My understanding is that you cannot possibly violate the 1 MB block size rule without also violating the 4 MB weight rule. Regarding size alone, the only check we care about if we accept segwit is:
https://github.com/bitcoin/bitcoin/blob/master/src/validation.cpp#L2891 [size4] If that doesn't fail due to excessive non-witness data, then there's no way that https://github.com/bitcoin/bitcoin/blob/master/src/validation.cpp#L2681 [size1] would have failed before due to excessive non-witness data. If I understood it correctly when I was explained, if I remember correctly, that last check is really just an optimization or a protection against DoS invalid blocks. If the size without any witness data is bigger than 1/4 the max_weight, then the max_weight check is certain to fail as well without having to look at any witness data at that validation stage (assuming the failure is due to excessive non-witness data). I think you are not referring to the 1 mb size limit but to related one for sigops: https://github.com/bitcoin/bitcoin/blob/master/src/validation.cpp#L2704 [sigops1] whose segwit parallel is in: https://github.com/bitcoin/bitcoin/blob/master/src/validation.cpp#L1661 [sigops4] I believe the situation is similar in checking before knowing anything about the witness data just in case that's already too much. In fact, here is clearer because MAX_BLOCK_SIGOPS_COST is used for both (and WITNESS_SCALE_FACTOR is used for the optimization case). So what I would do in a hardfork after segwit activation would be to simply equal MAX_BLOCK_BASE_SIZE=MAX_BLOCK_WEIGHT/WITNESS_SCALE_FACTOR for size1, and increase MAX_BLOCK_WEIGHT and MAX_BLOCK_ SIGOPS_COST proportionally for size4 and sigops4 respectively (well, the sigops const for sigops1 as well). If I understood segwit correctly, I believe that even though it is not activated yet, you could remove both the size1 and sigops1 checks and your node would still not accept invalid blocks by pre-bip141 rules, your node would just spend more time on invalid blocks due to currently excessive size/sigops, because it would only realize at a later validation stage. Sorry for the redundancy about the validation stage. But it is not unlikely that I'm missing something. If I am wrong about this I am spreading misinformation about segwit in several channels, so I'm very interested in corrections to my statements in this mail. On Tue, May 30, 2017 at 11:24 PM, Mark Friedenbach <m...@friedenbach.org> wrote: > The 1MB classic block size is not redundant after segwit activation. > Segwit prevents the quadratic hashing problems, but only for segwit > outputs. The 1MB classic block size prevents quadratic hashing > problems from being any worse than they are today. > > Mark > > On Tue, May 30, 2017 at 6:27 AM, Jorge Timón via bitcoin-dev > <bitcoin-dev@lists.linuxfoundation.org> wrote: >> Why not simply remove the (redundant after sw activation) 1 mb size >> limit check and increasing the weight limit without changing the >> discount or having 2 limits? >> >> >> On Wed, May 24, 2017 at 1:07 AM, Erik Aronesty via bitcoin-dev >> <bitcoin-dev@lists.linuxfoundation.org> wrote: >>> Personally, I would prefer if a 2MB lock-in that uses BIP103 for the timing. >>> >>> I think up to 20% per year can be absorbed by averages in bandwidth/CPU/RAM >>> growth, of which bandwidth seems the most constraining. >>> >>> - Erik >>> >>> >>> On Tue, May 23, 2017 at 4:23 PM, Luke Dashjr via bitcoin-dev >>> <bitcoin-dev@lists.linuxfoundation.org> wrote: >>>> >>>> In light of some recent discussions, I wrote up this BIP for a real 2 MB >>>> block >>>> size hardfork following Segwit BIP148 activation. This is not part of any >>>> agreement I am party to, nor anything of that sort. Just something to >>>> throw >>>> out there as a possible (and realistic) option. >>>> >>>> Note that I cannot recommend this to be adopted, since frankly 1 MB blocks >>>> really are still too large, and this blunt-style hardfork quite risky even >>>> with consensus. But if the community wishes to adopt (by unanimous >>>> consensus) >>>> a 2 MB block size hardfork, this is probably the best way to do it right >>>> now. >>>> The only possible way to improve on this IMO would be to integrate it into >>>> MMHF/"spoonnet" style hardfork (and/or add other unrelated-to-block-size >>>> HF >>>> improvements). >>>> >>>> I have left Author blank, as I do not intend to personally champion this. >>>> Before it may be assigned a BIP number, someone else will need to step up >>>> to >>>> take on that role. Motivation and Rationale are blank because I do not >>>> personally think there is any legitimate rationale for such a hardfork at >>>> this >>>> time; if someone adopts this BIP, they should complete these sections. (I >>>> can >>>> push a git branch with the BIP text if someone wants to fork it.) >>>> >>>> <pre> >>>> BIP: ? >>>> Layer: Consensus (hard fork) >>>> Title: Post-segwit 2 MB block size hardfork >>>> Author: FIXME >>>> Comments-Summary: No comments yet. >>>> Comments-URI: ? >>>> Status: Draft >>>> Type: Standards Track >>>> Created: 2017-05-22 >>>> License: BSD-2-Clause >>>> </pre> >>>> >>>> ==Abstract== >>>> >>>> Legacy Bitcoin transactions are given the witness discount, and a block >>>> size >>>> limit of 2 MB is imposed. >>>> >>>> ==Copyright== >>>> >>>> This BIP is licensed under the BSD 2-clause license. >>>> >>>> ==Specification== >>>> >>>> Upon activation, a block size limit of 2000000 bytes is enforced. >>>> The block weight limit remains at 4000000 WU. >>>> >>>> The calculation of block weight is modified: >>>> all witness data, including both scriptSig (used by pre-segwit inputs) and >>>> segwit witness data, is measured as 1 weight-unit (WU), while all other >>>> data >>>> in the block is measured as 4 WU. >>>> >>>> The witness commitment in the generation transaction is no longer >>>> required, >>>> and instead the txid merkle root in the block header is replaced with a >>>> hash >>>> of: >>>> >>>> 1. The witness reserved value. >>>> 2. The witness merkle root hash. >>>> 3. The transaction ID merkle root hash. >>>> >>>> The maximum size of a transaction stripped of witness data is limited to 1 >>>> MB. >>>> >>>> ===Deployment=== >>>> >>>> This BIP is deployed by flag day, in the block where the median-past time >>>> surpasses 1543503872 (2018 Nov 29 at 15:04:32 UTC). >>>> >>>> It is assumed that when this flag day has been reached, Segwit has been >>>> activated via BIP141 and/or BIP148. >>>> >>>> ==Motivation== >>>> >>>> FIXME >>>> >>>> ==Rationale== >>>> >>>> FIXME >>>> >>>> ==Backwards compatibility== >>>> >>>> This is a hardfork, and as such not backward compatible. >>>> It should not be deployed without consent of the entire Bitcoin community. >>>> Activation is scheduled for 18 months from the creation date of this BIP, >>>> intended to give 6 months to establish consensus, and 12 months for >>>> deployment. >>>> >>>> ==Reference implementation== >>>> >>>> FIXME >>>> >>>> >>>> >>>> _______________________________________________ >>>> bitcoin-dev mailing list >>>> bitcoin-dev@lists.linuxfoundation.org >>>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev >>> >>> >>> >>> _______________________________________________ >>> bitcoin-dev mailing list >>> bitcoin-dev@lists.linuxfoundation.org >>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev >>> >> _______________________________________________ >> bitcoin-dev mailing list >> bitcoin-dev@lists.linuxfoundation.org >> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev _______________________________________________ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev