[jira] [Commented] (HDFS-4942) Add retry cache support in Namenode

["Chris Nauroth (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-4942?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13698423#comment-13698423 ] 

Chris Nauroth commented on HDFS-4942:
-------------------------------------

The proposal looks good, and I'll be interested to see the analysis of the individual RPC calls.  Reminder on something that came up in offline conversation: it appears that we can change {{ClientProtocol#getDataEncryptionKey}} to annotate it as Idempotent.  It doesn't appear to mutate state.  If a retry causes creation of multiple keys, that shouldn't be a problem.

{quote}
Given that we plan on adding a unique identifier to every RPC request, should we get this change done before 2.1.0-beta rc2 is built? This way 2.1.0-beta clients can utilize retry cache as well.
{quote}

+1 for this idea.  Adding the UUID now would be a low-risk change.
                
> 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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