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https://issues.apache.org/jira/browse/HDFS-6005?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13910747#comment-13910747
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Arpit Agarwal commented on HDFS-6005:
-------------------------------------
Hi Suresh,
The patch looks good. The new approach is much nicer. Minor points, +1
otherwise.
# {{restoreBlockFilesFromTrash}} - the initialization {{File restoreDirectory =
null;}} was intended to be outside the for loop. This avoids recomputing
{{restoreDirectory}} for each child of the same {{trashRoot}}. The move looks
unintentional since there is an assignment to null followed by a check for null.
# Nitpick - Incomplete comment in TestDataNodeRollingUpgrade.java: {{// Ensure
trash is}}.
> 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
> Attachments: HDFS-6005.01.patch, HDFS-6005.02.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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