He Xiaoqiao created HDFS-10453:
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Summary: 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: 2.7.1
Reporter: He Xiaoqiao
ReplicationMonitor thread could stuck for long time and loss data with little
probability. Consider the typical scenarioļ¼
(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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