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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-9792) Retry the methods that are tagged @AtMostOnce along with @Idempotent
Date Tue, 30 Jul 2013 18:45:49 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9792?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13724244#comment-13724244
] 

Suresh Srinivas commented on HADOOP-9792:
-----------------------------------------

bq.  I think better would be to just mark these Idempotent and put a comment on the methods
that the reason for that is because errant retries will be detected by the retry cache.
This is an incorrect hack. The methods that are annotated with @AtMostOnce are "non-idempotent"
operations.

To follow the discussion on difference between Idempotent and request that can be replayed/retried
by a single client, see the discussion in HDFS-4849. The difference have been discussed to
death in that jira.

Also see extensive analysis of Namenode protocols and adding annotation @AtMostOnce for "non-idempotent"
operations in HDFS-4974, that was done over a period of 4 weeks! Not to mention all the other
operations that are made idempotent to make HA finally work correctly without boundary condition
application failures.

@AtMostOnce != @Idempotent
Also the methods without these annotations will not be retried.
                
> Retry the methods that are tagged @AtMostOnce along with @Idempotent
> --------------------------------------------------------------------
>
>                 Key: HADOOP-9792
>                 URL: https://issues.apache.org/jira/browse/HADOOP-9792
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: ipc
>            Reporter: Suresh Srinivas
>            Assignee: Suresh Srinivas
>             Fix For: 2.1.0-beta
>
>         Attachments: HADOOP-9792.1.patch, HADOOP-9792.patch
>
>
> Currently the operations marked as @Idempotent are retried. Now that we have added new
operations that are marked @AtMostOnce that guaranteed to be executed only once with the help
of RetryCache on server implementation, these methods should also be retried.

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