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https://issues.apache.org/jira/browse/ZOOKEEPER-2867?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16117570#comment-16117570
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Jun Rao edited comment on ZOOKEEPER-2867 at 8/7/17 11:50 PM:
-------------------------------------------------------------

[~hanm], thanks for the reply. I am attaching the log of 2 of the 3 ZK servers 
around that time. During that window, there was some potential network issue 
that may prevent ZK servers from talking to each other. The network issue seems 
to be gone after 22:05:20, when the ZK cluster stabilized again.

Assuming that session 25cd1e82c110001 didn't really get expired at that point, 
I got a followup question. A month later, the whole ZK cluster was done and was 
restarted. On restarting, I saw the following logging in ZK server about 
deleting an ephemeral in that session. 


{code:java}
August 2nd 2017, 23:41:55.076   DEBUG   org.apache.zookeeper.server.DataTree    
Deleting ephemeral node /cp15/brokers/ids/0 for session 0x25cd1e82c110001 
{code}

I assume that's because ZK server thinks that session is expired? However, in 
ZK server's commit log, I didn't find any entry about closing that session. Is 
that normal? Thanks,


was (Author: junrao):
[~hanm], thanks for the reply. I am attaching the log of 2 of the 3 ZK servers 
around that time. During that window, there was some potential network issue 
that may prevent ZK servers from talking to each other. The network issue seems 
to be gone after 22:05:20, when the ZK cluster stabilized again.

Assuming that session 25cd1e82c110001 didn't really get expired at that point, 
I got a followup question. A month later, the whole ZK cluster was done and was 
restarted. On restarting, I saw the following logging in ZK server about 
deleting an ephemeral in that session. 

August 2nd 2017, 23:41:55.076   DEBUG   org.apache.zookeeper.server.DataTree    
Deleting ephemeral node /cp15/brokers/ids/0 for session 0x25cd1e82c110001 

I assume that's because ZK server thinks that session is expired? However, in 
ZK server's commit log, I didn't find any entry about closing that session. Is 
that normal? Thanks,

> an expired ZK session can be re-established
> -------------------------------------------
>
>                 Key: ZOOKEEPER-2867
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2867
>             Project: ZooKeeper
>          Issue Type: Bug
>    Affects Versions: 3.4.10
>            Reporter: Jun Rao
>         Attachments: zk.0.formatted, zk.1.formatted
>
>
> Not sure if this is a real bug, but I found an instance when a ZK client 
> seems to be able to renew a session already expired by the ZK server.
> From ZK server log, session 25cd1e82c110001 was expired at 22:04:39.
> {code:java}
> June 27th 2017, 22:04:39.000  INFO    
> org.apache.zookeeper.server.ZooKeeperServer     Expiring session 
> 0x25cd1e82c110001, timeout of 12000ms exceeded
> June 27th 2017, 22:04:39.001  DEBUG   
> org.apache.zookeeper.server.quorum.Leader       Proposing:: 
> sessionid:0x25cd1e82c110001 type:closeSession cxid:0x0 zxid:0x200000fc4 
> txntype:-11 reqpath:n/a
> June 27th 2017, 22:04:39.001  INFO    
> org.apache.zookeeper.server.PrepRequestProcessor        Processed session 
> termination for sessionid: 0x25cd1e82c110001
> June 27th 2017, 22:04:39.001  DEBUG   
> org.apache.zookeeper.server.quorum.CommitProcessor      Processing request:: 
> sessionid:0x25cd1e82c110001 type:closeSession cxid:0x0 zxid:0x200000fc4 
> txntype:-11 reqpath:n/a
> June 27th 2017, 22:05:20.324  INFO    
> org.apache.zookeeper.server.quorum.Learner      Revalidating client: 
> 0x25cd1e82c110001
> June 27th 2017, 22:05:20.324  INFO    
> org.apache.zookeeper.server.ZooKeeperServer     Client attempting to renew 
> session 0x25cd1e82c110001 at /100.96.5.6:47618
> June 27th 2017, 22:05:20.325  INFO    
> org.apache.zookeeper.server.ZooKeeperServer     Established session 
> 0x25cd1e82c110001 with negotiated timeout 12000 for client /100.96.5.6:47618
> {code}
> From ZK client's log, it was able to renew the expired session on 22:05:20.
> {code:java}
> June 27th 2017, 22:05:18.590  INFO    org.apache.zookeeper.ClientCnxn Client 
> session timed out, have not heard from server in 4485ms for sessionid 
> 0x25cd1e82c110001, closing socket connection and attempting reconnect      0
> June 27th 2017, 22:05:18.590  WARN    org.apache.zookeeper.ClientCnxn Client 
> session timed out, have not heard from server in 4485ms for sessionid 
> 0x25cd1e82c110001  0
> June 27th 2017, 22:05:19.325  WARN    org.apache.zookeeper.ClientCnxn SASL 
> configuration failed: javax.security.auth.login.LoginException: No JAAS 
> configuration section named 'Client' was found in specified JAAS 
> configuration file: '/opt/confluent/etc/kafka/server_jaas.conf'. Will 
> continue connection to Zookeeper server without SASL authentication, if 
> Zookeeper server allows it. 0
> June 27th 2017, 22:05:19.326  INFO    org.apache.zookeeper.ClientCnxn Opening 
> socket connection to server 100.65.188.168/100.65.188.168:2181  0
> June 27th 2017, 22:05:20.324  INFO    org.apache.zookeeper.ClientCnxn Socket 
> connection established to 100.65.188.168/100.65.188.168:2181, initiating 
> session 0
> June 27th 2017, 22:05:20.327  INFO    org.apache.zookeeper.ClientCnxn Session 
> establishment complete on server 100.65.188.168/100.65.188.168:2181, 
> sessionid = 0x25cd1e82c110001, negotiated timeout = 12000  0
> {code}



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