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https://issues.apache.org/jira/browse/HDFS-12638?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16245134#comment-16245134
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Konstantin Shvachko commented on HDFS-12638:
--------------------------------------------
[~wweic] {{addDeleteBlock()}} is supposed to be called, when the block is
really intended to be deleted, that is it is not contained in any snapshots. I
checked the code, there is a lot of logic around detecting which blocks belong
or not to a snapshot, see e.g. {{INodeFile.collectBlocksBeyondSnapshot()}}.
This makes it safe to delete the {{truncateBlock}}. Unless you have a test case
as a counterexample.
Did some digging and now understand why we don't see this in 2.7.4. The
following line was introduced into {{addDeleteBlock()}} by HDFS-9754:
{code}
assert toDelete != null : "toDelete is null";
+ toDelete.delete();
toDeleteList.add(toDelete);
{code}
which sets {{Block.bcId = INVALID_INODE_ID}}. I think this was the wrong place
to invalidate bcId, as [I mensioned
earlier|https://issues.apache.org/jira/browse/HDFS-12638?focusedCommentId=16214120&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-16214120].
[~jingzhao] could you please take a look.
> NameNode exits due to ReplicationMonitor thread received Runtime exception in
> ReplicationWork#chooseTargets
> -----------------------------------------------------------------------------------------------------------
>
> Key: HDFS-12638
> URL: https://issues.apache.org/jira/browse/HDFS-12638
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs
> Affects Versions: 2.8.2
> Reporter: Jiandan Yang
> Attachments: HDFS-12638-branch-2.8.2.001.patch, HDFS-12638.002.patch,
> OphanBlocksAfterTruncateDelete.jpg
>
>
> Active NamNode exit due to NPE, I can confirm that the BlockCollection passed
> in when creating ReplicationWork is null, but I do not know why
> BlockCollection is null, By view history I found
> [HDFS-9754|https://issues.apache.org/jira/browse/HDFS-9754] remove judging
> whether BlockCollection is null.
> NN logs are as following:
> {code:java}
> 2017-10-11 16:29:06,161 ERROR [ReplicationMonitor]
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager:
> ReplicationMonitor thread received Runtime exception.
> java.lang.NullPointerException
> at
> org.apache.hadoop.hdfs.server.blockmanagement.ReplicationWork.chooseTargets(ReplicationWork.java:55)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReplicationWorkForBlocks(BlockManager.java:1532)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReplicationWork(BlockManager.java:1491)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeDatanodeWork(BlockManager.java:3792)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$ReplicationMonitor.run(BlockManager.java:3744)
> at java.lang.Thread.run(Thread.java:834)
> {code}
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