[HDFS-6701] Make seed optional in NetworkTopology#sortByDistance

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.5.0
• Fix Version/s: 2.6.0
• Component/s: namenode
• Target Version/s: 2.6.0
• Assignee: Ashwin Shankar
• Reporter: Ashwin Shankar
• Created: 18/Jul/14 02:51
• Updated: 01/Dec/14 03:08
• Resolved: 22/Jul/14 17:50

Description

Currently seed in NetworkTopology#sortByDistance is set to the blockid which causes the RNG to generate same pseudo random order for each block. If no node local block location is present,this causes the same rack local replica to be hit for a particular block.
It'll be good to make the seed optional, so that one could turn it off if they want block locations of a block to be randomized.

Issue Links

• is related to: HDFS-6840 Clients are always sent to the same datanode when read is off rack