Re: [bitcoin-dev] BIP proposal: NODE_NETWORK_LIMITED service bits

From: Eric Voskuil <eric@voskuil•org>
To: Aymeric Vitte <vitteaymeric@gmail•com>,
	Jonas Schnelli <dev@jonasschnelli•ch>,
	Luke Dashjr <luke@dashjr•org>
Cc: bitcoin-dev@lists•linuxfoundation.org
Subject: Re: [bitcoin-dev] BIP proposal: NODE_NETWORK_LIMITED service bits
Date: Thu, 11 May 2017 14:05:09 -0700	[thread overview]
Message-ID: <b1bd85b6-a2c4-6243-ff41-a514eef1c334@voskuil.org> (raw)
In-Reply-To: <f0417e14-fb2c-3572-f8e9-06c7adbf3d2b@gmail.com>

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On 05/11/2017 01:36 PM, Aymeric Vitte via bitcoin-dev wrote:
> Sorry again, is this discussion really serious?
> 
> In this thread, previous ones or others, the level of approximation
> is obvious, often shadowed by useless maths/papers and strange
> calculations that are not helping, at the end nobody knows what
> would happen "if", how far the chain can roll back, etc
> 
> Then don't make pruning the default if it's the current concern,
> pruning is of no use
> 
> Again, the priority should be to scale the full nodes

I agree. Every full node operator should (and likely would at some
point) simply never connect to, or relay the address of, any "peer"
advertising itself as diminished. Why on earth would a full node
operator want to encourage shrinking support for bootstrapping and
deep reorgs, resulting in greater load for himself. That's a race to
the bottom.

We are literally talking about $7.50 for the *entire chain* with
breathing room. If someone wants to save a few dollars they are better
off attempting to hide their pruning.

e

> Le 11/05/2017 à 22:10, Jonas Schnelli via bitcoin-dev a écrit :
>>> Is 49 days particularly useful? Would it be a problem to
>>> instead leave both- bits undefined? I'm thinking this might be
>>> better as a way to indicate "7 days, plus a deterministically
>>> chosen set of historical blocks"…
>> I though two service bits allow three states and we should define
>> all three combinations. But I guess an adequate „definition“
>> would be to reserve it for future „definitions“. Or use Gregory's
>> proposal of min 2016*2 blocks & keep it „undefined“ for now.
>> 
>> 49 days was chosen to allow SPV peers to be „offline“ for a month
>> and still be capable to catch-up with a peer pruned to a datadir
>> of ~10GB.
>> 
>>> This is technically true right now, but as soon as segwit
>>> activates, it will no longer be... Therefore, I suggest
>>> striking it from the BIP, expounding on it in greater detail,
>>> or making it true for the longer term.
>> AFAIK Core does also guaranteed the 288 blocks post segwit
>> activation: 
>> https://github.com/bitcoin/bitcoin/blob/08a7316c144f9f2516db8fa624008
93f4358c5ae/src/validation.h#L204
>>
>> 
But maybe I’m confused.
>> 
>>>> Peers following this BIP SHOULD connect a limited amount of
>>>> their available outbound connections to peers signaling one
>>>> or both of the NODE_NETWORK_LIMITED_* service bits if they
>>>> expect to request less blocks than the signaled number.
>>> This isn't entirely clear whether it refers to peers
>>> downloading blocks, or peers serving them. (I assume the
>>> former, but it should be clarified.)
>> Indeed. I’ll try to make that more clear.
>> 
>>>> Light clients (and such) who are not checking the
>>>> nServiceFlags (service bits) from a relayed addr-message may
>>>> unwillingly connect to a pruned peer and ask for (filtered)
>>>> blocks at a depth below their pruned depth.
>>> Wouldn't this already be a problem, without the BIP?
>> AFAIK, Core does currently only relay NODE_NETWORK addresses. But
>> yes, It may be a problem already.
>> 
>> </jonas>
>> 
>> 
>> 
>> _______________________________________________ bitcoin-dev
>> mailing list bitcoin-dev@lists•linuxfoundation.org 
>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
> 
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