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https://issues.apache.org/jira/browse/HDFS-10453?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16359229#comment-16359229
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Arpit Agarwal commented on HDFS-10453:
--------------------------------------

+1 for HDFS-10453-trunk.002.patch, pending Jenkins.

> ReplicationMonitor thread could stuck for long time due to the race between 
> replication and delete of same file in a large cluster.
> -----------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-10453
>                 URL: https://issues.apache.org/jira/browse/HDFS-10453
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.4.1, 2.5.2, 2.7.1, 2.6.4
>            Reporter: He Xiaoqiao
>            Assignee: He Xiaoqiao
>            Priority: Major
>             Fix For: 2.7.6
>
>         Attachments: HDFS-10453-branch-2.001.patch, 
> HDFS-10453-branch-2.003.patch, HDFS-10453-branch-2.7.004.patch, 
> HDFS-10453-branch-2.7.005.patch, HDFS-10453-branch-2.7.006.patch, 
> HDFS-10453-branch-2.7.007.patch, HDFS-10453-branch-2.7.008.patch, 
> HDFS-10453-branch-2.7.009.patch, HDFS-10453-branch-2.8.001.patch, 
> HDFS-10453-branch-2.8.002.patch, HDFS-10453-branch-2.9.001.patch, 
> HDFS-10453-branch-2.9.002.patch, HDFS-10453-branch-3.0.001.patch, 
> HDFS-10453-branch-3.0.002.patch, HDFS-10453-trunk.001.patch, 
> HDFS-10453-trunk.002.patch, HDFS-10453.001.patch
>
>
> ReplicationMonitor thread could stuck for long time and loss data with little 
> probability. Consider the typical scenarioļ¼š
> (1) create and close a file with the default replicas(3);
> (2) increase replication (to 10) of the file.
> (3) delete the file while ReplicationMonitor is scheduling blocks belong to 
> that file for replications.
> if ReplicationMonitor stuck reappeared, NameNode will print log as:
> {code:xml}
> 2016-04-19 10:20:48,083 WARN 
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy: Failed to 
> place enough replicas, still in need of 7 to reach 10 
> (unavailableStorages=[], storagePolicy=BlockStoragePolicy{HOT:7, 
> storageTypes=[DISK], creationFallbacks=[], replicationFallbacks=[ARCHIVE]}, 
> newBlock=false) For more information, please enable DEBUG log level on 
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy
> ......
> 2016-04-19 10:21:17,184 WARN 
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy: Failed to 
> place enough replicas, still in need of 7 to reach 10 
> (unavailableStorages=[DISK], storagePolicy=BlockStoragePolicy{HOT:7, 
> storageTypes=[DISK], creationFallbacks=[], replicationFallbacks=[ARCHIVE]}, 
> newBlock=false) For more information, please enable DEBUG log level on 
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy
> 2016-04-19 10:21:17,184 WARN 
> org.apache.hadoop.hdfs.protocol.BlockStoragePolicy: Failed to place enough 
> replicas: expected size is 7 but only 0 storage types can be selected 
> (replication=10, selected=[], unavailable=[DISK, ARCHIVE], removed=[DISK, 
> DISK, DISK, DISK, DISK, DISK, DISK], policy=BlockStoragePolicy{HOT:7, 
> storageTypes=[DISK], creationFallbacks=[], replicationFallbacks=[ARCHIVE]})
> 2016-04-19 10:21:17,184 WARN 
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy: Failed to 
> place enough replicas, still in need of 7 to reach 10 
> (unavailableStorages=[DISK, ARCHIVE], storagePolicy=BlockStoragePolicy{HOT:7, 
> storageTypes=[DISK], creationFallbacks=[], replicationFallbacks=[ARCHIVE]}, 
> newBlock=false) All required storage types are unavailable:  
> unavailableStorages=[DISK, ARCHIVE], storagePolicy=BlockStoragePolicy{HOT:7, 
> storageTypes=[DISK], creationFallbacks=[], replicationFallbacks=[ARCHIVE]}
> {code}
> This is because 2 threads (#NameNodeRpcServer and #ReplicationMonitor) 
> process same block at the same moment.
> (1) ReplicationMonitor#computeReplicationWorkForBlocks get blocks to 
> replicate and leave the global lock.
> (2) FSNamesystem#delete invoked to delete blocks then clear the reference in 
> blocksmap, needReplications, etc. the block's NumBytes will set 
> NO_ACK(Long.MAX_VALUE) which is used to indicate that the block deletion does 
> not need explicit ACK from the node. 
> (3) ReplicationMonitor#computeReplicationWorkForBlocks continue to 
> chooseTargets for the same blocks and no node will be selected after traverse 
> whole cluster because  no node choice satisfy the goodness criteria 
> (remaining spaces achieve required size Long.MAX_VALUE). 
> During of stage#3 ReplicationMonitor stuck for long time, especial in a large 
> cluster. invalidateBlocks & neededReplications continues to grow and no 
> consumes. it will loss data at the worst.
> This can mostly be avoided by skip chooseTarget for BlockCommand.NO_ACK block 
> and remove it from neededReplications.



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