Quick comment before I finish reading it completely, looks like you have no way to match the input prevouts being spent, which is rather nice from a "watch for this output being spent" pov.
On June 1, 2017 3:01:14 PM EDT, Olaoluwa Osuntokun via bitcoin-dev <bitcoin-dev@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 _______________________________________________ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
