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Date: Wed, 9 Dec 2015 01:58:06 +0100
Message-ID: <CABm2gDrb4ka_sYG-jRzg=gqWvtxLysbRxXCLYL+F5HMqDP0jGg@mail.gmail.com>
From: =?UTF-8?B?Sm9yZ2UgVGltw7Nu?= <jtimon@jtimon.cc>
To: Gregory Maxwell <greg@xiph.org>
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Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Capacity increases for the Bitcoin system.
Precedence: list

On Wed, Dec 9, 2015 at 12:59 AM, Gregory Maxwell via bitcoin-dev
<bitcoin-dev@lists.linuxfoundation.org> wrote:
> On Tue, Dec 8, 2015 at 3:12 PM, Gavin Andresen via bitcoin-dev
> <bitcoin-dev@lists.linuxfoundation.org> wrote:
> We already have consensus critical enforcement there, the height,
> which has almost never been problematic. (A popular block explorer
> recently misimplemented the var-int decode and suffered an outage).

It would be also a nice opportunity to move the height to a more
accessible place.
For example CBlockHeader::hashMerkleRoot (and CBlockIndex's) could be
replaced with a hash of the following struct:

struct hashRootStruct
{
uint256 hashMerkleRoot;
uint256 hashWitnessesRoot;
int32_t nHeight;
}

> From a risk reduction perspective, I think it is much preferable to
> perform the primary change in a backwards compatible manner, and pick
> up the data reorganization in a hardfork if anyone even cares.


But then all wallet software will need to adapt their software twice.
Why introduce technical debt for no good reason?

> I think thats generally a nice cadence to split up risks that way; and
> avoid controversy.

Uncontroversial hardforks can also be deployed with small risks as
described in BIP99.