[HDFS-4937] ReplicationMonitor can infinite-loop in BlockPlacementPolicyDefault#chooseRandom()

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.0.4-alpha, 0.23.8
• Fix Version/s: 2.8.0, 2.7.3, 3.0.0-alpha1
• Component/s: namenode
• Labels: BB2015-05-TBR
• Target Version/s: 2.7.3
• Hadoop Flags: Reviewed
• Assignee: Kihwal Lee
• Reporter: Kihwal Lee
• Created: 25/Jun/13 21:44
• Updated: 10/Aug/18 14:39
• Resolved: 05/Nov/15 15:30

Description

When a large number of nodes are removed by refreshing node lists, the network topology is updated. If the refresh happens at the right moment, the replication monitor thread may stuck in the while loop of chooseRandom(). This is because the cached cluster size is used in the terminal condition check of the loop. This usually happens when a block with a high replication factor is being processed. Since replicas/rack is also calculated beforehand, no node choice may satisfy the goodness criteria if refreshing removed racks.

All nodes will end up in the excluded list, but the size will still be less than the cached cluster size, so it will loop infinitely. This was observed in a production environment.

Issue Links

• breaks: HDFS-9352 Test : Hadoop-HdfsTrunk test cases after HDFS-4937
• is superceded by: HDFS-10320 Rack failures may result in NN terminate
• relates to: HDFS-9287 Block placement completely fails if too many nodes are decommissioning