In this case all of the _other_ zookeeper clients will see the client session is closed (actually they see any ephemeral znodes that the client created are removed, which is typically what you do for group membership - create an ephemeral znode that represents your client, a member of the cluster) and can act appropriately.

Your client will see a disconnected event:

Given what Mahadev mentioned (you don't know if you are expired until you reconnect) what you do now in the disco client is up to your use case. If it's just group membership then it's probably fine, your client will be disconnected, perhaps expired. It won't know, but the rest of the cluster (incl any monitoring app) will know and can act appropriately. The disconnected client needs to decide what to do (perhaps, or perhaps it doesn't do anything, it's just that the other members of the cluster no longer consider it active, and therefore don't involve it in processing)


neptune wrote:
I saw that wiki page. And I read this paragraph "It means that the client
was partitioned off from the ZooKeeper service for more the the session
timeout ..."
That's why I use Expired event for cluster membership. In my case client is
a node in a cluster.

2010/2/9 Patrick Hunt <>

this? "How should I handle SESSION_EXPIRED?"

Benjamin Reed wrote:

i was looking through the docs to see if we talk about handling session
expired, but i couldn't find anything. we should probably open a jira to add
to the docs, unless i missed something. did i?


-----Original Message-----
From: Mahadev Konar [] Sent: Monday, February
08, 2010 2:43 PM
Subject: Re: When session expired event fired?

 a zookeeper client does not expire a session until and unless it is able
connect to one of the servers. In your case if you kill all the servers,
client is not able to connect to any of the servers and will keep trying
connect to the three servers. It cannot expire a session on its own and
needs to hear from the server to know if the session is expired or not.

Does that help?

On 2/8/10 2:37 PM, "neptune" <> wrote:

 Hi all.
I have a question. I started zookeeper(3.2.2) on three servers.
When session expired event fired in following code?
I expected that if client can't connect to server(disconnected) for
timeout, zookeeper fires session expired event.
I killed three zookeeper server sequentially. Client retry to connect
zookeeper server. Never occured Expired event.

*class WatcherTest {
 public static void main(String[] args) {
   (new **WatcherTest*()).exec();
*  }

 private WatcherTest() throws Exception {
   zk = new ZooKeeper("server1:2181,server2:2181:server3:2181", 10 *
 private void exec() {
   while(ture) {
     //do something
 public void process(WatchedEvent event) {
   if (event.getType() == Event.EventType.None) {
     switch (event.getState()) {
     case SyncConnected:
       System.out.println("ZK SyncConnected");
     case Disconnected:
       System.out.println("ZK Disconnected");
     case Expired:
       System.out.println("ZK Session Expired");

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