Class PreemptionMessage

  extended by org.apache.hadoop.yarn.api.records.PreemptionMessage

public abstract class PreemptionMessage
extends Object

A PreemptionMessage is part of the RM-AM protocol, and it is used by the RM to specify resources that the RM wants to reclaim from this ApplicationMaster (AM). The AM receives a StrictPreemptionContract message encoding which containers the platform may forcibly kill, granting it an opportunity to checkpoint state or adjust its execution plan. The message may also include a PreemptionContract granting the AM more latitude in selecting which resources to return to the cluster.

The AM should decode both parts of the message. The StrictPreemptionContract specifies particular allocations that the RM requires back. The AM can checkpoint containers' state, adjust its execution plan to move the computation, or take no action and hope that conditions that caused the RM to ask for the container will change.

In contrast, the PreemptionContract also includes a description of resources with a set of containers. If the AM releases containers matching that profile, then the containers enumerated in PreemptionContract.getContainers() may not be killed.

Each preemption message reflects the RM's current understanding of the cluster state, so a request to return N containers may not reflect containers the AM is releasing, recently exited containers the RM has yet to learn about, or new containers allocated before the message was generated. Conversely, an RM may request a different profile of containers in subsequent requests.

The policy enforced by the RM is part of the scheduler. Generally, only containers that have been requested consistently should be killed, but the details are not specified.

Constructor Summary
Method Summary
abstract  PreemptionContract getContract()
abstract  StrictPreemptionContract getStrictContract()
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail


public PreemptionMessage()
Method Detail


public abstract StrictPreemptionContract getStrictContract()
Specific resources that may be killed by the ResourceManager


public abstract PreemptionContract getContract()
Contract describing resources to return to the cluster.

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