[HDFS-12137] DN dataset lock should be fair

• Type: Improvement
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 2.8.0
• Fix Version/s: 2.9.0, 3.0.0-beta1, 2.8.2
• Component/s: datanode
• Target Version/s: 2.8.2
• Hadoop Flags: Reviewed
• Assignee: Daryn Sharp
• Reporter: Daryn Sharp
• Created: 13/Jul/17 19:55
• Updated: 25/Jul/17 04:43
• Resolved: 14/Jul/17 20:55

Description

The dataset lock is very highly contended. The unfair nature can be especially harmful to the heartbeat handling. Under high loads, partially expose by HDFS-12136 introducing disk i/o within the lock, the heartbeat handling thread may process commands so slowly due to the contention that the node becomes stale or falsely declared dead. The unfair lock is not helping and appears to be causing frequent starvation under load.