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Subject [GitHub] StefanRRichter commented on a change in pull request #6898: [FLINK-10431] Extraction of scheduling-related code from SlotPool into preliminary Scheduler
Date Tue, 23 Oct 2018 16:18:39 GMT
StefanRRichter commented on a change in pull request #6898: [FLINK-10431] Extraction of scheduling-related
code from SlotPool into preliminary Scheduler
URL: https://github.com/apache/flink/pull/6898#discussion_r227466414
 
 

 ##########
 File path: flink-runtime/src/main/java/org/apache/flink/runtime/jobmaster/slotpool/PreviousAllocationSlotSelectionStrategy.java
 ##########
 @@ -0,0 +1,82 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.runtime.jobmaster.slotpool;
+
+import org.apache.flink.runtime.clusterframework.types.AllocationID;
+import org.apache.flink.runtime.clusterframework.types.SlotProfile;
+import org.apache.flink.runtime.jobmanager.scheduler.Locality;
+import org.apache.flink.runtime.jobmaster.SlotInfo;
+
+import javax.annotation.Nonnull;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * This class implements a {@link SlotSelectionStrategy} that is based on previous allocations
and
+ * falls back to using location preference hints if there is no previous allocation.
+ */
+public class PreviousAllocationSlotSelectionStrategy implements SlotSelectionStrategy {
+
+	public static final PreviousAllocationSlotSelectionStrategy INSTANCE =
+		new PreviousAllocationSlotSelectionStrategy();
+
+	private final LocationPreferenceSlotSelection locationPreferenceSlotSelection;
+
+	private PreviousAllocationSlotSelectionStrategy() {
+		this.locationPreferenceSlotSelection = LocationPreferenceSlotSelection.INSTANCE;
+	}
+
+	@Nonnull
+	@Override
+	public SlotInfoAndLocality selectBestSlotForProfile(
+		@Nonnull List<SlotInfo> availableSlots,
+		@Nonnull SlotProfile slotProfile) {
+
+		Collection<AllocationID> priorAllocations = slotProfile.getPreferredAllocations();
+
+		// First, if there was a prior allocation try to schedule to the same/old slot
+		if (!priorAllocations.isEmpty()) {
+
+			HashSet<AllocationID> priorAllocationsSet = new HashSet<>(priorAllocations);
 
 Review comment:
   In theory: it is a collection and contains on a collection can be expensive, depending
on the implementation. A hash set offers ideal performance for contains.
   In practise, this collections is currently always of size 1, so either way, it should not
matter much. But as the code could evolve, I prefer not to create a potential complexity bomb
:)

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