[HDFS-15495] Decommissioning a DataNode with corrupted EC files should not be blocked indefinitely

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.0.0
• Component/s: block placement, ec
• Assignee: Siyao Meng
• Reporter: Siyao Meng
• Created: 27/Jul/20 23:46
• Updated: 29/Jul/20 22:20

Description

Originally discovered in patched CDH 6.2.1 (with a bunch of EC fixes: HDFS-14699, HDFS-14849, HDFS-14847, HDFS-14920, HDFS-14768, HDFS-14946, HDFS-15186).

When there's an EC file marked as corrupted on NN, if the admin tries to decommission a DataNode having one of the remaining blocks of the corrupted EC file, the decom will never finish unless the file is recovered by putting the missing blocks back in:

The endless DatanodeAdminManager check loop, every 30s

2020-07-23 16:36:12,805 TRACE blockmanagement.DatanodeAdminManager: Processed 0 blocks so far this tick
2020-07-23 16:36:12,806 DEBUG blockmanagement.DatanodeAdminManager: Processing Decommission In Progress node 127.0.1.7:5007
2020-07-23 16:36:12,806 TRACE blockmanagement.DatanodeAdminManager: Block blk_-9223372036854775728_1013 numExpected=9, numLive=4
2020-07-23 16:36:12,806 INFO BlockStateChange: Block: blk_-9223372036854775728_1013, Expected Replicas: 9, live replicas: 4, corrupt replicas: 0, decommissioned replicas: 0, decommissioning replicas: 1, maintenance replicas: 0, live entering maintenance replicas: 0, excess replicas: 0, Is Open File: false, Datanodes having this block: 127.0.1.12:5012 127.0.1.10:5010 127.0.1.8:5008 127.0.1.11:5011 127.0.1.7:5007 , Current Datanode: 127.0.1.7:5007, Is current datanode decommissioning: true, Is current datanode entering maintenance: false
2020-07-23 16:36:12,806 DEBUG blockmanagement.DatanodeAdminManager: Node 127.0.1.7:5007 still has 1 blocks to replicate before it is a candidate to finish Decommission In Progress.
2020-07-23 16:36:12,806 INFO blockmanagement.DatanodeAdminManager: Checked 1 blocks and 1 nodes this tick

"Corrupted" file here meaning the EC file doesn't have enough EC blocks in the block group to be reconstructed. e.g. for RS-6-3-1024k, when there are less than 6 blocks for an EC file, the file can no longer be retrieved correctly.