[HDFS-2825] Add test hook to turn off the writer preferring its local DN

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.23.0
• Fix Version/s: 0.23.1
• Component/s: namenode
• Target Version/s: 0.23.1
• Hadoop Flags: Reviewed
• Assignee: Todd Lipcon
• Reporter: Todd Lipcon
• Created: 23/Jan/12 02:39
• Updated: 10/Mar/15 02:04
• Resolved: 23/Jan/12 22:08

Description

Currently, the default block placement policy always places the first replica in the pipeline on the local node if there is a valid DN running there. In some network designs, within-rack bandwidth is never constrained so this doesn't give much of an advantage. It would also be really useful to disable this for MiniDFSCluster tests, since currently if you start a multi-DN cluster and write with replication level 1, all of the replicas go to the same DN.
[per discussion below, this was changed to not add a config, but only to add a hook for testing]

Issue Links

• blocks: HDFS-2826 Test case for HDFS-1476 (safemode can initialize repl queues before exiting)