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https://issues.apache.org/jira/browse/HDFS-5709?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13877144#comment-13877144
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Aaron T. Myers commented on HDFS-5709:
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Hey guys,
Jing - I'm not in favor of a generic prefix for all reserved names because I
don't think it's flexible enough. A user should be able to rename a reserved
component name to a specific other reserved component name. With just a prefix
mutation, I could easily imagine having to run some operation after the NN had
started up to then find all of the renamed paths and again rename them to some
other name with the prefix removed. That's a pain that we shouldn't put our
users through.
Suresh - with regard to the suggestion that we have a completely generic system
of renaming reserved component names, how strongly do you see that as a
requirement? I personally view that as overkill for two reasons: 1) Empirically
we rarely add reserved names (only two in the lifetime of HDFS so far) and I
don't anticipate adding many more, and 2) we can't necessarily anticipate the
precise semantics of all reserved names. For example, ".reserved" should only
be considered invalid and renamed if it's in the root directory. I think the
solution for that is not to develop a completely generic system for renaming
path components, but rather to do as Andrew suggests and add a conf option per
reserved name, and add the code necessary for each one as it comes up.
I'm in favor of checking in this patch as-is. If we later decide to add a more
generic system, we can do that and quite easily maintain backward compatibility
of this conf option with that system. I wouldn't personally object to
implementing a K/V config setting system as Andrew suggested, but again, seems
like overkill to me.
> Improve upgrade with existing files and directories named ".snapshot"
> ---------------------------------------------------------------------
>
> Key: HDFS-5709
> URL: https://issues.apache.org/jira/browse/HDFS-5709
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Affects Versions: 3.0.0, 2.2.0
> Reporter: Andrew Wang
> Assignee: Andrew Wang
> Labels: snapshots, upgrade
> Attachments: hdfs-5709-1.patch, hdfs-5709-2.patch, hdfs-5709-3.patch,
> hdfs-5709-4.patch, hdfs-5709-5.patch
>
>
> Right now in trunk, upgrade fails messily if the old fsimage or edits refer
> to a directory named ".snapshot". We should at least print a better error
> message (which I believe was the original intention in HDFS-4666), and [~atm]
> proposed automatically renaming these files and directories.
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