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https://issues.apache.org/jira/browse/HDFS-7926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14361389#comment-14361389
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Yi Liu commented on HDFS-7926:
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Thanks [~szetszwo] for the fix. Actually I agree that {{idempotent}} is good as
you said.
But the trouble issue is lease check/recovery for truncate, we just want to
make sure the truncate retries get the same result. I have found one case that
currently fix can't cover:
# Client invokes truncate, but it's on block boundary, so we will not add lease
and there is no block recovery. And the result should be *true*.
# Meanwhile network issue for the client, and retry happens after few time.
# Before retry happen or before it arrives NN, some other client invokes append
on this file.
# Then NN receives the retry, so there is lease failure.
# Actually the truncate is successful, but client sees failure.
> 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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