Subject: Re: [Bitcoin-development] [Bulk] Re: Proposed additional options for pruned nodes

From: gb <[email-masked]>
Date: Wed, 13 May 2015 09:30:03 +1200

This seems like a good place to add in an idea I had about
partially-connected nodes that are able to throttle bandwidth demands.
While we will be having partial-blockchain nodes with a spectrum of
storage options the requirement to be connected is somewhat binary, I
think many users manually throttle by turning nodes on/off already with
a minimum to just keep the chain up to date. A throttling option would
leverage on bitcoin's asychronous design to reduce bandwidth demands for
weaker nodes.

So throttling to allow for a spectrum of bandwidth connectivity:

1) an option for the user -throttle=XXX that would allow the user to
specify a desirable total bandwidth XXX in Gbytes/day the bitcoin client
can use.

2) the client reduces the number of continuous connections, transaction
or block relaying to achieve the desired throttling rate

3) it could do this by being partially connected throughout the duty
cycle or cycling the node on/off for a percentage of a 24(?) hr period

4) have an auto setting where some smart traffic management 'just takes
care of it' and manual settings that can be user configured

5) reduces minimum requirement for any 24(?) hr period it has received a
full copy of all blocks to remain fully-validating

Not sure if anyone has bought such an idea forward or if there are
obvious holes, so pre-emptive apologies for time-wasting if so.

On Tue, 2015-05-12 at 15:43 -0400, gabe appleton wrote:
> Yet this holds true in our current assumptions of the network as well:
> that it will become a collection of pruned nodes with a few storage
> nodes. 
> 
> A hybrid option makes this better, because it spreads the risk, rather
> than concentrating it in full nodes. 
> 
> On May 12, 2015 3:38 PM, "Jeff Garzik" <[email-masked]> wrote:
>         One general problem is that security is weakened when an
>         attacker can DoS a small part of the chain by DoS'ing a small
>         number of nodes - yet the impact is a network-wide DoS because
>         nobody can complete a sync.
>         
>         
>         
>         On Tue, May 12, 2015 at 12:24 PM, gabe appleton
>         <[email-masked]> wrote:
>                 0, 1, 3, 4, 5, 6 can be solved by looking at chunks
>                 chronologically. Ie, give the signed (by sender) hash
>                 of the first and last block in your range. This is
>                 less data dense than the idea above, but it might work
>                 better. 
>                 
>                 That said, this is likely a less secure way to do it.
>                 To improve upon that, a node could request a block of
>                 random height within that range and verify it, but
>                 that violates point 2. And the scheme in itself
>                 definitely violates point 7.
>                 
>                 On May 12, 2015 3:07 PM, "Gregory Maxwell"
>                 <[email-masked]> wrote:
>                         It's a little frustrating to see this just
>                         repeated without even
>                         paying attention to the desirable
>                         characteristics from the prior
>                         discussions.
>                         
>                         Summarizing from memory:
>                         
>                         (0) Block coverage should have locality;
>                         historical blocks are
>                         (almost) always needed in contiguous ranges.
>                          Having random peers
>                         with totally random blocks would be horrific
>                         for performance; as you'd
>                         have to hunt down a working peer and make a
>                         connection for each block
>                         with high probability.
>                         
>                         (1) Block storage on nodes with a fraction of
>                         the history should not
>                         depend on believing random peers; because
>                         listening to peers can
>                         easily create attacks (e.g. someone could
>                         break the network; by
>                         convincing nodes to become unbalanced) and not
>                         useful-- it's not like
>                         the blockchain is substantially different for
>                         anyone; if you're to the
>                         point of needing to know coverage to fill then
>                         something is wrong.
>                         Gaps would be handled by archive nodes, so
>                         there is no reason to
>                         increase vulnerability by doing anything but
>                         behaving uniformly.
>                         
>                         (2) The decision to contact a node should need
>                         O(1) communications,
>                         not just because of the delay of chasing
>                         around just to find who has
>                         someone; but because that chasing process
>                         usually makes the process
>                         _highly_ sybil vulnerable.
>                         
>                         (3) The expression of what blocks a node has
>                         should be compact (e.g.
>                         not a dense list of blocks) so it can be
>                         rumored efficiently.
>                         
>                         (4) Figuring out what block (ranges) a peer
>                         has given should be
>                         computationally efficient.
>                         
>                         (5) The communication about what blocks a node
>                         has should be compact.
>                         
>                         (6) The coverage created by the network should
>                         be uniform, and should
>                         remain uniform as the blockchain grows;
>                         ideally it you shouldn't need
>                         to update your state to know what blocks a
>                         peer will store in the
>                         future, assuming that it doesn't change the
>                         amount of data its
>                         planning to use. (What Tier Nolan proposes
>                         sounds like it fails this
>                         point)
>                         
>                         (7) Growth of the blockchain shouldn't cause
>                         much (or any) need to
>                         refetch old blocks.
>                         
>                         I've previously proposed schemes which come
>                         close but fail one of the above.
>                         
>                         (e.g. a scheme based on reservoir sampling
>                         that gives uniform
>                         selection of contiguous ranges, communicating
>                         only 64 bits of data to
>                         know what blocks a node claims to have,
>                         remaining totally uniform as
>                         the chain grows, without any need to refetch
>                         -- but needs O(height)
>                         work to figure out what blocks a peer has from
>                         the data it
>                         communicated.;   or another scheme based on
>                         consistent hashes that has
>                         log(height) computation; but sometimes may
>                         result in a node needing to
>                         go refetch an old block range it previously
>                         didn't store-- creating
>                         re-balancing traffic.)
>                         
>                         So far something that meets all those criteria
>                         (and/or whatever ones
>                         I'm not remembering) has not been discovered;
>                         but I don't really think
>                         much time has been spent on it. I think its
>                         very likely possible.
>                         
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>         
>         
>         
>         -- 
>         Jeff Garzik
>         Bitcoin core developer and open source evangelist
>         BitPay, Inc.      https://bitpay.com/
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