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https://issues.apache.org/jira/browse/HDFS-14527?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16856309#comment-16856309
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He Xiaoqiao commented on HDFS-14527:
------------------------------------
[^HDFS-14527.005.patch] fix checkstyle and rename {{chooseTargetFuturn}} to
{{chooseTargetFuture}}.
check the failed unit test, It seems not relate with this issue.
> Stop all DataNodes may result in NN terminate
> ---------------------------------------------
>
> Key: HDFS-14527
> URL: https://issues.apache.org/jira/browse/HDFS-14527
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Reporter: He Xiaoqiao
> Assignee: He Xiaoqiao
> Priority: Major
> Attachments: HDFS-14527.001.patch, HDFS-14527.002.patch,
> HDFS-14527.003.patch, HDFS-14527.004.patch, HDFS-14527.005.patch
>
>
> If we stop all datanodes of cluster, BlockPlacementPolicyDefault#chooseTarget
> may get ArithmeticException when calling #getMaxNodesPerRack, which throws
> the runtime exception out to BlockManager's ReplicationMonitor thread and
> then terminate the NN.
> The root cause is that BlockPlacementPolicyDefault#chooseTarget not hold the
> global lock, and if all DataNodes are dead between
> {{clusterMap.getNumberOfLeaves()}} and {{getMaxNodesPerRack}} then it meet
> {{ArithmeticException}} while invoke {{getMaxNodesPerRack}}.
> {code:java}
> private DatanodeStorageInfo[] chooseTarget(int numOfReplicas,
> Node writer,
> List<DatanodeStorageInfo> chosenStorage,
> boolean returnChosenNodes,
> Set<Node> excludedNodes,
> long blocksize,
> final BlockStoragePolicy storagePolicy,
> EnumSet<AddBlockFlag> addBlockFlags,
> EnumMap<StorageType, Integer> sTypes) {
> if (numOfReplicas == 0 || clusterMap.getNumOfLeaves()==0) {
> return DatanodeStorageInfo.EMPTY_ARRAY;
> }
> ......
> int[] result = getMaxNodesPerRack(chosenStorage.size(), numOfReplicas);
> ......
> }
> {code}
> Some detailed log show as following.
> {code:java}
> 2019-05-31 12:29:21,803 ERROR
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager:
> ReplicationMonitor thread received Runtime exception.
> java.lang.ArithmeticException: / by zero
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.getMaxNodesPerRack(BlockPlacementPolicyDefault.java:282)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:228)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:132)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$ReplicationWork.chooseTargets(BlockManager.java:4533)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$ReplicationWork.access$1800(BlockManager.java:4493)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReplicationWorkForBlocks(BlockManager.java:1954)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReplicationWork(BlockManager.java:1830)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeDatanodeWork(BlockManager.java:4453)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$ReplicationMonitor.run(BlockManager.java:4388)
> at java.lang.Thread.run(Thread.java:745)
> 2019-05-31 12:29:21,805 INFO org.apache.hadoop.util.ExitUtil: Exiting with
> status 1
> {code}
> To be honest, this is not serious bug and not reprod easily, since if we stop
> all Datanodes and only keep NameNode lives, HDFS could be not offer service
> normally and we could only retrieve directory. It may be one corner case.
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