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From "Bikas Saha (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4942) Add retry cache support in Namenode
Date Wed, 03 Jul 2013 06:34:23 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4942?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13698674#comment-13698674
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Bikas Saha commented on HDFS-4942:
----------------------------------

Some clarifications would be good
1) User runs create command using CLI. Internally, the command is tried many times over RPC.
Will these retries have the same UUID and will result in response coming from retry cache?
I think yes.
2) Client in 1) above tries many times and fails. User retries the CLI command again. This
will generate a new set of retries. Will these have the same UUID as the retries in 1) above.
Will they get response from retry cache?
                
> Add retry cache support in Namenode
> -----------------------------------
>
>                 Key: HDFS-4942
>                 URL: https://issues.apache.org/jira/browse/HDFS-4942
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: ha, namenode
>            Reporter: Suresh Srinivas
>            Assignee: Suresh Srinivas
>         Attachments: HDFSRetryCache.pdf
>
>
> In current HA mechanism with FailoverProxyProvider and non HA setups with RetryProxy
retry a request from the RPC layer. If the retried request has already been processed at the
namenode, the subsequent attempts fail for non-idempotent operations such as  create, append,
delete, rename etc. This will cause application failures during HA failover, network issues
etc.
> This jira proposes adding retry cache at the namenode to handle these failures. More
details in the comments.

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