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https://issues.apache.org/jira/browse/HBASE-3787?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13567401#comment-13567401
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Enis Soztutar commented on HBASE-3787:
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BTW, having an in-memory windowing view of latest nonces only solves most of 
the issues. But imagine the case, where client does increment, it is processed 
successfully in region, appended to WAL, but server failed before returning 
response. Client retries on the new server, which does not know about this 
nonce, so happily accepts the duplicate increment. To do true idempotency, we 
should append the nonce to the WALEdit. 
                
> Increment is non-idempotent but client retries RPC
> --------------------------------------------------
>
>                 Key: HBASE-3787
>                 URL: https://issues.apache.org/jira/browse/HBASE-3787
>             Project: HBase
>          Issue Type: Bug
>          Components: Client
>    Affects Versions: 0.96.0, 0.94.4
>            Reporter: dhruba borthakur
>            Priority: Critical
>             Fix For: 0.96.0
>
>
> The HTable.increment() operation is non-idempotent. The client retries the 
> increment RPC a few times (as specified by configuration) before throwing an 
> error to the application. This makes it possible that the same increment call 
> be applied twice at the server.
> For increment operations, is it better to use 
> HConnectionManager.getRegionServerWithoutRetries()? Another  option would be 
> to enhance the IPC module to make the RPC server correctly identify if the 
> RPC is a retry attempt and handle accordingly.

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