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https://issues.apache.org/jira/browse/HDFS-7926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14359769#comment-14359769
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Tsz Wo Nicholas Sze commented on HDFS-7926:
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There are two solutions:
# change ClientProtocol.truncate to @AtMostOnce; or
# change NameNode implementation of ClientProtocol.truncate(..) to idempotent.

I think #2 is an easy and better solution.

> NameNode implementation of ClientProtocol.truncate(..) is not idempotent
> ------------------------------------------------------------------------
>
>                 Key: HDFS-7926
>                 URL: https://issues.apache.org/jira/browse/HDFS-7926
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>            Reporter: Tsz Wo Nicholas Sze
>            Assignee: Tsz Wo Nicholas Sze
>
> If dfsclient drops the first response of a truncate RPC call, the retry by 
> retry cache will fail with "DFSClient ... is already the current lease 
> holder".  The truncate RPC is annotated as @Idempotent in ClientProtocol but 
> the NameNode implementation is not.



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