Because one message per second is dwarfed by user request traffic even with 1000s of nodes. (vnodes may make this a bigger concern down the road.)
On Tue, Nov 27, 2012 at 6:14 PM, Isaac Huang <he.hu...@intel.com> wrote: > Hi list, > > I've been looking at the Cassandra implementation of the gossip > protocol, and it appeared to me that the size of each > GossipDigestSynMessage would grow linearly with the size of the > system: > > makeRandomGossipDigest(): > ...... > List<InetAddress> endpoints = new > ArrayList<InetAddress>(endpointStateMap.keySet()); > Collections.shuffle(endpoints, random); > > So if there's N servers participating in the gossip protocol, at each > cycle, there's totally N GossipDigestSynMessage's, each of a size linear > to N - the aggregate protocol overhead would be O(N**2). > > I'm totally new to both Cassandra and Java, so this understanding > could be very wrong. But if it's true, why hasn't it been a scalability > concern? Is it because Cassandra servers are often geographically > distributed so the protocol overhead doesn't hit a single site? Or > does Cassandra servers gossip in a hierarchy of groups that I failed > to see? > > Also, what purpose does the Collections.shuffle() serve? > > Thanks and please kindly CC me on replies. > > - Isaac -- Jonathan Ellis Project Chair, Apache Cassandra co-founder, http://www.datastax.com @spyced
