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https://issues.apache.org/jira/browse/HDFS-15115?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17014317#comment-17014317
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xuzq commented on HDFS-15115:
-----------------------------
Thanks [~wzx513] for the report, I met this bug too.
I set the log level of BlockPlacementPolicyDefault from INFO to DEBUG by
LogLevel to confirm somethings when the nameNode is running, but the nameNode
crashed by NPE in *builder.append()*.
Checked the code and found, the *builder* may be not inited because the LOG
level is INFO, but it be used after I set the LOG level to DEBUG by LogLevel.
{code:java}
StringBuilder builder = null;
if (LOG.isDebugEnabled()) {
// it not be inited, because the LOG is not debugEnable.
builder = debugLoggingBuilder.get();
builder.setLength(0);
builder.append("[");
}
if (LOG.isDebugEnabled()) {
// it will be used, because i set the LOG level from INFO to DEBUG by
LogLevel.
builder.append("\nNode ").append(NodeBase.getPath(chosenNode))
.append(" [");
}
{code}
[~belugabehr] do you have time to review this patch? I found you are more
familiar with this logic, thanks.
> Namenode crash caused by NPE in BlockPlacementPolicyDefault when dynamically
> change logger to debug
> ---------------------------------------------------------------------------------------------------
>
> Key: HDFS-15115
> URL: https://issues.apache.org/jira/browse/HDFS-15115
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: wangzhixiang
> Priority: Major
> Attachments: HDFS-15115.001.patch
>
>
> To get debug info, we dynamically change the logger of
> BlockPlacementPolicyDefault to debug when namenode is running. However, the
> Namenode crashs. From the log, we find some NPE in
> BlockPlacementPolicyDefault.chooseRandom. Because *StringBuilder builder*
> will be used 4 times in BlockPlacementPolicyDefault.chooseRandom method.
> While the *builder* only initializes in the first time of this method. If we
> change the logger of BlockPlacementPolicyDefault to debug after the part, the
> *builder* in remaining part is *NULL* and cause *NPE*
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