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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4942) Add retry cache support in Namenode
Date Fri, 28 Jun 2013 21:51:20 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4942?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13695837#comment-13695837

Suresh Srinivas commented on HDFS-4942:

This issue was discussed in HadoopSummit 2013, HDFS Design Lounge. Folks participated in the
discussion agreed about the need for retry cache. Here are some high level decisions:
# Retry cache will be added to the namenode for idempotent operations. An entry in retry cache
will be retained for configurable period of time. It will track non-idempotent requests when
they successfully complete.
# To identify a request uniquely, currently RPC call ID is not sufficient. Additional identifiers
will be added to RPC to uniquely identify requests coming from the same client, two clients
on the same machine and two clients on different machines.

I will post a design by early next week.
> 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
> 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 idempotent operations such as  create, append,
delete, rename etc. This will cause application failures during HA failover, network issues
> This jira proposes adding retry cache at the namenode to handle these failures. More
details in the comments.

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