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From "Harsh J (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-9949) Testcase for catching DN UUID regeneration regression
Date Sun, 13 Mar 2016 02:11:34 GMT

     [ https://issues.apache.org/jira/browse/HDFS-9949?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Harsh J updated HDFS-9949:
--------------------------
    Attachment: HDFS-9949.000.branch-2.7.not-for-commit.patch
                HDFS-9949.000.patch

> Testcase for catching DN UUID regeneration regression
> -----------------------------------------------------
>
>                 Key: HDFS-9949
>                 URL: https://issues.apache.org/jira/browse/HDFS-9949
>             Project: Hadoop HDFS
>          Issue Type: Test
>    Affects Versions: 2.6.0
>            Reporter: Harsh J
>            Assignee: Harsh J
>            Priority: Minor
>         Attachments: HDFS-9949.000.branch-2.7.not-for-commit.patch, HDFS-9949.000.patch
>
>
> In the following scenario, in releases without HDFS-8211, the DN may regenerate its UUIDs
unintentionally.
> 0. Consider a DN with two disks {{/data1/dfs/dn,/data2/dfs/dn}}
> 1. Stop DN
> 2. Unmount the second disk, {{/data2/dfs/dn}}
> 3. Create (in the scenario, this was an accident) /data2/dfs/dn on the root path
> 4. Start DN
> 5. DN now considers /data2/dfs/dn empty so formats it, but during the format it uses
{{datanode.getDatanodeUuid()}} which is null until register() is called.
> 6. As a result, after the directory loading, {{datanode.checkDatanodUuid()}} gets called
with successful condition, and it causes a new generation of UUID which is written to all
disks {{/data1/dfs/dn/current/VERSION}} and {{/data2/dfs/dn/current/VERSION}}.
> 7. Stop DN (in the scenario, this was when the mistake of unmounted disk was realised)
> 8. Mount the second disk back again {{/data2/dfs/dn}}, causing the {{VERSION}} file to
be the original one again on it (mounting masks the root path that we last generated upon).
> 9. DN fails to start up cause it finds mismatched UUID between the two disks
> The DN should not generate a new UUID if one of the storage disks already have the older
one.
> HDFS-8211 unintentionally fixes this by changing the {{datanode.getDatanodeUuid()}} function
to rely on the {{DataStorage}} representation of the UUID vs. the {{DatanodeID}} object which
only gets available (non-null) _after_ the registration.
> It'd still be good to add a direct test case to the above scenario that passes on trunk
and branch-2, but fails on branch-2.7 and lower, so we can catch a regression around this
in future.



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