Great Consensus Cleanup Revival

[MattCorallo]

@ajtowns

Requiring the presence of a commitment doesn’t prevent it from taking any particular value; so it should remain equally useful.

Huh? If we fix the coinbase witness value to 00000000height, then you cannot start shoving further commitments in it? We could go ahead and make it a merkle tree of commitments where the left-most commitment is required to be 000000height, of course, but that isn’t what I saw proposed here.

@ajtowns

Changing the coinbase witness from all zeroes would also change the witness commitment for empty blocks from the constant above, of course.

Sure, I was referring specifically to the coinbase witness value, which AFAIU currently has no consensus rules (and is only 0s by default behavior of Bitcoin Core).

@ajtowns

I don’t think that’s actually possible in a soft-fork friendly way: once you add one commitment widely deployed, adding a second commitment will either prevent those nodes from validating the commitment they could validate (making the second commitment a hard fork, or allowing miners to disable validation of the first commitment on a per-block basis by inventing their own additional commitments), or will require providing a full merkle-path to all but the most recent commitment, which effectively just means publishing all the leaf commitments in each block directly.

Indeed, any time you add a new commitment you’ll have to have new nodes give old nodes the contents of the commitments/merkle paths, but that isn’t a soft-fork-incompatible change, rather requires only a P2P extension.

@ajtowns

Having a new rule not have any effect until decades in the future seems like a good way to have people not implement it (at all, let alone correctly), and leave it to being a potentially big problem for a future generation, a la Y2K. For a simple change like this, a couple of years’ notice seems much better than ~20 years to me. (For a larger change, perhaps up to five years could be reasonable, or perhaps some similar timespan that matched mining equipment’s expected lifecycle).

Strongly agree. Also because I’d like to actually write software that is able to more easily look at block heights without looking at stupid scripts in my lifetime