Hi y'all, Thanks for all the comments so far!
I've pushed a series of updates to the text of the BIP repo linked in the OP. The fixes include: typos, components of the specification which were incorrect (N is the total number of items, NOT the number of txns in the block), and a few sections have been clarified. The latest version also includes a set of test vectors (as CSV files), which for a series of fp rates (1/2 to 1/2^32) includes (for 6 testnet blocks, one of which generates a "null" filter): * The block height * The block hash * The raw block itself * The previous basic+extended filter header * The basic+extended filter header for the block * The basic+extended filter for the block The size of the test vectors was too large to include in-line within the document, so we put them temporarily in a distinct folder [1]. The code used to generate the test vectors has also been included. -- Laolu [1]: https://github.com/Roasbeef/bips/tree/master/gcs_light_client On Thu, Jun 1, 2017 at 9:49 PM Olaoluwa Osuntokun <laol...@gmail.com> wrote: > > 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 > > > > Oops, realized I made a mistake. These are the stats for Feb 2016 until > about a > month ago (since height 400k iirc). > > -- Laolu > > > On Thu, Jun 1, 2017 at 12:01 PM Olaoluwa Osuntokun <laol...@gmail.com> > 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 <(385)%20886-3413> >> * 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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