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https://issues.apache.org/jira/browse/HDFS-7926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14361481#comment-14361481
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Tsz Wo Nicholas Sze commented on HDFS-7926:
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"idempotent" means applying the same operations multiple times will get the
same result. If there is an append in the middle, the retry could get
different results.
E.g. getPermission is idempotent. However, if there is a setPermission (or
delete, rename, etc.) in the middle, the retry of getPermission could get a
different result.
> 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
> Fix For: 2.7.0
>
> Attachments: h7926_20150313.patch, h7926_20150313b.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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