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Date: Sat, 16 May 2015 12:09:50 +0100
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From: Tier Nolan <tier.nolan@gmail.com>
Cc: Bitcoin Development <bitcoin-development@lists.sourceforge.net>
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Subject: Re: [Bitcoin-development] Proposed alternatives to the 20MB step
function
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On Sat, May 16, 2015 at 1:22 AM, Rusty Russell <rusty@rustcorp.com.au>
wrote:
> Some tweaks:
>
> 1) Nomenclature: call tx_size "tx_cost" and real_size "tx_bytes"?
>
Fair enough.
>
> 2) If we have a reasonable hard *byte* limit, I don't think that we need
> the MAX(). In fact, it's probably OK to go negative.
>
I agree, we want people to compress the UTXO space and a transaction with
100 inputs and one output is great.
It may have privacy problem though.
>
> 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.
>
> 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
It is only a small nudge. With only 10% of the block space to play with it
can't be massive.
This requires that transactions include scriptPubKey information when
broadcasting them.
>
> 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 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.
--001a11459238d86087051630ff21
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
<div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote">On S=
at, May 16, 2015 at 1:22 AM, Rusty Russell <span dir=3D"ltr"><<a href=3D=
"mailto:rusty@rustcorp.com.au" target=3D"_blank">rusty@rustcorp.com.au</a>&=
gt;</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 =
0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Some tweaks:<br>
<br>
1) Nomenclature: call tx_size "tx_cost" and real_size "tx_by=
tes"?<br></blockquote><div><br></div><div>Fair enough. <br></div><bloc=
kquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #cc=
c solid;padding-left:1ex">
<br>
2) If we have a reasonable hard *byte* limit, I don't think that we nee=
d<br>
=C2=A0 =C2=A0the MAX().=C2=A0 In fact, it's probably OK to go negative.=
<br></blockquote><div><br></div><div>I agree, we want people to compress th=
e UTXO space and a transaction with 100 inputs and one output is great.<br>=
<br></div><div>It may have privacy problem though.<br></div><div>=C2=A0</di=
v><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:=
1px #ccc solid;padding-left:1ex">
<br>
3) ... or maybe not, if any consumed UTXO was generated before the soft<br>
=C2=A0 =C2=A0fork (reducing Tier's perverse incentive).<br></blockquote=
><div><br></div><div>The incentive problem can be fixed by excluding UTXOs =
from blocks before a certain count.<br><br></div><div>UTXOs in blocks befor=
e 375000 don't count.<br></div><div>=C2=A0</div><blockquote class=3D"gm=
ail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-le=
ft:1ex">
<br>
4) How do we measure UTXO size?=C2=A0 There are some constant-ish things in=
<br>
=C2=A0 =C2=A0there (eg. txid as key, height, outnum, amount).=C2=A0 Maybe j=
ust add 32<br>
=C2=A0 =C2=A0to scriptlen?<br></blockquote><div><br></div><div>They can be =
stored as a fixed digest.=C2=A0 That can be any size, depending on security=
requirements.<br><br></div><div>Gmaxwell's cost proposal is 3-4 bytes =
per UTXO change.=C2=A0 It isn't 4*UXTO.size - 3*UTXO.size<br><br>It is =
only a small nudge.=C2=A0 With only 10% of the block space to play with it =
can't be massive.<br></div><div><br></div><div>This requires that trans=
actions include scriptPubKey information when broadcasting them.<br></div><=
div>=C2=A0</div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8e=
x;border-left:1px #ccc solid;padding-left:1ex">
<br>
5) Add a CHECKSIG cost.=C2=A0 Naively, since we allow 20,000 CHECKSIGs and<=
br>
=C2=A0 =C2=A01MB blocks, that implies a cost of 50 bytes per CHECKSIG (but =
counted<br>
=C2=A0 =C2=A0correctly, unlike now).<br>
<br>
This last one implies that the initial cost limit would be 2M, but in<br>
practice probably somewhere in the middle.<br>
<br>
=C2=A0 tx_cost =3D 50*num-CHECKSIG<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 + tx_bytes<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 + 4*utxo_created_si=
ze<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 - 3*utxo_consumed_s=
ize<br>
<span class=3D""><br>
> A 250 byte transaction with 2 inputs and 2 outputs would have an adjus=
ted<br>
> size of 252 bytes.<br>
<br>
</span>Now cost =3D=3D 352.<br></blockquote><div><br></div><div>That is to =
large a cost for a 10% block change.=C2=A0 It could be included in the bloc=
k size hard fork though.=C2=A0 I think have one combined "cost" f=
or transactions is good.=C2=A0 It means much fewer spread out transaction c=
hecks.=C2=A0 The code for the cost formula would be in one place.<br></div>=
</div></div></div>
--001a11459238d86087051630ff21--
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