Eric Lombrozo [ARCHIVE] on Nostr: 📅 Original date posted:2017-06-01 📝 Original message:Thanks for sending this ...

📅 Original date posted:2017-06-01
📝 Original message:Thanks for sending this proposal! I look forward to having a great
discussion around this.

- Eric

On Thursday, June 1, 2017, Olaoluwa Osuntokun via bitcoin-dev <
bitcoin-dev at lists.linuxfoundation.org> wrote:

> Hi y'all,
>
> Alex Akselrod and I would like to propose a new light client BIP for
> consideration:
> * https://github.com/Roasbeef/bips/blob/master/gcs_light_
> client.mediawiki
>
> This BIP proposal describes a concrete specification (along with a
> reference implementations[1][2][3]) for the much discussed client-side
> filtering reversal of BIP-37. The precise details are described in the
> BIP, but as a summary: we've implemented a new light-client mode that uses
> client-side filtering based off of Golomb-Rice coded sets. Full-nodes
> maintain an additional index of the chain, and serve this compact filter
> (the index) to light clients which request them. Light clients then fetch
> these filters, query the locally and _maybe_ fetch the block if a relevant
> item matches. The cool part is that blocks can be fetched from _any_
> source, once the light client deems it necessary. Our primary motivation
> for this work was enabling a light client mode for lnd[4] in order to
> support a more light-weight back end paving the way for the usage of
> Lightning on mobile phones and other devices. We've integrated neutrino
> as a back end for lnd, and will be making the updated code public very
> soon.
>
> One specific area we'd like feedback on is the parameter selection. Unlike
> BIP-37 which allows clients to dynamically tune their false positive rate,
> our proposal uses a _fixed_ false-positive. Within the document, it's
> currently specified as P = 1/2^20. We've done a bit of analysis and
> optimization attempting to optimize the following sum:
> filter_download_bandwidth + expected_block_false_positive_bandwidth. Alex
> has made a JS calculator that allows y'all to explore the affect of
> tweaking the false positive rate in addition to the following variables:
> the number of items the wallet is scanning for, the size of the blocks,
> number of blocks fetched, and the size of the filters themselves. The
> calculator calculates the expected bandwidth utilization using the CDF of
> the Geometric Distribution. The calculator can be found here:
> https://aakselrod.github.io/gcs_calc.html. Alex also has an empirical
> script he's been running on actual data, and the results seem to match up
> rather nicely.
>
> We we're excited to see that Karl Johan Alm (kallewoof) has done some
> (rather extensive!) analysis of his own, focusing on a distinct encoding
> type [5]. I haven't had the time yet to dig into his report yet, but I
> think I've read enough to extract the key difference in our encodings: his
> filters use a binomial encoding _directly_ on the filter contents, will we
> instead create a Golomb-Coded set with the contents being _hashes_ (we use
> siphash) of the filter items.
>
> Using a fixed fp=20, I have some stats detailing the total index size, as
> well as averages for both mainnet and testnet. For mainnet, using the
> filter contents as currently described in the BIP (basic + extended), the
> total size of the index comes out to 6.9GB. The break down is as follows:
>
> * total size: 6976047156
> * total avg: 14997.220622758816
> * total median: 3801
> * total max: 79155
> * regular size: 3117183743
> * regular avg: 6701.372750217131
> * regular median: 1734
> * regular max: 67533
> * extended size: 3858863413
> * extended avg: 8295.847872541684
> * extended median: 2041
> * extended max: 52508
>
> In order to consider the average+median filter sizes in a world worth
> larger blocks, I also ran the index for testnet:
>
> * total size: 2753238530
> * total avg: 5918.95736054141
> * total median: 60202
> * total max: 74983
> * regular size: 1165148878
> * regular avg: 2504.856172982827
> * regular median: 24812
> * regular max: 64554
> * extended size: 1588089652
> * extended avg: 3414.1011875585823
> * extended median: 35260
> * extended max: 41731
>
> Finally, here are the testnet stats which take into account the increase
> in the maximum filter size due to segwit's block-size increase. The max
> filter sizes are a bit larger due to some of the habitual blocks I
> created last year when testing segwit (transactions with 30k inputs, 30k
> outputs, etc).
>
> * total size: 585087597
> * total avg: 520.8839608674402
> * total median: 20
> * total max: 164598
> * regular size: 299325029
> * regular avg: 266.4790836307566
> * regular median: 13
> * regular max: 164583
> * extended size: 285762568
> * extended avg: 254.4048772366836
> * extended median: 7
> * extended max: 127631
>
> For those that are interested in the raw data, I've uploaded a CSV file
> of raw data for each block (mainnet + testnet), which can be found here:
> * mainnet: (14MB): https://www.dropbox.com/s/
> 4yk2u8dj06njbuv/mainnet-gcs-stats.csv?dl=0
> * testnet: (25MB): https://www.dropbox.com/s/
> w7dmmcbocnmjfbo/gcs-stats-testnet.csv?dl=0
>
>
> We look forward to getting feedback from all of y'all!
>
> -- Laolu
>
>
> [1]: https://github.com/lightninglabs/neutrino
> [2]: https://github.com/Roasbeef/btcd/tree/segwit-cbf
> [3]: https://github.com/Roasbeef/btcutil/tree/gcs/gcs
> [4]: https://github.com/lightningnetwork/lnd/
>
> -- Laolu
>
>
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