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https://issues.apache.org/jira/browse/HDFS-7926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14359966#comment-14359966
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Jitendra Nath Pandey commented on HDFS-7926:
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[~szetszwo], I think the patch works correctly and returns false if the
truncate is called the second time. But for a file being written or appended,
truncate will still return false if the oldlength happens to be same as
newlength. It should throw an exception in this scenario. In this approach, it
seems there is a need to distinguish whether file is under construction due to
a truncate or due to a create/append.
> 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
> Attachments: h7926_20150313.patch
>
>
> 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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