Storing and Configuring Data with Hadoop, YARN, and ZooKeeper - Big Data Made Easy: A Working Guide to the Complete Hadoop Toolset - page 39

Now, I use get to set a watcher on that node. The first command sets a watcher on the node2 data item “data2.”
When I change the data to “data3” with the next set command, the watcher notices the data change and fires, as shown:
[zk: localhost:2181(CONNECTED) 11] get /zk-top/node2 true
'data2'
[zk: localhost:2181(CONNECTED) 12] set /zk-top/node2 'data3'
WATCHER::
WatchedEvent state:SyncConnected type:NodeDataChanged path:/zk-top/node2
In addition to the basic nodes you've been working with, you can create sequential and ephemeral nodes with
the create command. Ephemeral nodes exist only for the lifetime of the current session, while sequential nodes have a
sequence number applied to the node name and will persist. To create a sequential node, use the -s option, as shown:
[zk: localhost:2181(CONNECTED) 13] ls /zk-top
[node2, node1]
[zk: localhost:2181(CONNECTED) 14] create -s /zk-top/node3 'data3'
Created /zk-top/node30000000005
[zk: localhost:2181(CONNECTED) 15] ls /zk-top
[node2, node1, node30000000005]
To create an ephemeral node, use the -e option:
[zk: localhost:2181(CONNECTED) 16] create -e /zk-top/node4 'data4'
Created /zk-top/node4
[zk: localhost:2181(CONNECTED) 17] ls /zk-top
[node4, node2, node1, node30000000005]
So, node 4 exists in this session under zk-top. It will disappear when you log out of the session (with quit ) and
start a new one. Notice that the ls command at the end of this sequence no longer lists node4:
[zk: localhost:2181(CONNECTED) 18] quit
Quitting...
2014-03-22 14:02:56,572 [myid:] - INFO [main:ZooKeeper@684] - Session: 0x344e6df92ab0005 closed
2014-03-22 14:02:56,572 [myid:] - INFO [main-EventThread:ClientCnxn$EventThread@512] - EventThread
shut down
[hadoop@hc1r1m3 ~]$
[hadoop@hc1r1m3 ~]$ zookeeper-client
[zk: localhost:2181(CONNECTED) 0] ls /zk-top
[node2, node1, node30000000005]
As you can see, node 4 is gone; it only existed for the session in which it was created. Note: you can also make
sequential nodes ephemeral with a command like this:
[zk: localhost:2181(CONNECTED) 16] create -s -e /zk-top/node4 'data4'