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From: Mark Friedenbach <mark@friedenbach.org>
Date: Sat, 19 Dec 2015 15:50:41 +0800
Message-ID: <CAOG=w-tO+QCtobd=pJe_0DTNi53svKkqMY2DMO7a8x53tT0+9w@mail.gmail.com>
To: "sickpig@gmail.com" <sickpig@gmail.com>
Content-Type: multipart/alternative; boundary=089e0115fca05bc59005273b8498
Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>,
	Anthony Towns <aj@erisian.com.au>
Subject: Re: [bitcoin-dev] Segregated Witness in the context of Scaling
	Bitcoin
Precedence: list

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Not entirely correct, no. Edge cases also matter. Segwit is described as
4MB because that is the largest possible combined block size that can be
constructed. BIP 102 + segwit would allow a maximum relay of 8MB. So you
have to be confident that an 8MB relay size would be acceptable, even if a
block full of actual transactions would be closer to 3.5MB.

On Fri, Dec 18, 2015 at 6:01 PM, sickpig--- via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> Anthony,
>
>
> On Thu, Dec 17, 2015 at 6:55 PM, Anthony Towns via bitcoin-dev <
> bitcoin-dev@lists.linuxfoundation.org> wrote:
>
>> On Thu, Dec 17, 2015 at 04:51:19PM +0100, sickpig--- via bitcoin-dev
>> wrote:
>> > On Thu, Dec 17, 2015 at 2:09 PM, Jorge Tim=C3=B3n wrote:
>> > > Unless I'm missing something, 2 mb x4 =3D 8mb, so bip102 + SW is alr=
eady
>> > > equivalent to the 2-4-8 "compromise" proposal [...]
>> > isn't SegWit gain ~75%? hence 2mb x 1.75 =3D 3.5.
>>
>> Segwit as proposed gives a 75% *discount* to witness data with the
>> same limit, so at a 1MB limit, that might give you (eg) 2.05MB made up
>> of 650kB of base block data plus 1.4MB of witness data; where 650kB +
>> 1.4MB/4 =3D 1MB at the 1MB limit; or 4.1MB made up of 1.3MB of base plus
>> 2.8MB of witness, for 1.3MB+2.8MB/4 =3D 2MB at a 2MB limit.
>>
>> > 4x is theoric gain you get in case of 2-2 multisig txs.
>>
>> With segregated witness, 2-2 multisig transactions are made up of 94B
>> of base data, plus about 214B of witness data; discounting the witness
>> data by 75% gives 94+214/4=3D148 bytes. That compares to about 301B for
>> a 2-2 multisig transaction with P2SH rather than segwit, and 301/148
>> gives about a 2.03x gain, not a 4x gain. A 2.05x gain is what I assumed
>> to get the numbers above.
>>
>> You get further improvements with, eg, 3-of-3 multisig, but to get
>> the full, theoretical 4x gain you'd need a fairly degenerate looking
>> transaction.
>>
>> Pay to public key hash with segwit lets you move about half the
>> transaction data into the witness, giving about a 1.6x improvement by
>> my count (eg 1.6MB =3D 800kB of base data plus 800kB of witness data,
>> where 800kB+800kB/4=3D1MB), so I think a gain of between 1.6 and 2.0 is
>> a reasonable expectation to have for the proposed segwit scheme overall.
>>
>>
> many thanks for the explanation.
>
> so it should be fair to say that BIP 102 + SW would bring a gain between
> 2*1.6 and 2*2.
>
> Just for the sake of simplicity if we take the middle of the interval we
> could say
> that BIP102 + SW will bring us a max block (virtual) size equal to 1MB * =
2
> * 1.8 =3D 3.6
>
> Is it right?
>
>
>
>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
>

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<div dir=3D"ltr">Not entirely correct, no. Edge cases also matter. Segwit i=
s described as 4MB because that is the largest possible combined block size=
 that can be constructed. BIP 102 + segwit would allow a maximum relay of 8=
MB. So you have to be confident that an 8MB relay size would be acceptable,=
 even if a block full of actual transactions would be closer to 3.5MB.<br><=
/div><div class=3D"gmail_extra"><br><div class=3D"gmail_quote">On Fri, Dec =
18, 2015 at 6:01 PM, sickpig--- via bitcoin-dev <span dir=3D"ltr">&lt;<a hr=
ef=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" target=3D"_blank">bitco=
in-dev@lists.linuxfoundation.org</a>&gt;</span> wrote:<br><blockquote class=
=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padd=
ing-left:1ex"><div dir=3D"ltr">Anthony, <br><br><div class=3D"gmail_extra">=
<div><div class=3D"h5"><br><div class=3D"gmail_quote">On Thu, Dec 17, 2015 =
at 6:55 PM, Anthony Towns via bitcoin-dev <span dir=3D"ltr">&lt;<a href=3D"=
mailto:bitcoin-dev@lists.linuxfoundation.org" target=3D"_blank">bitcoin-dev=
@lists.linuxfoundation.org</a>&gt;</span> wrote:<br><blockquote class=3D"gm=
ail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-le=
ft:1ex">On Thu, Dec 17, 2015 at 04:51:19PM +0100, sickpig--- via bitcoin-de=
v wrote:<br>
<span>&gt; On Thu, Dec 17, 2015 at 2:09 PM, Jorge Tim=C3=B3n wrote:<br>
&gt; &gt; Unless I&#39;m missing something, 2 mb x4 =3D 8mb, so bip102 + SW=
 is already<br>
</span>&gt; &gt; equivalent to the 2-4-8 &quot;compromise&quot; proposal [.=
..]<br>
<span>&gt; isn&#39;t SegWit gain ~75%? hence 2mb x 1.75 =3D 3.5.<br>
<br>
</span>Segwit as proposed gives a 75% *discount* to witness data with the<b=
r>
same limit, so at a 1MB limit, that might give you (eg) 2.05MB made up<br>
of 650kB of base block data plus 1.4MB of witness data; where 650kB +<br>
1.4MB/4 =3D 1MB at the 1MB limit; or 4.1MB made up of 1.3MB of base plus<br=
>
2.8MB of witness, for 1.3MB+2.8MB/4 =3D 2MB at a 2MB limit.<br>
<span><br>
&gt; 4x is theoric gain you get in case of 2-2 multisig txs.<br>
<br>
</span>With segregated witness, 2-2 multisig transactions are made up of 94=
B<br>
of base data, plus about 214B of witness data; discounting the witness<br>
data by 75% gives 94+214/4=3D148 bytes. That compares to about 301B for<br>
a 2-2 multisig transaction with P2SH rather than segwit, and 301/148<br>
gives about a 2.03x gain, not a 4x gain. A 2.05x gain is what I assumed<br>
to get the numbers above.<br>
<br>
You get further improvements with, eg, 3-of-3 multisig, but to get<br>
the full, theoretical 4x gain you&#39;d need a fairly degenerate looking<br=
>
transaction.<br>
<br>
Pay to public key hash with segwit lets you move about half the<br>
transaction data into the witness, giving about a 1.6x improvement by<br>
my count (eg 1.6MB =3D 800kB of base data plus 800kB of witness data,<br>
where 800kB+800kB/4=3D1MB), so I think a gain of between 1.6 and 2.0 is<br>
a reasonable expectation to have for the proposed segwit scheme overall.<br=
>
<br></blockquote><br></div></div></div>many thanks for the explanation. <br=
><br></div><div class=3D"gmail_extra">so it should be fair to say that BIP =
102 + SW would bring a gain between 2*1.6 and 2*2. <br></div><div class=3D"=
gmail_extra"><br>Just for the sake of simplicity if we take the middle of t=
he interval we could say <br></div><div class=3D"gmail_extra">that BIP102 +=
 SW will bring us a max block (virtual) size equal to 1MB * 2 * 1.8 =3D 3.6=
<br><br></div><div class=3D"gmail_extra">Is it right? <br></div><div class=
=3D"gmail_extra"><br><br></div><div class=3D"gmail_extra"><br></div></div>
<br>_______________________________________________<br>
bitcoin-dev mailing list<br>
<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-dev@lists.=
linuxfoundation.org</a><br>
<a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" =
rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoundation.org/mail=
man/listinfo/bitcoin-dev</a><br>
<br></blockquote></div><br></div>

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