DecommissioningNodesWatcher (Apache Hadoop YARN ResourceManager 2.10.2 API)

```
public class DecommissioningNodesWatcher
extends Object
```
DecommissioningNodesWatcher is used by ResourceTrackerService to track DECOMMISSIONING nodes to decide when, after all running containers on the node have completed, will be transitioned into DECOMMISSIONED state (NodeManager will be told to shutdown). Under MR application, a node, after completes all its containers, may still serve it map output data during the duration of the application for reducers. A fully graceful mechanism would keep such DECOMMISSIONING nodes until all involved applications complete. It could be however undesirable under long-running applications scenario where a bunch of "idle" nodes would stay around for long period of time. DecommissioningNodesWatcher balance such concern with a timeout policy --- a DECOMMISSIONING node will be DECOMMISSIONED no later than DECOMMISSIONING_TIMEOUT regardless of running containers or applications. To be efficient, DecommissioningNodesWatcher skip tracking application containers on a particular node before the node is in DECOMMISSIONING state. It only tracks containers once the node is in DECOMMISSIONING state. DecommissioningNodesWatcher basically is no cost when no node is DECOMMISSIONING. This sacrifices the possibility that the node once host containers of an application that is still running (the affected map tasks will be rescheduled).

Nested Classes
Modifier and Type	Class and Description
`static class`	`DecommissioningNodesWatcher.DecommissioningNodeStatus` Status about a specific decommissioning node.

Constructors
Constructor and Description
`DecommissioningNodesWatcher(RMContext rmContext)`

Methods
Modifier and Type	Method and Description
`DecommissioningNodesWatcher.DecommissioningNodeStatus`	`checkDecommissioningStatus(org.apache.hadoop.yarn.api.records.NodeId nodeId)`
`boolean`	`checkReadyToBeDecommissioned(org.apache.hadoop.yarn.api.records.NodeId nodeId)`
`void`	`init(org.apache.hadoop.conf.Configuration conf)`
`void`	`remove(org.apache.hadoop.yarn.api.records.NodeId nodeId)`
`void`	`update(RMNode rmNode, org.apache.hadoop.yarn.server.api.records.NodeStatus remoteNodeStatus)` Update rmNode decommissioning status based on NodeStatus.

public DecommissioningNodesWatcher(RMContext rmContext)

public void init(org.apache.hadoop.conf.Configuration conf)

public void remove(org.apache.hadoop.yarn.api.records.NodeId nodeId)

public boolean checkReadyToBeDecommissioned(org.apache.hadoop.yarn.api.records.NodeId nodeId)

public DecommissioningNodesWatcher.DecommissioningNodeStatus checkDecommissioningStatus(org.apache.hadoop.yarn.api.records.NodeId nodeId)

Class DecommissioningNodesWatcher