Re: [Bitcoin-development] Proposal: SPV Fee Discovery mechanism

[Aaron Voisine <voisine@gmail.com>]

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> A Header-PoW-verifying client could still be given all transactions in a
recent block, from which it can see the in-band fees directly.

You don't know the fees paid by any given transaction unless you also have
all it's inputs. Transaction inputs do not include an amount. You could
however get the average fee-per-kb paid by all transactions in a block by
looking at the coinbase transaction, subtracting the block reward, and
dividing by the size of block minus the header.


Aaron Voisine
co-founder and CEO
breadwallet.com

On Thu, Jun 11, 2015 at 11:30 AM, Nathan Wilcox <nathan@leastauthority.com>
wrote:

> On Wed, Jun 10, 2015 at 2:03 PM, Peter Todd <pete@petertodd.org> wrote:
>
>> On Wed, Jun 10, 2015 at 02:00:27PM -0600, Nathan Wilcox wrote:
>> > On Wed, Jun 10, 2015 at 1:19 PM, Aaron Voisine <voisine@gmail.com>
>> wrote:
>> >
>> > > It could be done by agreeing on a data format and encoding it in an
>> > > op_return output in the coinbase transaction. If it catches on it
>> could
>> > > later be enforced with a soft fork.
>> > >
>> > >
>> > Sounds plausible, except SPV protocols would need to include this
>> coinbase
>> > txn if it's going to help SPV clients. (Until a softfork is activated,
>> SPV
>> > clients should not rely on this encoding, since until that time the
>> results
>> > can be fabricated by individual miners.)
>>
>> Fee stats can always be fabricated by individual miners because fees can
>> be paid out-of-band.
>>
>>
> This is a point I hadn't considered carefully before. I don't understand
> the marketplace here or why miners would want to move fees outside of
> explicit inband fees. Implicit in this proposal is that the statistics only
> cover in-band data, because that's the scope of consensus rules, and thus
> the proposal is only as useful as the information of in-band fees is useful.
>
> I've also noticed a detracting technical argument given a particular
> tradeoff:
>
> A Header-PoW-verifying client could still be given all transactions in a
> recent block, from which it can see the in-band fees directly.  The
> trade-off is the size of those transactions versus the need to alter any
> consensus rules or do soft forks.
>
> Notice how this trade-off's costs change with maximum block size.
>
>
>
>
>> --
>> 'peter'[:-1]@petertodd.org
>> 00000000000000001245bd2f5c99379ee76836227ded9c08324894faabc0d27f
>>
>
>
>
> --
> Nathan Wilcox
> Least Authoritarian
>
> email: nathan@leastauthority.com
> twitter: @least_nathan
> PGP: 11169993 / AAAC 5675 E3F7 514C 67ED  E9C9 3BFE 5263 1116 9993
>

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