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To: user@zookeeper.apache.org
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Subject: Re: ConnectionLossException
From: Chris Barlock <barlock@us.ibm.com>
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Date: Fri, 16 Jan 2015 20:13:58 -0500
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I implemented a retry of every ZK method call I make and the exceptions 
stopped.  I recognize that we are currently using an older ZK version 
(3.3.4) -- but is the current version better in this respect?  I got the 
email today about the new release of Curator.  I wonder why this is not 
part of the ZK offering if it makes ZK that much easier to use.  (I don't 
know that this is a true statement, but the Curator doc claims so.)

Chris

IBM Tivoli Systems
Research Triangle Park, NC
(919) 224-2240
Internet:  barlock@us.ibm.com


From:   Chris Barlock/Raleigh/IBM@IBMUS
To:     user@zookeeper.apache.org
Date:   01/15/2015 09:37 PM
Subject:        Re: ConnectionLossException


My ensemble is a single ZK node running on the same computer as the rest 
of my application.  I think it is a "good state" because my configuration 
data does get loaded into ZK. 

Does ZK create the ConnectionLossException if the session timed out and I 
tried to use it after this happened?  If so, it would be related to the 
timeout.  If not, what causes ConnectionLossException?

Chris

IBM Tivoli Systems
Research Triangle Park, NC
(919) 224-2240
Internet:  barlock@us.ibm.com


From:   "bit1129@163.com" <bit1129@163.com>
To:     "user@zookeeper.apache.org" <user@zookeeper.apache.org>
Date:   01/15/2015 09:18 PM
Subject:        Re: ConnectionLossException


Connection loss is not related with the session timeout. If it frequently 
ocurrs, then it indicates that the ensemble of zookeeper are not in a good 

state.


bit1129@163.com
 
From: Chris Barlock
Date: 2015-01-16 10:04
To: user
Subject: ConnectionLossException
We are currently using ZK 3.3.4, which is included in the version of Kafka 


we are using.  I'm seeing a number of exceptions like:
 
org.apache.zookeeper.KeeperException$ConnectionLossException: 
KeeperErrorCode = ConnectionLoss for /com
        at 
org.apache.zookeeper.KeeperException.create(KeeperException.java:90)
        at 
org.apache.zookeeper.KeeperException.create(KeeperException.java:42)
        at org.apache.zookeeper.ZooKeeper.exists(ZooKeeper.java:815)
        at org.apache.zookeeper.ZooKeeper.exists(ZooKeeper.java:843)
        at 
com.ibm.tivoli.ccm.config.rest.ConfigClient.setValueAtNode(ConfigClient.java:630)
 
My method setValueAtNode includes a call to this method before I make any 
zk (ZooKeeper) calls:
 
    private void connectZooKeeper() {
        final String methodName = "connectZooKeeper";
        trace.entry(CLASS_NAME, methodName);
        if (zk == null || zk.getState() != States.CONNECTED) {
            if (zk != null) {
                close();
            }
            try {
                zk = new ZooKeeper(connectString, sessionTimeout, this);
                int connectAttempts = 0;
                while (zk.getState() != States.CONNECTED && 
connectAttempts < MAX_ZK_CONNECT_ATTEMPTS) {
                    try {
                        Thread.sleep(ZK_CONNECT_WAIT);
                    } catch (InterruptedException e) {
                        // Ignore
                    }
                    connectAttempts++;
                }
            } catch (IOException e) {
                trace.exception(CLASS_NAME, methodName, e);
            }
        }
        trace.exit(CLASS_NAME, methodName); 
    }
 
I'm totally guessing that the connection is timing out between the time 
this method is called and when I make the following zk method calls.  Is 
there a best practise for ensuring one is connected to ZooKeeper?  My 
session timeout is 3000 ms.
 
Chris


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