[HDFS-4702] remove namesystem lock from DatanodeManager#fetchDatanodes

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Duplicate
• Affects Version/s: 3.0.0-alpha1
• Component/s: namenode
• Assignee: Chris Nauroth
• Reporter: Chris Nauroth
• Created: 16/Apr/13 03:05
• Updated: 15/May/18 22:53
• Resolved: 15/May/18 22:53

Description

DatanodeManager#fetchDatanodes currently holds the namesystem read lock while iterating through data nodes. This method is called from the namenode web UI. HDFS-3990 reported a performance problem in this code path. This is a follow-up jira to investigate whether or not we can remove the lock.

Issue Links

• is related to: HDFS-2206 Add read-write lock to DatanodeManager
• is related to: HDFS-3990 NN's health report has severe performance problems
• is related to: HDFS-4269 DatanodeManager#registerDatanode rejects all datanode registrations from localhost in single-node developer setup
• is related to: HADOOP-1762 Namenode does not need to store storageID and datanodeID persistently
• is related to: HDFS-3137 Bump LAST_UPGRADABLE_LAYOUT_VERSION to -16