From: Andrew Poelstra <apoelstra@wpsoftware•net>
To: Tom Zander <tomz@freedommail•ch>
Cc: bitcoin-dev@lists•linuxfoundation.org
Subject: Re: [bitcoin-dev] Small Nodes: A Better Alternative to Pruned Nodes
Date: Thu, 20 Apr 2017 20:32:12 +0000 [thread overview]
Message-ID: <20170420203211.GR10783@boulet.lan> (raw)
In-Reply-To: <2652067.QRUcnb74ny@strawberry>
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On Thu, Apr 20, 2017 at 11:46:33AM +0200, Tom Zander via bitcoin-dev wrote:
> On Wednesday, 19 April 2017 19:30:30 CEST David Vorick via bitcoin-dev
> wrote:
> > > I suggested something similar which is a much simpler version;
> > > https://zander.github.io/scaling/Pruning/
>
> > Your proposal has a significant disadvantage: If every peer is dropping
> > 75% of all blocks randomly, then you need to connect to a large number of
> > peers to download the whole blockchain.
> ...
> > If you are downloading 450,000 blocks, you will need to
> > connect to an expected 46 peers to download the whole blockchain.
>
> I don’t really see the problem here, even if your math is a off. (Statistics
> is difficult, I know). Connecting to many nodes to download faster is really
> not an issue and already happens.
>
I think the expected number of peers is actually ~47.75, which is pretty
close to David's estimate, which was wrong in a way that was actually
more favorable to the "everyone stores random blocks" scheme than the
truth.
Even assuming no archival nodes, and all nodes storing only one random
index between 5 and 255 inclusive, the chance of five arbitrary nodes
giving unique indices by chance is about 98.4%. To get the same probability
from a scheme where each peer has only 25% of the blocks, you need to
connect to 59.59 nodes.
This is over a ten-times increase in the number of nodes required to
download the entire chain, and requires participating nodes to use 25%
more space than David's proposal.
> > Your proposal is also a lot less able to handle active adversaries: if
> > nodes are randomly dropping blocks, the probability that one block in
> > particular is dropped by everyone goes up significantly.
>
> You make the assumption that this new mode of pruning will be used by 100%
> of the network, this is not how distributed systems work.
>
Storing random but complete blocks requires the assumption this is _not_ the
case; David's does not make any assumptions. So on top of the performance
considerations there is this potential DoS vector.
--
Andrew Poelstra
Mathematics Department, Blockstream
Email: apoelstra at wpsoftware.net
Web: https://www.wpsoftware.net/andrew
"A goose alone, I suppose, can know the loneliness of geese
who can never find their peace,
whether north or south or west or east"
--Joanna Newsom
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next prev parent reply other threads:[~2017-04-20 20:38 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-17 6:54 David Vorick
2017-04-17 7:11 ` Danny Thorpe
2017-04-17 7:27 ` David Vorick
2017-04-20 15:50 ` Erik Aronesty
2017-04-20 23:42 ` Aymeric Vitte
2017-04-21 13:35 ` David Kaufman
2017-04-21 15:58 ` Leandro Coutinho
2017-04-17 10:14 ` Aymeric Vitte
2017-04-19 17:30 ` David Vorick
2017-04-20 9:46 ` Tom Zander
2017-04-20 20:32 ` Andrew Poelstra [this message]
2017-04-21 8:27 ` Tom Zander
2017-04-20 11:27 ` Aymeric Vitte
2017-04-18 7:43 ` Jonas Schnelli
2017-04-18 10:50 ` Tom Zander
2017-04-18 13:07 ` Tier Nolan
2017-04-18 23:19 ` Aymeric Vitte
2017-04-19 4:28 ` udevNull
2017-04-19 13:47 ` Angel Leon
2017-04-21 20:38 ` Gregory Maxwell
2017-04-23 16:27 ` Aymeric Vitte
2017-05-03 14:03 ` Erik Aronesty
2017-05-03 19:10 ` Natanael
2017-05-03 22:45 ` Aymeric Vitte
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