Wei-Chiu Chuang commented on HDFS-11333:

Thanks for the review, [~linyiqun]!
Incidentally, I also found the same plugin configuration for DataNode, and a 
DataNode can also fail to start for the same reason (configuration key: 

Do you think DataNode should also log a warning and proceed if plugins can't be 

> Namenode unable to start if plugins can not be found
> ----------------------------------------------------
>                 Key: HDFS-11333
>                 URL: https://issues.apache.org/jira/browse/HDFS-11333
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 0.21.0
>            Reporter: Wei-Chiu Chuang
>            Assignee: Wei-Chiu Chuang
>              Labels: supportability
>         Attachments: HDFS-11333.001.patch
> If NameNode is unable to find plugins (specified in dfs.namenode.plugins), it 
> terminates abruptly with the following stack trace:
> {quote}
> Failed to start namenode.
> java.lang.RuntimeException: java.lang.ClassNotFoundException: Class XXX not 
> found
>   at org.apache.hadoop.conf.Configuration.getClasses(Configuration.java:2178)
>   at 
> org.apache.hadoop.conf.Configuration.getInstances(Configuration.java:2250)
>   at 
> org.apache.hadoop.hdfs.server.namenode.NameNode.startCommonServices(NameNode.java:713)
>   at 
> org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:691)
>   at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:843)
>   at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:822)
>   at 
> org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1543)
>   at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1611)
> {quote}
> We should catch this exception, log a warning message and let it proceed, as 
> missing the third party library does not affect the functionality of 
> NameNode. We caught this bug during a CDH upgrade where a third party plugin 
> was not in the lib directory of the newer version of CDH.

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