[bitcoin-dev] A design for Probabilistic Partial Pruning

Leo Wandersleb leo at LeoWandersleb.de
Sun Feb 28 03:41:06 UTC 2021

Only headers need to be downloaded sequentially so downloading relevant blocks
from one node is totally possible with gaps in between.

On 2/27/21 4:10 AM, Igor Cota via bitcoin-dev wrote:
> Hi Keagan,
> I had a very similar idea. The only difference being for the node to decide on
> a range of blocks to keep beforehand, rather than making the decision
> block-by-block like you suggest.
> I felt the other nodes would be better served by ranges due to the sequential
> nature of IBD. Perhaps this would be computationally lighter as well.
> I also encourage you to read Ryosuke Abe's paper [1] that proposes a DHT
> scheme to solve this same problem.
> Cheers,
> Igor
> [1] https://arxiv.org/abs/1902.02174
> On Fri, 26 Feb 2021 at 21:57, Keagan McClelland via bitcoin-dev
> <bitcoin-dev at lists.linuxfoundation.org
> <mailto:bitcoin-dev at lists.linuxfoundation.org>> wrote:
>     Hi all,
>     I've been thinking for quite some time about the problem of pruned nodes
>     and ongoing storage costs for full nodes. One of the things that strikes
>     me as odd is that we only really have two settings.
>     A. Prune everything except the most recent blocks, down to the cache size
>     B. Keep everything since genesis
>     From my observations and conversations with various folks in the
>     community, they would like to be able to run a "partially" pruned node to
>     help bear the load of bootstrapping other nodes and helping with data
>     redundancy in the network, but would prefer to not dedicate hundreds of
>     Gigabytes of storage space to the cause.
>     This led me to the idea that a node could randomly prune some of the
>     blocks from history if it passed some predicate. A rough sketch of this
>     would look as follows.
>     1. At node startup, it would generate a random seed, this would be unique
>     to the node but not necessary that it be cryptographically secure.
>     2. In the node configuration it would also carry a "threshold" expressed
>     as some percentage of blocks it wanted to keep.
>     3. As IBD occurs, based off of the threshold, the block hash, and the
>     node's unique seed, the node would either decide to prune the data or keep
>     it. The uniqueness of the node's hash should ensure that no block is
>     systematically overrepresented in the set of nodes choosing this storage
>     scheme.
>     4. Once the node's IBD is complete it would advertise this as a peer
>     service, advertising its seed and threshold, so that nodes could
>     deterministically deduce which of its peers had which blocks.
>     The goals are to increase data redundancy in a way that more uniformly
>     shares the load across nodes, alleviating some of the pressure of full
>     archive nodes on the IBD problem. I am working on a draft BIP for this
>     proposal but figured I would submit it as a high level idea in case anyone
>     had any feedback on the initial design before I go into specification
>     levels of detail.
>     If you have thoughts on
>     A. The protocol design itself
>     B. The barriers to put this kind of functionality into Core
>     I would love to hear from you,
>     Cheers,
>     Keagan
>     _______________________________________________
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> -- 
> *Igor Cota*
> Codex Apertus d.o.o.
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