[HDFS-1590] Decommissioning never ends when node to decommission has blocks that are under-replicated and cannot be replicated to the expected level of replication

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 0.20.2
• Component/s: namenode

Environment

Linux

• Assignee: Unassigned
• Reporter: Mathias Herberts
• Created: 21/Jan/11 15:58
• Updated: 06/Dec/18 09:58

Description

On a test cluster with 4 DNs and a default repl level of 3, I recently attempted to decommission one of the DNs. Right after the modification of the dfs.hosts.exclude file and the 'dfsadmin -refreshNodes', I could see the blocks being replicated to other nodes.

After a while, the replication stopped but the node was not marked as decommissioned.

When running an 'fsck -files -blocks -locations' I saw that all files had a replication of 4 (which is logical given there are 4 DNs), but some of the files had an expected replication set to 10 (those were job.jar files from M/R jobs).

I ran 'fs -setrep 3' on those files and shortly after the namenode reported the DN as decommissioned.

Shouldn't this case be checked by the NameNode when decommissioning a node? I.e considere a node decommissioned if either one of the following is true for each block on the node being decommissioned:

1. It is replicated more than the expected replication level.
2. It is replicated as much as possible given the available nodes, even though it is less replicated than expected.