For most uses, 3 instances is enough. For heavy usage, 5 instances can be used. ZooKeeper write performance degrades with the number of instances added. There's a lot of doc on the net about this.
A ZNode is a data entry in the ZooKeeper database. An instance is a server running the ZooKeeper software. -JZ On 5/8/12 3:13 PM, "Something Something" <[email protected]> wrote: >We have a cluster of 17 machines. Somewhere in the HBase documentation I >read - usually we should divide by 2 & use an odd number. May be I >mis-read. That's why I started Zookeeper on 9 machines. I guess, I don't >understand the difference between Nodes & Instance. I expected ZKNodes to >be 9. Please explain. Thanks a lot for your help. > >On Tue, May 8, 2012 at 3:05 PM, Jordan Zimmerman ><[email protected]>wrote: > >> You have 9 instances? That's a lot. Why so many? >> >> I believe the "Node" field in the stat is the number of ZKNodes, not >> instances in the ensemble. That stat looks good. It means that that >> instance is serving requests as a "follower" instance (one of the >> instances will be the leader). >> >> -JZ >> >> On 5/8/12 2:54 PM, "Something Something" <[email protected]> >>wrote: >> >> >Hmm... >> > >> > >> >Trying 127.0.0.1... >> >Connected to localhost. >> >Escape character is '^]'. >> >stat >> >Zookeeper version: 3.3.4-cdh3u3--1, built on 01/26/2012 20:09 GMT >> >Clients: >> > /127.0.0.1:42510[0](queued=0,recved=1,sent=0) >> > >> >Latency min/avg/max: 0/0/0 >> >Received: 4 >> >Sent: 3 >> >Outstanding: 0 >> >Zxid: 0x100000000 >> >Mode: follower >> >Node count: 11 >> >Connection closed by foreign host. >> > >> > >> >Not sure I understand this output. I have 9 nodes in the ensemble. >> > >> >On Tue, May 8, 2012 at 2:45 PM, Jordan Zimmerman >> ><[email protected]>wrote: >> > >> >> Yes - they should. Keep in mind that the zoo.cfg, and the ID file >>must >> >>be >> >> correct and in agreement on each instance. You can do a stat on each >> >> instance to see what state it's in: >> >> >> >> >telnet localhost 2181 >> >> stat >> >> >> >> -JZ >> >> >> >> On 5/8/12 2:43 PM, "Something Something" <[email protected]> >> >>wrote: >> >> >> >> >Thanks Jordan. Will definitely look at the cluster management tool. >> >>In >> >> >the mean time, am I correct with my assumption in #4? Once all of >>them >> >> >are >> >> >started they would automagically start talking to each other, right? >> >> > >> >> > >> >> >On Tue, May 8, 2012 at 2:36 PM, Jordan Zimmerman >> >> ><[email protected]>wrote: >> >> > >> >> >> Yes, you must start them all individually. ZooKeeper does not >> >>currently >> >> >> have any cluster-wide management tools built in. >> >> >> >> >> >> FYI - we've open sourced a cluster management tool for ZooKeeper. >> >>Please >> >> >> have a look: >> >> >> >> >> >> https://github.com/Netflix/exhibitor >> >> >> >> >> >> On 5/8/12 2:31 PM, "Something Something" >><[email protected]> >> >> >>wrote: >> >> >> >> >> >> >Hello, >> >> >> > >> >> >> >Trying to follow directions from here: >> >> >> > >> >> >> >> >> >> >> >> >> >> >> >>http://zookeeper.apache.org/doc/trunk/zookeeperAdmin.html#sc_zkMulitServe >> >> >>r >> >> >> >Setup >> >> >> > >> >> >> >to setup a cluster of zookeepers. >> >> >> > >> >> >> >Questions: >> >> >> > >> >> >> >1) If everything is setup correctly, do I have to go to each >> >>machine >> >> >>and >> >> >> >start Zookeeper server in each of them individually? >> >> >> >2) I was thinking if I start it on one master machine (well >> >>there's no >> >> >> >real master) then all zookeepers in the quorum would be started, >>but >> >> >>this >> >> >> >is not how it works correct? >> >> >> >3) If I start individually, then I get messages saying the other >> >> >> >zookeepers haven't started. Is that just a warning? >> >> >> >4) When all of them are started, would they all be able to talk >>to >> >> >>each >> >> >> >other? >> >> >> > >> >> >> >Sorry for the dumb questions and thanks for the help. >> >> >> >> >> >> >> >> >> >> >> >>
