[GitHub] [ozone] sodonnel commented on a diff in pull request #3519: HDDS-6891. Add CapacityVolumeChoosingPolicy

[GitBox <gi...@apache.org>]

sodonnel commented on code in PR #3519:
URL: https://github.com/apache/ozone/pull/3519#discussion_r899060680


##########
hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/CapacityVolumeChoosingPolicy.java:
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@@ -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.hadoop.ozone.container.common.volume;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.ozone.container.common.interfaces.VolumeChoosingPolicy;
+import org.apache.hadoop.util.DiskChecker.DiskOutOfSpaceException;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Random;
+import java.util.stream.Collectors;
+
+/**
+ * Volume choosing policy that randomly choose volume with remaining
+ * space to satisfy the size constraints.
+ * <p>
+ * The Algorithm is as follows, Pick 2 random volumes from a given pool of
+ * volumeSet and then pick the volume with lower utilization. This leads to a
+ * higher probability of volume with lower utilization to be picked.
+ * <p>
+ * Same algorithm as the SCMContainerPlacementCapacity.
+ */
+public class CapacityVolumeChoosingPolicy implements VolumeChoosingPolicy {
+
+  public static final Log LOG = LogFactory.getLog(
+      CapacityVolumeChoosingPolicy.class);
+
+  // Stores the index of the next volume to be returned.
+  private final Random random = new Random();
+
+  @Override
+  public HddsVolume chooseVolume(List<HddsVolume> volumes,
+      long maxContainerSize) throws IOException {
+
+    // No volumes available to choose from
+    if (volumes.size() < 1) {
+      throw new DiskOutOfSpaceException("No more available volumes");
+    }
+
+    List<HddsVolume> filtered = volumes.stream()
+        .filter(v ->
+            v.getAvailable() - v.getCommittedBytes() > maxContainerSize)
+        .collect(Collectors.toList());
+    if (filtered.size() < 1) {
+      throw new DiskOutOfSpaceException("Out of space: "
+          + "All volumes are less than the container size (=" + maxContainerSize
+          + " B).");
+    } else if (filtered.size() == 1) {
+      return filtered.get(0);
+    } else {
+      int firstIndex = random.nextInt(filtered.size());
+      int secondIndex = random.nextInt(filtered.size());

Review Comment:
   With a small number of volumes, there is a reasonable chance of selecting the same index twice here I think? We might need to do something to ensure you get two unique indexes.
   
   Also what about the case with only 2 volumes available? Do we always want to select the smallest one, or do we want to select the smaller one more often than the other? Maybe we need another if branch for 2 volumes available to handle it specially?



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