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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9837) BlockManager#countNodes should be able to detect duplicated internal blocks
Date Tue, 23 Feb 2016 21:29:18 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9837?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15159673#comment-15159673
] 

Tsz Wo Nicholas Sze commented on HDFS-9837:
-------------------------------------------

> Thanks Jing Zhao for the work. EnumCounters<StoredReplicaState> idea looks pretty
good. ...

Agree. Using EnumCounters is great.  Thanks Jing.

Some more comment on the patch:

- NumberReplicas may extend EnumCounters<StoredReplicaState> instead of having a counters
field.  Then, we don't need the local EnumCounters<StoredReplicaState> variable  in
other methods.

- numReplicas in chooseSourceDatanodes(..) is never null so that we may remove the null check.
 We may use it directly and remove the local counters variable.

- checkReplicaOnStorage may return StoredReplicaState for LIVE, CORRUPT, EXCESS, DECOMMISSIONING,
DECOMMISSIONED or READONLY but ignoring STALESTORAGE.  Then, we don't need to re-compute isCorrupt
and isExcess outside the method.


> BlockManager#countNodes should be able to detect duplicated internal blocks
> ---------------------------------------------------------------------------
>
>                 Key: HDFS-9837
>                 URL: https://issues.apache.org/jira/browse/HDFS-9837
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>    Affects Versions: 3.0.0
>            Reporter: Jing Zhao
>            Assignee: Jing Zhao
>         Attachments: HDFS-9837.000.patch, HDFS-9837.001.patch, HDFS-9837.002.patch, HDFS-9837.003.patch
>
>
> Currently {{BlockManager#countNodes}} only counts the number of replicas/internal blocks
thus it cannot detect the under-replicated scenario where a striped EC block has 9 internal
blocks but contains duplicated data/parity blocks. E.g., b8 is missing while 2 b0 exist:
> b0, b1, b2, b3, b4, b5, b6, b7, b0
> If the NameNode keeps running, NN is able to detect the duplication of b0 and will put
the block into the excess map. {{countNodes}} excludes internal blocks captured in the excess
map thus can return the correct number of live replicas. However, if NN restarts before sending
out the reconstruction command, the missing internal block cannot be detected anymore. The
following steps can reproduce the issue:
> # create an EC file
> # kill DN1 and wait for the reconstruction to happen
> # start DN1 again
> # kill DN2 and restart NN immediately



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