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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4942) Add retry cache support in Namenode
Date Tue, 16 Jul 2013 17:42:50 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4942?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13709972#comment-13709972
] 

Konstantin Shvachko commented on HDFS-4942:
-------------------------------------------

Using clientId for multiplexing RPC connections is an interesting use case. Check the uniqueness
guarantees though.

> The current solution will be useful for all the other applications

Is that a hypothetical opportunity or you have any particular use cases in mind for Yarn?
Would be good to know.

>> avoid incompatible RPC changes that effect sub-projects
> I am not sure what you mean by this.

I mean that you are building a retry cache for HDFS and making changes incompatible for all
other projects (rather than for HDFS only). So I am trying to understand what value it brings
to others.
                
> 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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