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https://issues.apache.org/jira/browse/HDFS-4849?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13705281#comment-13705281
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Konstantin Shvachko commented on HDFS-4849:
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> In Hadoop summit we agreed that this change will not make create idempotent. 
> You are only enabling retry

I am not arguing, as we agreed.
We also agreed that create retry is worth using in order to minimize the retry 
cache size. As an optimization.

> please consider updating the jira description accordingly.

Let me know how you want it to be.

> How did you solve the issue of two threads in a single client calling create?

As I argued before this is a common problem with retries or without. And the 
solution is to guarantee unique client names, which should be done in a 
different jira. If I understood your question correctly.

> Please see my analysis of namenode operations in HDFS-4974.

Very good analysis. Thanks.

> I feel we should use retry cache instead of doing a separate retry support 
> for create alone.

This is not what agreed upon at the Summit. Let me know if you changed your 
mind.
                
> Idempotent create and append operations.
> ----------------------------------------
>
>                 Key: HDFS-4849
>                 URL: https://issues.apache.org/jira/browse/HDFS-4849
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 2.0.4-alpha
>            Reporter: Konstantin Shvachko
>            Assignee: Konstantin Shvachko
>            Priority: Blocker
>         Attachments: idempotentCreate-branch2.patch, idempotentCreate.patch, 
> idempotentCreate.patch, idempotentCreate.patch, idempotentCreate.patch
>
>
> create, append and delete operations can be made idempotent. This will reduce 
> chances for a job or other app failures when NN fails over.

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