I've had a busy few weeks - gearing up to launch our product at work. We should organize another hangout sometime.
-J On Sat, Jul 13, 2013 at 7:24 AM, John Blossom - Shore Communications Inc. <jblos...@shore.com> wrote: > Soo...how is this initiative going? How may I help to move it forward? > > Best Regards, > > John Blossom > President > Shore Communications Inc. > > where content, technology and people meet. (Salesmark of Shore > Communications Inc.) > > web: shore.com > blog: contentblogger.com > email: jblos...@shore.com > phone: 203.293.8511 > fax: 203.663.8259 > twitter: jblossom <https://twitter.com/jblossom> > google+: google.com/+JohnBlossom > LinkedIn: John Blossom <http://www.linkedin.com/in/johnblossom> > facebook: John Blossom > skype: jblossom > > > > On Mon, Jul 8, 2013 at 9:43 AM, John Blossom <jblos...@gmail.com> wrote: > >> Ingenious, Torben, certainly adds efficiency. John >> >> On Mon, Jul 1, 2013 at 4:38 AM, Torben Weis <torben.w...@gmail.com> wrote: >> >>> 2013/6/25 Joseph Gentle <jose...@gmail.com> >>> >>> > >>> > >> When peers connect, they send each other missing ops. Figuring out >>> > >> which ops are missing can be surprisingly tricky - but we'll figure >>> > >> that out later. New ops must be ingested in order, so we always >>> ingest >>> > >> an operation after ingesting all of its parents. >>> > >>> > Just use a Merkle Tree that is at the same time a prefix tree with >>> respect >>> to the hashes of the ops (explanation below). >>> The bandwidth usage is O(1) if both clients are in sync and O(log n) if >>> they have one or few different ops and O(n) in the worst case, where n in >>> the number of ops. >>> >>> Constructing the tree is simple. >>> Let the hash function output 20 bytes and let's encode this in hex. This >>> results in a hash-string of 40 hex-characters for each operation. >>> Each node hashes over the hashes of its children. Leaf-nodes correspond to >>> operations and thus use the hash value of their respective operation. >>> The tree-invariant is that all siblings on level x share the same prefix >>> of >>> x hex-characters. >>> The tree is not sent over the network. Instead, clients start comparing >>> the >>> hashes at the root. >>> >>> Two clients compare their root hash. If it is equal, the entire tree is >>> equal and therefore they are in sync. >>> If not, they download all direct children and repeat the procedure for >>> each >>> sub-tree rooted by one of these children. >>> For example, if child number 3 has a different hash, but all others share >>> the same hash, then we have learned that there are one or more ops with a >>> hash of 3xxxx... that are different and need syncing. >>> >>> Typically we can limit the depth of the tree to few levels. 8 levels >>> already yield a tree that could store 16^8 possible ops. So in the worst >>> case two clients need to wait for 8 round-trips to determine a missing op. >>> >>> In addition, each client sends a time stamp. So when syncing we report the >>> last time stamp received from this client and ask for all ops this client >>> received later. If these are few, then simply get them (even if we know >>> some of the ops already, because we got them from another client). If >>> there >>> are too many ops, fall back to the merkle tree. With a good approximation >>> of RTT and bandwidth, it is easy to calculate which algorithm is the best >>> to sync two clients. >>> >>> Greetings >>> Torben >>> >> >>
