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From "Arpit Agarwal (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (HDFS-6005) Simplify Datanode rollback and downgrade
Date Mon, 24 Feb 2014 20:48:23 GMT

     [ https://issues.apache.org/jira/browse/HDFS-6005?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Arpit Agarwal resolved HDFS-6005.

       Resolution: Fixed
    Fix Version/s: HDFS-5535 (Rolling upgrades)
     Hadoop Flags: Reviewed

+1 for the updated patch.

I committed it to the feature branch as r1571431. Thanks Suresh!

> Simplify Datanode rollback and downgrade
> ----------------------------------------
>                 Key: HDFS-6005
>                 URL: https://issues.apache.org/jira/browse/HDFS-6005
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: datanode, namenode
>            Reporter: Suresh Srinivas
>            Assignee: Suresh Srinivas
>             Fix For: HDFS-5535 (Rolling upgrades)
>         Attachments: HDFS-6005.01.patch, HDFS-6005.02.patch, HDFS-6005.03.patch, HDFS-6005.patch
> Problem:
> When rolling upgrade fails, the cluster can either be downgraded or rolled back. With
the current functionality in this feature branch, it is possible to downgrade namenode, while
datanode is incorrectly rolled back. This does not affect the cluster state. The old blocks
that appear back on the datanode due to rollback will be deleted. Similarly it is also possible
to rollback namenode, while datanode is not rolled back. This can cause problem where old
blocks do not appear back on the datanode and can result in missing blocks.
> Solution:
> I propose making the following changes:
> During rollback or downgrade, the entire cluster must be restarted. The datanodes always
restore the deleted blocks on restart and go back to trash disabled mode. There is no need
for datanodes to be started up -rollingUpgrade -rollback, anymore.
> # On namenode downgrade, the restored blocks are deleted.
> # On namenode rollback, the restored blocks will be retained and any newly created blocks
(since the start of rolling upgrade) are deleted.
> This is much simpler operationally and solves the problem described above.

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