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https://issues.apache.org/jira/browse/HDFS-4015?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14945939#comment-14945939
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Arpit Agarwal commented on HDFS-4015:
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Hi [~anu], thanks for addressing the earlier feedback. Feedback on the v2 patch.
# We will likely see blocks with future generation stamps during HDFS rollback.
We should disable this check if NN has been restarted with a rollback option
(either regular or rolling upgrade rollback).
# I apologize for not noticing this earlier. {{FsStatus}} is tagged as public
and stable, so changing the constructor signature is incompatible. Instead we
could add a new constructor that initializes . This will also avoid changes to
FileSystem, ViewFS, RawLocalFileSystem
# fsck should also print this new counter. We can do it in a separate Jira.
# Don't consider this a binding but I would really like it if {{bytesInFuture}}
can be renamed especially where it is exposed via public interfaces/metrics. It
sounds confusing/ominous. {{bytesWithFutureGenerationStamps}} would be more
precise.
Still reviewing the test cases.
> Safemode should count and report orphaned blocks
> ------------------------------------------------
>
> Key: HDFS-4015
> URL: https://issues.apache.org/jira/browse/HDFS-4015
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Affects Versions: 3.0.0
> Reporter: Todd Lipcon
> Assignee: Anu Engineer
> Attachments: HDFS-4015.001.patch, HDFS-4015.002.patch
>
>
> The safemode status currently reports the number of unique reported blocks
> compared to the total number of blocks referenced by the namespace. However,
> it does not report the inverse: blocks which are reported by datanodes but
> not referenced by the namespace.
> In the case that an admin accidentally starts up from an old image, this can
> be confusing: safemode and fsck will show "corrupt files", which are the
> files which actually have been deleted but got resurrected by restarting from
> the old image. This will convince them that they can safely force leave
> safemode and remove these files -- after all, they know that those files
> should really have been deleted. However, they're not aware that leaving
> safemode will also unrecoverably delete a bunch of other block files which
> have been orphaned due to the namespace rollback.
> I'd like to consider reporting something like: "900000 of expected 1000000
> blocks have been reported. Additionally, 10000 blocks have been reported
> which do not correspond to any file in the namespace. Forcing exit of
> safemode will unrecoverably remove those data blocks"
> Whether this statistic is also used for some kind of "inverse safe mode" is
> the logical next step, but just reporting it as a warning seems easy enough
> to accomplish and worth doing.
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