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From "Enis Soztutar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-3787) Increment is non-idempotent but client retries RPC
Date Mon, 22 Apr 2013 21:21:15 GMT

    [ https://issues.apache.org/jira/browse/HBASE-3787?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13638441#comment-13638441
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Enis Soztutar commented on HBASE-3787:
--------------------------------------

So, Hadoop seems to be trying to solve the problem in some basic cases by inspecting the exceptions,
but in the end, if it cannot reason about whether the operation has already succeeded it will
throw the exception to the user. Basically, throwing ItsNotMyProblemItsYourProblemExceptionâ„¢.

Depending on how critical to have correct idempotent semantics (especially for distributed
counters), I would be ok with going with the basic hash, or not-retrying across-servers solution
for 0.96, and implement one of the proposals above (or some other solution) on a longer timeframe.

                
> 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: 0.94.4, 0.95.2
>            Reporter: dhruba borthakur
>            Assignee: Sergey Shelukhin
>            Priority: Critical
>             Fix For: 0.95.1
>
>         Attachments: HBASE-3787-partial.patch
>
>
> 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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