Hi Mahadev, Thanks again for your insight.
I will no doubt be in touch to let you know how this works out. regards, Martin On 7 March 2010 23:00, Mahadev Konar <maha...@yahoo-inc.com> wrote: > Martin, > 2Mb link might certainly be a problem. We can refer to these nodes as > ZooKeeper servers. Znodes is used to data elements in the ZooKeeper data > tree. > > The Zookeeper ensemble has minimal traffic which is basically health checks > between the members of the ensemble. We call one of the members as Leader > who is leading the ensemble and the others as Followers. The Leader does > periodic health checks to see if the Followers are doing fine. This is of > the order of << 1KB/sec. > > There is some traffic when the leader election within the ensemble happens. > This might be of the order of 1-2KB/sec. > > As you mentioned the reads happen locally. So, a good enough link within > the > ensemble members is important so that these followers can be up to date > with > the Leader. But again looking at your config, looks like its mostly read > only traffic. > > One more thing you should be aware of: > Lets says a ephemeral node was created and the client died, then the > clients > connected to the slow ZooKeeper server (with 2Mb/s links) would lag behind > the other clients connected to the other servers. > > As per my opinion you should do some testing since 2Mb/sec seems a little > dodgy. > > Thanks > mahadev > > On 3/7/10 2:09 PM, "Martin Waite" <waite....@googlemail.com> wrote: > > > Hi Mahadev, > > > > The inter-site links are a nuisance. We have two data-centres with 100Mb > > links which I hope would be good enough for most uses, but we need a 3rd > > site - and currently that only has 2Mb links to the other sites. This > might > > be a problem. > > > > The ensemble would have a lot of read traffic from applications asking > which > > database to connect to for each transaction - which presumably would be > > mostly handled by local zookeeper servers (do we call these "nodes" as > > opposed to znodes ?). The write traffic would be mostly changes to > > configuration (a rare event), and changes in the health of database > servers > > - also hopefully rare. I suppose the main concern is how much ambient > > zookeeper system chatter will cross the links. Are there any > measurements > > of how much traffic is used by zookeeper in maintaining the ensemble ? > > > > Another question that occurs is whether I can link sites A,B, and C in a > > ring - so that if any one site drops out, the remaining 2 continue to > talk. > > I suppose that if the zookeeper servers are all in direct contact with > each > > other, this issue does not exist. > > > > regards, > > Martin > > > > On 7 March 2010 21:43, Mahadev Konar <maha...@yahoo-inc.com> wrote: > > > >> Hi Martin, > >> As Ted rightly mentions that ZooKeeper usually is run within a colo > >> because > >> of the low latency requirements of applications that it supports. > >> > >> Its definitely reasnoble to use it in a multi data center environments > but > >> you should realize the implications of it. The high latency/low > throughput > >> means that you should make minimal use of such a ZooKeeper ensemble. > >> > >> Also, there are things like the tick Time, the syncLimit and others > (setup > >> parameters for ZooKeeper in config) which you will need to tune a little > to > >> get ZooKeeper running without many hiccups in this environment. > >> > >> Thanks > >> mahadev > >> > >> > >> On 3/6/10 10:29 AM, "Ted Dunning" <ted.dunn...@gmail.com> wrote: > >> > >>> What you describe is relatively reasonable, even though Zookeeper is > not > >>> normally distributed across multiple data centers with all members > >> getting > >>> full votes. If you account for the limited throughput that this will > >> impose > >>> on your applications that use ZK, then I think that this can work well. > >>> Probably, you would have local ZK clusters for higher transaction rate > >>> applications. > >>> > >>> You should also consider very carefully whether having multiple data > >> centers > >>> increases or decreases your overall reliability. Unless you design > very > >>> carefully, this will normally substantially degrade reliability. > Making > >>> sure that it increases reliability is a really big task that involves a > >> lot > >>> of surprising (it was to me) considerations and considerable hardware > and > >>> time investments. > >>> > >>> Good luck! > >>> > >>> On Sat, Mar 6, 2010 at 1:50 AM, Martin Waite <waite....@googlemail.com > >>> wrote: > >>> > >>>> Is this a viable approach, or am I taking Zookeeper out of its > >> application > >>>> domain and just asking for trouble ? > >>>> > >>> > >>> > >> > >> > >
