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

[Nathan Wilcox <nathan@leastauthority.com>]

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On Thu, Jun 11, 2015 at 12:55 PM, Aaron Voisine <voisine@gmail.com> wrote:

> > 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.
>
>
Excellent point and alternative proposal. You're right: to get the specifi
fees, you'd need all transactions in a block, and all TxOuts with
membership proofs. Your alternative seems like a much leaner trade-off for
similar data.


>
> 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
>>
>
>


-- 
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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