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https://issues.apache.org/jira/browse/ZOOKEEPER-251?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12654870#action_12654870
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Mahadev konar commented on ZOOKEEPER-251:
-----------------------------------------

sorry i must have been confused. I though the servers were started as quorum 
and then one of them pulled out of quorum and started as a standalone server. 
This will actually create the problem quote easily. The 3 quorum servers and 
killing one at a time is another way to do it (now that i realize it).

> NullPointerException stopping and starting Zookeeper servers
> ------------------------------------------------------------
>
>                 Key: ZOOKEEPER-251
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-251
>             Project: Zookeeper
>          Issue Type: Bug
>          Components: server
>    Affects Versions: 3.0.0, 3.0.1
>         Environment: Tested with JDK 1.5, Solaris, but I suspect it is not 
> relevant in this case.
>            Reporter: Thomas Vinod Johnson
>            Assignee: Mahadev konar
>            Priority: Blocker
>             Fix For: 3.1.0
>
>         Attachments: ZOOKEEPER-251.patch
>
>
> See the following thread for the original report:
> http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-user/200812.mbox/browser
> Steps to reproduce:
> 1) Start a replicated zookeeper service consisting of 3 zookeeper (3.0.1) 
> servers all running on the same host (of course, all using their own ports 
> and log directories)
> 2) Create one znode in this ensemble (using the zookeeper client console, I 
> issued 'create /node1 node1data').
> 3) Stop, then restart a single zookeeper server; moving onto the next one a 
> few seconds later. 
> 4) Go back to 3. After 4-5 iterations, the following should occur, with the 
> failing server exiting:
> java.lang.NullPointerException
>         at 
> org.apache.zookeeper.server.persistence.FileTxnLog$FileTxnIterator.next(FileTxnLog.java:447)
>         at 
> org.apache.zookeeper.server.persistence.FileTxnLog$FileTxnIterator.init(FileTxnLog.java:358)
>         at 
> org.apache.zookeeper.server.persistence.FileTxnLog$FileTxnIterator.<init>(FileTxnLog.java:333)
>         at 
> org.apache.zookeeper.server.persistence.FileTxnLog.read(FileTxnLog.java:250)
>         at 
> org.apache.zookeeper.server.persistence.FileTxnSnapLog.restore(FileTxnSnapLog.java:102)
>         at 
> org.apache.zookeeper.server.ZooKeeperServer.loadData(ZooKeeperServer.java:183)
>         at org.apache.zookeeper.server.quorum.Leader.lead(Leader.java:245)
>         at 
> org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:421)
> 2008-12-08 14:14:24,880 - INFO  
> [QuorumPeer:/0:0:0:0:0:0:0:0:2183:[EMAIL PROTECTED] - Shutdown called
> java.lang.Exception: shutdown Leader! reason: Forcing shutdown
>         at 
> org.apache.zookeeper.server.quorum.Leader.shutdown(Leader.java:336)
>         at 
> org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:427)
> Exception in thread "QuorumPeer:/0:0:0:0:0:0:0:0:2183" 
> java.lang.NullPointerException
>         at 
> org.apache.zookeeper.server.quorum.Leader.shutdown(Leader.java:339)
>         at 
> org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:427)
> The inputStream field is null, apparently because next is being called 
> at line 358 even after next returns false. Having very little knowledge 
> about the implementation, I don't know if the existence of hdr.getZxid() 
>  >= zxid is supposed to be an invariant across all invocations of the 
> server; however the following change to FileTxnLog.java seems to make 
> the problem go away.
> diff FileTxnLog.java /tmp/FileTxnLog.java
> 358c358,359
> <                 next();
> ---
>  >               if (!next())
>  >                   return;
> 447c448,450
> <                 inputStream.close();
> ---
>  >               if (inputStream != null) {
>  >                   inputStream.close();
>  >               }

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