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Cc: Bitcoin Development <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Proposed alternatives to the 20MB step
function
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Tier Nolan <tier.nolan@gmail.com> writes:
> On Sat, May 16, 2015 at 1:22 AM, Rusty Russell <rusty@rustcorp.com.au>
> wrote:
>> 3) ... or maybe not, if any consumed UTXO was generated before the soft
>> fork (reducing Tier's perverse incentive).
>
> The incentive problem can be fixed by excluding UTXOs from blocks before a
> certain count.
>
> UTXOs in blocks before 375000 don't count.
OK. Be nice if these were cleaned up, but I guess it's a sunk cost.
>> 4) How do we measure UTXO size? There are some constant-ish things in
>> there (eg. txid as key, height, outnum, amount). Maybe just add 32
>> to scriptlen?
>>
>
> They can be stored as a fixed digest. That can be any size, depending on
> security requirements.
>
> Gmaxwell's cost proposal is 3-4 bytes per UTXO change. It isn't
> 4*UXTO.size - 3*UTXO.size
He said "utxo_created_size" not "utxo_created" so I assumed scriptlen?
> It is only a small nudge. With only 10% of the block space to play with it
> can't be massive.
But you made that number up? The soft cap and hard byte limit are
different beasts, so there's no need for soft cost cap < hard byte
limit.
> This requires that transactions include scriptPubKey information when
> broadcasting them.
Brilliant! I completely missed that possibility...
>> 5) Add a CHECKSIG cost. Naively, since we allow 20,000 CHECKSIGs and
>> 1MB blocks, that implies a cost of 50 bytes per CHECKSIG (but counted
>> correctly, unlike now).
>>
>> This last one implies that the initial cost limit would be 2M, but in
>> practice probably somewhere in the middle.
>>
>> tx_cost = 50*num-CHECKSIG
>> + tx_bytes
>> + 4*utxo_created_size
>> - 3*utxo_consumed_size
>>
>> > A 250 byte transaction with 2 inputs and 2 outputs would have an adjusted
>> > size of 252 bytes.
>>
>> Now cost == 352.
>
> That is to large a cost for a 10% block change. It could be included in
> the block size hard fork though.
I don't think so. Again, you're mixing units.
> I think have one combined "cost" for
> transactions is good. It means much fewer spread out transaction checks.
> The code for the cost formula would be in one place.
Agreed! Unfortunately there'll always be 2, because we really do want a
hard byte limit: it's total tx bytes which brings most concerns about
centralization. But ideally it'll be so rarely hit that it can be ~
ignored (and certainly not optimized for).
Cheers,
Rusty.
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