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Date: Mon, 08 Dec 2008 11:48:02 -0800
Subject: Re: NullPointerException stopping and starting Zookeeper servers
From: Mahadev Konar <mahadev@yahoo-inc.com>
To: <zookeeper-user@hadoop.apache.org>
Message-ID: <C562B9F2.15569%mahadev@yahoo-inc.com>
Thread-Topic: NullPointerException stopping and starting Zookeeper servers
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In-Reply-To: <493D7684.9050301@sun.com>
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Hi Thomas,
 This looks like a bug. Can you open a jira mentioning what the problem is
and how to recreate it?

Thanks
mahadev


On 12/8/08 11:33 AM, "Thomas Vinod Johnson" <Thomas.Johnson@Sun.COM> wrote:

> Hi,
> I have a replicated zookeeper services consisting of 3 zookeeper (3.0.1)
> servers all running on the same host for testing purposes. I've created
> exactly one znode in this ensemble. At this point, I stop, then restart
> a single zookeeper server; moving onto the next one a few seconds later.
> A few restarts later (about 4 is usually sufficient), I get the
> following exception on one of the servers, at which point it exits:
> java.lang.NullPointerException
>         at 
> org.apache.zookeeper.server.persistence.FileTxnLog$FileTxnIterator.next(FileTx
> nLog.java:447)
>         at 
> org.apache.zookeeper.server.persistence.FileTxnLog$FileTxnIterator.init(FileTx
> nLog.java:358)
>         at 
> org.apache.zookeeper.server.persistence.FileTxnLog$FileTxnIterator.<init>(File
> TxnLog.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:Leader@336] - 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();
>>               }
> 
> Is this a bug?
> 
> Thanks.
>