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From: Riccardo Casatta <riccardo.casatta@gmail.com>
Date: Fri, 30 Mar 2018 10:06:24 +0200
Message-ID: <CADabwBDiT2zNPHZ2=OyvCVrSY3Km2oyTnhRCHyMNsjW2vLMmOg@mail.gmail.com>
To: Anthony Towns <aj@erisian.com.au>
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Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Optimized Header Sync
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Yes, I think the checkpoints and the compressed headers streams should be
handled in chunks of 2016 headers and queried by chunk number instead of
height, falling back to current method if the chunk is not full yet.

This is cache friendly and allows to avoid bit 0 and bit 1 in the bitfield
(because they are always 1 after the first header in the chunk of 2016).

2018-03-30 8:14 GMT+02:00 Anthony Towns <aj@erisian.com.au>:

> On Thu, Mar 29, 2018 at 05:50:30PM -0700, Jim Posen via bitcoin-dev wrote:
> > Taken a step further though, I'm really interested in treating the
> checkpoints
> > as commitments to chain work [...]
>
> In that case, shouldn't the checkpoints just be every 2016 blocks and
> include the corresponding bits value for that set of blocks?
>
> That way every node commits to (approximately) how much work their entire
> chain has by sending something like 10kB of data (currently), and you
> could verify the deltas in each node's chain's target by downloading the
> 2016 headers between those checkpoints (~80kB with the proposed compact
> encoding?) and checking the timestamps and proof of work match both the
> old target and the new target from adjacent checkpoints.
>
> (That probably still works fine even if there's a hardfork that allows
> difficulty to adjust more frequently: a bits value at block n*2016 will
> still enforce *some* lower limit on how much work blocks n*2016+{1..2016}
> will have to contribute; so will still allow you to estimate how much work
> will have been done, it may just be less precise than the estimate you
> could
> generate now)
>
> Cheers,
> aj
>
>


-- 
Riccardo Casatta - @RCasatta <https://twitter.com/RCasatta>

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<div dir=3D"ltr"><div>Yes, I think the checkpoints and the compressed heade=
rs streams should be handled in chunks of 2016 headers and queried by chunk=
 number instead of height, falling back to current method if the chunk is n=
ot full yet.</div><div class=3D"gmail_extra"><br></div><div class=3D"gmail_=
extra">This is cache friendly and allows to avoid bit 0 and bit 1 in the bi=
tfield (because they are always 1 after the first header in the chunk of 20=
16).</div><div class=3D"gmail_extra"><br></div><div class=3D"gmail_extra"><=
div class=3D"gmail_quote">2018-03-30 8:14 GMT+02:00 Anthony Towns <span dir=
=3D"ltr">&lt;<a href=3D"mailto:aj@erisian.com.au" target=3D"_blank">aj@eris=
ian.com.au</a>&gt;</span>:<br><blockquote class=3D"gmail_quote" style=3D"ma=
rgin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class=3D=
"">On Thu, Mar 29, 2018 at 05:50:30PM -0700, Jim Posen via bitcoin-dev wrot=
e:<br>
&gt; Taken a step further though, I&#39;m really interested in treating the=
 checkpoints<br>
</span>&gt; as commitments to chain work [...]<br>
<br>
In that case, shouldn&#39;t the checkpoints just be every 2016 blocks and<b=
r>
include the corresponding bits value for that set of blocks?<br>
<br>
That way every node commits to (approximately) how much work their entire<b=
r>
chain has by sending something like 10kB of data (currently), and you<br>
could verify the deltas in each node&#39;s chain&#39;s target by downloadin=
g the<br>
2016 headers between those checkpoints (~80kB with the proposed compact<br>
encoding?) and checking the timestamps and proof of work match both the<br>
old target and the new target from adjacent checkpoints.<br>
<br>
(That probably still works fine even if there&#39;s a hardfork that allows<=
br>
difficulty to adjust more frequently: a bits value at block n*2016 will<br>
still enforce *some* lower limit on how much work blocks n*2016+{1..2016}<b=
r>
will have to contribute; so will still allow you to estimate how much work<=
br>
will have been done, it may just be less precise than the estimate you coul=
d<br>
generate now)<br>
<br>
Cheers,<br>
aj<br>
<br>
</blockquote></div><br><br clear=3D"all"><div><br></div>-- <br><div class=
=3D"gmail_signature" data-smartmail=3D"gmail_signature"><div dir=3D"ltr">Ri=
ccardo Casatta - <a href=3D"https://twitter.com/RCasatta" target=3D"_blank"=
>@RCasatta</a></div></div>
</div></div>

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