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https://issues.apache.org/jira/browse/HDFS-6981?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14123413#comment-14123413
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Arpit Agarwal commented on HDFS-6981:
-------------------------------------
Lacking an explicit finalize command for rolling upgrade, it is hard for the DN
to determine when to delete 'previous'. Rolling upgrade is signaled by the
presence/absence of RollingUpgradeInfo in the heartbeat response.
Without modifying the NN, one solution is that the DN creates a marker file
when rolling upgrade is signaled by NN. When rolling upgrade is no longer
signaled by NN, 'previous' is cleaned up only if the marker file is present.
Else a regular upgrade is in progress and 'previous' is left alone.
I am wary of making NN changes, the interaction with HA is complex enough as it
is.
> DN upgrade with layout version change should not use trash
> ----------------------------------------------------------
>
> Key: HDFS-6981
> URL: https://issues.apache.org/jira/browse/HDFS-6981
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Affects Versions: 3.0.0
> Reporter: James Thomas
> Assignee: Arpit Agarwal
> Attachments: HDFS-6981.01.patch, HDFS-6981.02.patch,
> HDFS-6981.03.patch, HDFS-6981.04.patch
>
>
> Post HDFS-6800, we can encounter the following scenario:
> # We start with DN software version -55 and initiate a rolling upgrade to
> version -56
> # We delete some blocks, and they are moved to trash
> # We roll back to DN software version -55 using the -rollback flag – since we
> are running the old code (prior to this patch), we will restore the previous
> directory but will not delete the trash
> # We append to some of the blocks that were deleted in step 2
> # We then restart a DN that contains blocks that were appended to – since the
> trash still exists, it will be restored at this point, the appended-to blocks
> will be overwritten, and we will lose the appended data
> So I think we need to avoid writing anything to the trash directory if we
> have a previous directory.
> Thanks to [~james.thomas] for reporting this.
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