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https://issues.apache.org/jira/browse/HDFS-5907?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13898871#comment-13898871
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Arpit Agarwal commented on HDFS-5907:
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Hi Suresh, I described it in earlier comment. The approach is the same.
{quote}
The patch adds a trash directory under BlockPoolSliceStorage. The trash
directory location is SD/current/BP-.../trash/ and its sub-directory layout
mirrors that of SD/current/BP-.../current/. This allows keeping memory of where
to restore the file on rollback.
An alternative is to just rename the file under its current location to
indicate it is a deleted block but this makes finalize and rollback expensive
as we may have to potentially iterate over millions of block files.
The DN detects whether a rolling upgrade is in progress or not by looking for
the presence of RollingUpgradeStatus in HeartbeatResponse.
If a block is deleted for a BPID undergoing rolling upgrade then it is moved to
a trash directory instead. On finalize the trash directory is emptied. On
rollback, files under trash/ are restored to their corresponding locations
under current/.
{quote}
The only addition is that DN rollback is triggered by passing a
{{-rollingUpgrade rollback}} flag at startup. This was chosen to be the same as
the flag passed to NN for rollback.
> Handle block deletion requests during rolling upgrades
> ------------------------------------------------------
>
> Key: HDFS-5907
> URL: https://issues.apache.org/jira/browse/HDFS-5907
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode
> Affects Versions: HDFS-5535 (Rolling upgrades)
> Reporter: Arpit Agarwal
> Assignee: Arpit Agarwal
> Attachments: HDFS-5907.01.patch, HDFS-5907.02.patch
>
>
> DN changes when a rolling upgrade is in progress:
> # DataNode should handle block deletions by moving block files to 'trash'.
> # Block files should be restored to their original locations during a
> rollback.
> # Purge trash when the rolling upgrade is finalized.
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