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https://issues.apache.org/jira/browse/HDFS-5709?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13861835#comment-13861835
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Suresh Srinivas commented on HDFS-5709:
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bq. Hey Suresh, could you elaborate a bit on your -1?
Sorry I should have added more details in my previous comment. Silently
renaming it will cause issues to any applications that depend on the name
.snapshot. I would rather make it an active decision during upgrade so that the
admin can take care of renaming to appropriate name he chooses and also ensure
applications that depend on such naming are updated. Otherwise upgrade will
silently succeed followed by failures.
I am assuming that .snapshot is used in very few clusters. In such a case cost
of rollback and rename probably should not affect large number of clusters.
As regards to tool to run for pre-upgrade, there are several issues:
# This tool can be available only in later releases (as we cannot change older
releases already installed on the cluster).
# A user may not run the tool, even if it is made available on newer release
and will have to rollback (as you pointed out)
# The pre-upgrade tool must consume fsimage and editlog (even if there is no
.snapshot file/directory). This will extend the time for upgrade for every
upgrade.
One possible solution is to turn of snapshot feature post upgade and allow
.snapshot directory or file. When a user tries to turn on .snapshot the
namenode fails to come up, forcing them to turn off the feature, rename
directories and turn it back on again. This may be a lot of work.
> 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
> Labels: snapshots, upgrade
>
> 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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