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https://issues.apache.org/jira/browse/HADOOP-7380?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Aaron T. Myers updated HADOOP-7380:
-----------------------------------

    Attachment: hadoop-7380.0.patch

Here's a first hack at the Common portion of client failover, not intended for 
commit.

If people think this approach is roughly sound I'll fix it up and prepare it 
for commit. It still needs at least the following work:

* A way to mark certain interface methods as idempotent (and thus should be 
retried upon failover). This will probably take the form of a method annotation.
* Refinement of the precise set of exceptions to deal with.
* Potential refinement of the {{FailoverProxyProvider}} interface. I'm not in 
love with it as it stands.

I've also created a test which uses this code to actually perform a failover 
between two federated NNs (which happen to have the same FS metadata) by 
starting them both up, creating a file in each at the same path, shutting down 
one, and ensuring the DFSClient properly fails over to the second. I can post 
that patch on HDFS-1973 but it depends on this patch.

> Common portion of HDFS-1973
> ---------------------------
>
>                 Key: HADOOP-7380
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7380
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: ipc
>    Affects Versions: 0.23.0
>            Reporter: Aaron T. Myers
>            Assignee: Aaron T. Myers
>             Fix For: 0.23.0
>
>         Attachments: hadoop-7380.0.patch
>
>
> Implementing client failover will likely require changes to {{o.a.h.io.ipc}} 
> and/or {{o.a.h.io.retry}}. This JIRA is to track those changes.

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