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Date: Fri, 11 Sep 2015 13:18:10 -0400
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From: Christophe Biocca <christophe.biocca@gmail.com>
To: =?UTF-8?B?Sm9yZ2UgVGltw7Nu?= <jtimon@jtimon.cc>
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Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Bitcoin Days Destroyed as block selection
	heuristic
Precedence: list

It's pretty obvious that Dave is suggesting an alternate tie-breaker:

> It also makes an empty block far less attractive because it is easily rep=
laced, all the way until the next block locks it in.

I do see a problem with the proposal. Right now, when a miner sees a
new block with the most work and there are no ties, it is always a
good idea to build on top of it (unless they're in the middle of
building a private chain, or other pathological cases).

With this new heuristic (assuming it is actually followed by a good
chunk of people), a miner can reasonably know whether or not they can
safely mine a sibling of the block instead. When enough widely
propagated transactions exist, and the block to orphan is small,
there's minimal risk in mining a sibling block instead of a child
block (the only extra risk is in someone else mining a child block
right around the time we suceed in mining a siblish block, where we'll
definitely be orphaned instead of ~50% of the time).

Because the risk can be measured and is sometimes very small, it will
then be profitable for a miner to orphan a small non-empty block and
double-spend some confirmed transactions whenever the block confirming
them is easily replaced. This lowers the security of 1-conf
transactions.

Mind you, that risk doesn't apply if we prefer non-empty blocks to
empty blocks and leave it at that, or only switch if the new block
doesn't double spend transactions in the old one, so it's a fixable
issue.

On 11 September 2015 at 12:32, Jorge Tim=C3=B3n
<bitcoin-dev@lists.linuxfoundation.org> wrote:
>
> On Sep 11, 2015 12:27 PM, "Dave Scotese via bitcoin-dev"
> <bitcoin-dev@lists.linuxfoundation.org> wrote:
>>
>> Rather than (promising to, and when they don't actually, at least
>> pretending to) use the first-seen block, I propose that a more sophistic=
ated
>> method of choosing which of two block solutions to accept.
>
> There's already a criterion to chose: the one with more work (in valid
> blocks) on top of it.
>
>
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