[GitHub] [ozone] symious commented on a change in pull request #2497: HDDS-5326. EC: Create a new as many racks as possible placement policy for EC

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

symious commented on a change in pull request #2497:
URL: https://github.com/apache/ozone/pull/2497#discussion_r689617353



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File path: hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/placement/algorithms/SCMContainerPlacementRackScatter.java
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@@ -0,0 +1,343 @@
+/**
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.hdds.scm.container.placement.algorithms;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Preconditions;
+import org.apache.hadoop.hdds.conf.ConfigurationSource;
+import org.apache.hadoop.hdds.protocol.DatanodeDetails;
+import org.apache.hadoop.hdds.scm.ContainerPlacementStatus;
+import org.apache.hadoop.hdds.scm.SCMCommonPlacementPolicy;
+import org.apache.hadoop.hdds.scm.exceptions.SCMException;
+import org.apache.hadoop.hdds.scm.net.InnerNode;
+import org.apache.hadoop.hdds.scm.net.NetConstants;
+import org.apache.hadoop.hdds.scm.net.NetworkTopology;
+import org.apache.hadoop.hdds.scm.net.Node;
+import org.apache.hadoop.hdds.scm.node.DatanodeInfo;
+import org.apache.hadoop.hdds.scm.node.NodeManager;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+/**
+ * Container placement policy that scatter datanodes on different racks
+ * , together with the space to satisfy the size constraints.
+ * <p>
+ * This placement policy will try to distribute datanodes on as many racks as
+ * possible.
+ * <p>
+ * This implementation applies to network topology like "/rack/node". Don't
+ * recommend to use this if the network topology has more layers.
+ * <p>
+ */
+public final class SCMContainerPlacementRackScatter
+    extends SCMCommonPlacementPolicy {
+  @VisibleForTesting
+  public static final Logger LOG =
+      LoggerFactory.getLogger(SCMContainerPlacementRackScatter.class);
+  private final NetworkTopology networkTopology;
+  private static final int RACK_LEVEL = 1;
+  private static final int MAX_RETRY= 3;
+  private final SCMContainerPlacementMetrics metrics;
+
+  /**
+   * Constructs a Container Placement with rack awareness.
+   *
+   * @param nodeManager Node Manager
+   * @param conf Configuration
+   */
+  public SCMContainerPlacementRackScatter(final NodeManager nodeManager,
+      final ConfigurationSource conf, final NetworkTopology networkTopology,
+      boolean fallback, final SCMContainerPlacementMetrics metrics) {
+    super(nodeManager, conf);
+    this.networkTopology = networkTopology;
+    this.metrics = metrics;
+  }
+
+  /**
+   * Called by SCM to choose datanodes.
+   *
+   *
+   * @param excludedNodes - list of the datanodes to exclude.
+   * @param favoredNodes - list of nodes preferred. This is a hint to the
+   *                     allocator, whether the favored nodes will be used
+   *                     depends on whether the nodes meets the allocator's
+   *                     requirement.
+   * @param nodesRequired - number of datanodes required.
+   * @param dataSizeRequired - size required for the container.
+   * @param metadataSizeRequired - size required for Ratis metadata.
+   * @return List of datanodes.
+   * @throws SCMException  SCMException
+   */
+  @Override
+  public List<DatanodeDetails> chooseDatanodes(
+      List<DatanodeDetails> excludedNodes, List<DatanodeDetails> favoredNodes,
+      int nodesRequired, long metadataSizeRequired, long dataSizeRequired)
+      throws SCMException {
+    Preconditions.checkArgument(nodesRequired > 0);
+    metrics.incrDatanodeRequestCount(nodesRequired);
+    int datanodeCount = networkTopology.getNumOfLeafNode(NetConstants.ROOT);
+    int excludedNodesCount = excludedNodes == null ? 0 : excludedNodes.size();
+    if (datanodeCount < nodesRequired + excludedNodesCount) {
+      throw new SCMException("No enough datanodes to choose. " +
+          "TotalNode = " + datanodeCount +
+          " RequiredNode = " + nodesRequired +
+          " ExcludedNode = " + excludedNodesCount, null);
+    }
+
+    List<DatanodeDetails> mutableFavoredNodes = new ArrayList<>();
+    if (favoredNodes != null) {
+      // Generate mutableFavoredNodes, only stores valid favoredNodes
+      for (DatanodeDetails datanodeDetails : favoredNodes) {
+        if (isValidNode(datanodeDetails, metadataSizeRequired,
+            dataSizeRequired)) {
+          mutableFavoredNodes.add(datanodeDetails);
+        }
+      }
+    }
+    if (excludedNodes != null) {
+      mutableFavoredNodes.removeAll(excludedNodes);
+    }
+
+    // For excluded nodes, we sort their racks at rear
+    List<Node> racks = getAllRacks();
+    if (excludedNodes != null && excludedNodes.size() > 0) {
+      racks = sortRackWithExcludedNodes(racks, excludedNodes);
+    }
+
+    List<Node> toChooseRack = new LinkedList<>(racks);
+    List<Node> chosenNodes = new ArrayList<>();
+    List<Node> unavailableNodes = new ArrayList<>();
+    if (excludedNodes != null) {
+      unavailableNodes.addAll(excludedNodes);
+    }
+
+    // If the result doesn't change after retryCount, we return with exception
+    int retryCount = 0;
+    while (nodesRequired > 0) {
+      if (retryCount > MAX_RETRY) {
+        throw new SCMException("No satisfied datanode to meet the" +
+            " excludedNodes and affinityNode constrains.", null);
+      }
+      int chosenListSize = chosenNodes.size();
+
+      if (toChooseRack.size() == 0) {
+        toChooseRack.addAll(racks);

Review comment:
       > Do we need to remove all the racks in chosenNodes here?
   
   I think we don't need to remove the content of chosenNodes. The size of chosenNodes could be used the check if it's a retry or not.
   
   > When do we expect the loop to run again for a retry? Is this related to fallback, or do we just retry a few times if we don't find enough nodes on unique racks?
   
   If the size of chosenNodes doesn't change, we treat it as a retry, and if the size doesn't change for RETRY_MAX times, then we return with exception.
   




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