[HDFS-8860] Remove unused Replica copyOnWrite code

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.8.0, 3.0.0-alpha1
• Fix Version/s: 2.8.0, 3.0.0-alpha1
• Target Version/s: 2.8.0
• Assignee: Lei (Eddy) Xu
• Reporter: Lei (Eddy) Xu
• Created: 05/Aug/15 22:44
• Updated: 30/Aug/16 01:30
• Resolved: 14/Dec/15 23:35

Description

ReplicaInfo#unlinkBlock() is effectively disabled by the following code, because isUnlinked() always returns true.

if (isUnlinked()) {
  return false;
}

Several test cases, e.g., TestFileAppend#testCopyOnWrite and TestDatanodeRestart#testRecoverReplicas are testing against the unlink
Lets remove the relevant code to eliminate the confusions.

Issue Links

• breaks: HDFS-9589 Block files which have been hardlinked should be duplicated before the DataNode appends to the them
• is related to: HADOOP-2655 Copy on write for data and metadata files in the presence of snapshots