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From: "sickpig@gmail.com" <sickpig@gmail.com>
Date: Fri, 18 Dec 2015 11:01:52 +0100
Message-ID: <CA+c4Zoxp91rpcKFqs_FJD_o1e6QzUH0Hk+jm1r9ZVsL4so_VHA@mail.gmail.com>
To: Anthony Towns <aj@erisian.com.au>
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Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Segregated Witness in the context of Scaling
	Bitcoin
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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 wrot=
e:
> > 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 alre=
ady
> > > 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?

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<div dir=3D"ltr">Anthony, <br><br><div class=3D"gmail_extra"><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.linuxfoundat=
ion.org" target=3D"_blank">bitcoin-dev@lists.linuxfoundation.org</a>&gt;</s=
pan> wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex=
;border-left:1px #ccc solid;padding-left:1ex">On Thu, Dec 17, 2015 at 04:51=
:19PM +0100, sickpig--- via bitcoin-dev wrote:<br>
<span class=3D"">&gt; On Thu, Dec 17, 2015 at 2:09 PM, Jorge Tim=C3=B3n wro=
te:<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 class=3D"">&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 class=3D""><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>many thanks for the explanation. <br><br></div><=
div class=3D"gmail_extra">so it should be fair to say that BIP 102 + SW wou=
ld 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 the interval =
we could say <br></div><div class=3D"gmail_extra">that BIP102 + SW will bri=
ng us a max block (virtual) size equal to 1MB * 2 * 1.8 =3D 3.6<br><br></di=
v><div class=3D"gmail_extra">Is it right? <br></div><div class=3D"gmail_ext=
ra"><br><br></div><div class=3D"gmail_extra"><br></div></div>

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