Ngone51 opened a new pull request #23377: [SPARK-26439][CORE][WIP] Introduce WorkerOffer reservation mechanism for Barrier TaskSet URL: https://github.com/apache/spark/pull/23377 ## What changes were proposed in this pull request? Currently, Barrier TaskSet has a hard requirement that tasks can only be launched in a single resourceOffers round with enough slots(or sufficient resources), but can not be guaranteed even if with enough slots due to task locality delay scheduling. So, it is very likely that Barrier TaskSet gets a chunk of sufficient resources after all the trouble, but let it go easily just beacuae one of pending tasks can not be scheduled. Futhermore, it causes severe resource competition between TaskSets and jobs and introduce unclear semantic for DynamicAllocation. This pr trys to introduce WorkOffer reservation mechanism for Barrier TaskSet, which allows Barrier TaskSet to reserve WorkOffer in each resourceOffers round, and launch tasks at the same time once it accumulate the sufficient resource. In this way, we relax the requirement of resources for the Barrier TaskSet. To avoid the deadlock which may be introuduced by serveral Barrier TaskSets holding the reserved WorkOffer for a long time, we'll ask Barrier TaskSets to force releasing part of reserved WorkOffers on demand. So, it is highly possible that each Barrier TaskSet would be launched in the end. To integrate with DynamicAllocation: The possible effective way I can imagine is that adding new event, e.g. ExecutorReservedEvent, ExecutorReleasedEvent, which behaved like busy executor with running tasks or idle executor without running tasks. Thus, ExecutionAllocationManager would not let the executor go if it reminds of there're some reserved resource on that executor. ## How was this patch tested? existed and added one yet, needs to add more.
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