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Date: Sun, 30 Oct 2022 11:02:43 +1000
From: Anthony Towns <aj@erisian.com.au>
To: "David A. Harding" <dave@dtrt.org>,
Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] On mempool policy consistency
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On Fri, Oct 28, 2022 at 09:45:09PM -1000, David A. Harding via bitcoin-dev wrote:
> I think this might be understating the problem. A 95% chance of having
> an outbound peer accept your tx conversely implies 1 in 20 payments will
> fail to propagate on their initial broadcast.
Whether that's terrible or not depends on how easy it is to retry (and how
likely the retry is to succeed) after a failure -- if a TCP packet fails,
it just gets automatically resent, and if that succeeds, there's a little
lag, but your connection is still usable. I think it's *conceivable* that
a 5% failure rate could be detectable and automatically rectified. Not
that I have a good idea how you'd actually do that, in a way that's
efficient/private/decentralised...
> Some napkin math: there are about 250,000 transactions a day; if
> we round that up to 100 million a year and assume we only want one
> transaction per year to fail to initially propagate on a network where
> 30% of nodes have adopted a more permissive policy, lightweight clients
> will need to connect to over 50 randomly selected nodes.[1]
A target failure probability of 1-in-1e8 means:
* with 8 connections, you need 90% of the network to support your txs
* with 12 connections, you need ~79%
* with 24 connections (eg everyone running a long-lived node is
listening, so long lived nodes make 12 outbound and receive about
~12 inbound; shortlived nodes just do 24 outbound), you need ~54%
So with that success target, and no preferential peering, you need
a majority of listening nodes to support your tx's features in most
reasonable scenarios, I think.
> For a more
> permissive policy only adopted by 10% of nodes, the lightweight client
> needs to connect to almost 150 nodes.
I get 175 connections needed for that scenario; or 153 with a target
failure rate of 1-in-10-million.
Cheers,
aj
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