Hi Joe, Thanks for the details it is more clear for me now !
Kind regards. Abdelkarim. Le jeu. 28 juin 2018 08:29, Joseph Lynch <joe.e.ly...@gmail.com> a écrit : > Hi Abdelkarim, > > Other people on this list are much more knowledgeable than me and can > correct me if I'm wrong, but my understanding is that the combination of > generation and version (aka heartbeat) form a logical clock tuple > consisting of (generation, version) and that combination is the > HeartBeatState. > > The generation is the really important part and roughly corresponds to the > last start time of that particular Cassandra process in seconds since epoch > plus any forced increments due to e.g. the gossiper stopping or starting > (nodetool disable/enable gossip). The generation is further stored on disk > in the system.local table so that during a crash or restart, even if the > system's clock moves backwards, the Cassandra node's generation should > never move backwards. Whenever a node's generation number changes it's > considered a major gossip state update by other nodes because they have to > do things like ensure they are speaking the right protocol version, compare > schema, etc ... in addition to all the versioned state changes seen below. > > The version is a counter used to show the passage of time within a > generation and is used to signal versioned gossip state changes. It starts > at zero on process start and increases by one roughly every second. There > are various pieces of metadata like a node's status, schema, rack, dc, host > id, tokens, etc... which are all versioned using this version counter when > they change (whatever shows up in nodetool gossipinfo is a good example of > these states). When the gossiper is enabled, every second, each node > increments > their local version by one, picks another peer to gossip with, and sends > out their map of versioned items to that peer; other nodes know to pick up > any new data if the version has increased. Since nodes are all gossiping > with each other, any update to one node's versioned data get's propagated > out quickly even if that node may not have directly gossiped with everyone. > Naturally, the version number only increases for a given generation, but if > the generation changes the version moves backwards (resets to zero). > > So yea, think of (generation, version) as forming a logical clock which > roughly corresponds to (~last process start in seconds since the epoch, > ~seconds since last process start) for each node. This logical clock is > used to create ordering in gossip state changes. > > Hope that was helpful, > -Joey Lynch > > On Tue, Jun 26, 2018 at 3:09 PM Abdelkrim Fitouri <abdou....@gmail.com> > wrote: > > > Hello, > > > > I am studying the gossip part on casssandra and wondering about the > > difference between the heartbeat and generation data exchanged for the > > autodiscovery. > > > > many thanks for any help. > > > > -- > > > > Best Regards. > > > > Abdelkarim. > > >
