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https://issues.apache.org/jira/browse/HDFS-4974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13708884#comment-13708884
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Chris Nauroth commented on HDFS-4974:
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{quote}
Given the entire metasave is done with writeLock() held, will this be an issue?
Currently one could have two metasaves issued by two clients right? Given that
I think it should be okay to mark it as idempotent?
{quote}
Holding the write lock keeps the operation thread-safe (multiple concurrent
calls won't corrupt state), but not idempotent, because repeated calls yield
side effects (one copy of the data in the file vs. multiple).
It is correct that 2 clients requesting a metasave to the same output file
would also cause this problem. This is slightly different in that it's not
retries of the exact same RPC call.
I suggest that we switch to opening the output file with overwrite instead of
append to make it truly idempotent. If that change is seen as too risky, then
we could apply the retry cache to this call.
> Analyze and add annotations to Namenode and Datanode protocol methods to
> enable retry
> -------------------------------------------------------------------------------------
>
> Key: HDFS-4974
> URL: https://issues.apache.org/jira/browse/HDFS-4974
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: ha, namenode
> Reporter: Suresh Srinivas
>
> This jira is intended for:
> # Discussing current @Idempotent annotations in HDFS protocols and adding
> that annotation where it is missing.
> # Discuss how retry should be enabled for non-idempotent requests.
> I will post the analysis of current methods in subsequent comment.
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