

• MG (miners only) in MB – Current maximum block generation size
• EB (in MB) – Excessive block size
• AD (number of confirmations) - Acceptable depth

Miners produce blocks up to MG, however they will build on blocks of up to EB. Only after AD confirmations, will miners build on these blocks over EB in size. Nodes regard chains with blocks smaller than EB as valid, unless it has AD confirmations, in which case nodes regard this as valid.

Questions

Determining the longest chain

• The above process appears less convergent than Bitcoin’s longest valid chain rule idea. In BU Miners are said to converge, due to the “random walk model” (http://bit.ly/2fAQlf8). Has this random walk model been tested with an altcoin? Are there plans to try this new model in an altcoin before Bitcoin?

• Miners are encouraged to observe the MG, AD and EB settings in the network, and then adjust their settings to correspond to what other do, using the new “emergent consensus” methodology. This methodology seems like a “social consensus” type system. Why is this seen as robust as the existing framework? Is this likely not to scale, like existing social consensus systems and result in disputes such that the nodes diverge onto different chains? Has this been tested on an altcoin?

• What are the thoughts on a malicous miner trying to cause problems by deliberately mining a block with a specific size that is designed to split the hashrate into two, based on observing EB settings?

Wallets

• How do SPV wallets determine the chain to use, since these do not currently have AD or EB settings?

• Will SPV wallets need to upgrade before BU is used?

• If SPV wallets need to upgrade, doesn’t this remove one of the supposed advantages of hardforks, which is that SPV clients do not need to upgrade?

• Will this make running a normal wallet much more complicated? Will an ordinary SPV wallet user needs to configure and decide on complex AD and EB settings?

• Which AD and EB settings should I use to make sure I am as safe as possible?

• Will normal SPV wallet users be required to regularly monitor the the network to see how the latest emergent consensus is going, and change their AD and EB settings?

• Will SPV wallet settings be part of the emergent consensus process, or will miners be unable to view the settings of the SPV wallets?

• It is part of the BU plan that wallets will need to track the alternative chains and warm users not to accept payments until the issue is resolved. Why are people being advised to run BU before this mechanism has been rolled out?

• Many “large blockers” are opposed to RBF, as they want to protect “0-conf”, does BU undermine multiple confirmations?

­Community

• The BU articles say “Any member can propose a "Bitcoin Unlimited Improvement Proposal" (the Proposer)” (http://bit.ly/2gumf1c). Why are only members allowed to make a proposal, unlike Core where anybody can?

Submitted November 27, 2016 at 01:12PM by jonny1000 http://bit.ly/2fAMj6j