[HDFS-16450] Give priority to releasing DNs with less free space

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.3.0
• Component/s: hdfs
• Assignee: yanbin.zhang
• Reporter: yanbin.zhang
• Created: 09/Feb/22 10:14
• Updated: 14/Apr/22 02:47

Description

When deleting redundant replicas, the one with the least free space should be prioritized.

//BlockPlacementPolicyDefault#chooseReplicaToDelete
final DatanodeStorageInfo storage;
if (oldestHeartbeatStorage != null) {
  storage = oldestHeartbeatStorage;
} else if (minSpaceStorage != null) {
  storage = minSpaceStorage;
} else {
  return null;
}
excessTypes.remove(storage.getStorageType());
return storage; 

Change the above logic to the following:

//BlockPlacementPolicyDefault#chooseReplicaToDelete
final DatanodeStorageInfo storage;
if (minSpaceStorage != null) {
  storage = minSpaceStorage;
} else if (oldestHeartbeatStorage != null) {
  storage = oldestHeartbeatStorage;
} else {
  return null;
}