Github user squito commented on a diff in the pull request: https://github.com/apache/spark/pull/15221#discussion_r80312510 --- Diff: core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala --- @@ -216,7 +216,7 @@ class CoarseGrainedSchedulerBackend(scheduler: TaskSchedulerImpl, val rpcEnv: Rp val activeExecutors = executorDataMap.filterKeys(executorIsAlive) val workOffers = activeExecutors.map { case (id, executorData) => new WorkerOffer(id, executorData.executorHost, executorData.freeCores) - }.toSeq + }.toIndexedSeq --- End diff -- this just happened to generate an `IndexedSeq` before in any case, which is why this wasn't a performance bottleneck. But if scala libs and decided to generate something else on the call to `.toSeq`, scheduling performance would tank before this change.
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