[GitHub] [helix] xyuanlu commented on a change in pull request #1307: Add TrieClusterTopology for retrieving hierarchical topology

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

xyuanlu commented on a change in pull request #1307:
URL: https://github.com/apache/helix/pull/1307#discussion_r476662851



##########
File path: helix-core/src/main/java/org/apache/helix/model/TrieClusterTopology.java
##########
@@ -0,0 +1,244 @@
+package org.apache.helix.model;
+
+/*
+ * 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.
+ */
+
+import java.util.ArrayDeque;
+import java.util.Arrays;
+import java.util.Deque;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import org.apache.helix.HelixException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * This is a class that uses a trie data structure to represent cluster topology. Each node
+ * except the terminal node represents a certain domain in the topology, and an terminal node
+ * represents an instance in the cluster.
+ */
+public class TrieClusterTopology {
+  private static Logger logger = LoggerFactory.getLogger(TrieClusterTopology.class);
+  private static final String DELIMITER = "/";
+  private static final String CONNECTOR = "_";
+
+  private final TrieNode _rootNode;
+  private final String[] _topologyKeys;
+
+  public TrieClusterTopology(final List<String> liveNodes,
+      final Map<String, InstanceConfig> instanceConfigMap, ClusterConfig clusterConfig) {
+    if (instanceConfigMap == null || !instanceConfigMap.keySet().containsAll(liveNodes)) {
+      throw new HelixException(String.format("Config for instances %s is not found!",
+          instanceConfigMap == null ? liveNodes : liveNodes.removeAll(instanceConfigMap.keySet())));
+    }
+    // A list of all keys in cluster topology, e.g., a cluster topology defined as
+    // /group/zone/rack/instance will return ["group", "zone", "rack", "instance"].
+    _topologyKeys = Arrays.asList(clusterConfig.getTopology().trim().split(DELIMITER)).stream()
+        .filter(str -> !str.isEmpty()).collect(Collectors.toList()).toArray(new String[0]);
+    _rootNode = new TrieNode(new HashMap<>(), DELIMITER);
+    constructTrie(instanceConfigMap);
+  }
+
+  /**
+   * Return the topology of a cluster as a map. The key of the map is the first level of
+   * domain, and the value is a set of string that represents the path to each end node in that
+   * domain. E.g., assume the topology is defined as /group/zone/rack/instance, the result may be {
+   * ["group_0": {"zone_0/rack_0/instance_0", "zone_1/rack_1/instance_1"}], ["group_1": {"zone_1
+   * /rack_1/instance_1", "zone_1/rack_1/instance_2"}]}
+   */
+  public Map<String, Set<String>> getClusterTopology() {
+    return getTopologyUnderDomain(new HashMap<>());
+  }
+
+  /**
+   * Return the topology under a certain domain as a map. The key of the returned map is the next
+   * level domain, and the value is a set of string that represents the path to each end node in
+   * that domain.
+   * @param domain A map defining the domain name and its value, e.g. {["group": "1"], ["zone",
+   *               "2"]}
+   * @return the topology under the given domain, e.g. {["rack_0": {"instance_0", "instance_1"},
+   * ["rack_1": {"instance_2", "instance_3"}]}
+   */
+  public Map<String, Set<String>> getTopologyUnderDomain(Map<String, String> domain) {
+    LinkedHashMap<String, String> orderedDomain = validateAndOrderDomain(domain);
+    TrieNode startNode = getStartNode(orderedDomain);
+    Map<String, TrieNode> children = startNode.getChildren();
+    Map<String, Set<String>> results = new HashMap<>();
+    children.entrySet().forEach(child -> {
+      String key = child.getKey();
+      results.put(key,
+          truncatePath(getPathUnderNode(child.getValue()), child.getValue().getPath() + DELIMITER));
+    });
+    return results;
+  }
+
+  /**
+   * Validate the domain provided has continuous fields in cluster topology definition. If it
+   * has, order the domain based on cluster topology definition. E.g. if the cluster topology is
+   * /group/zone/rack/instance, and domain is provided as {["zone": "1"], ["group", "2"]} will be
+   * reordered in a LinkedinHashMap as {["group", "2"], ["zone": "1"]}
+   */
+  private LinkedHashMap<String, String> validateAndOrderDomain(Map<String, String> domain) {
+    LinkedHashMap<String, String> orderedDomain = new LinkedHashMap<>();
+    if (domain == null) {
+      throw new IllegalArgumentException("The domain should not be null");
+    }
+    for (int i = 0; i < domain.size(); i++) {
+      if (!domain.containsKey(_topologyKeys[i])) {
+        throw new IllegalArgumentException(String
+            .format("The input domain is not valid, the key %s is required", _topologyKeys[i]));
+      } else {
+        orderedDomain.put(_topologyKeys[i], domain.get(_topologyKeys[i]));
+      }
+    }
+    return orderedDomain;
+  }
+
+  /**
+   * Truncate each path in the given set and only retain path starting from current node's
+   * children to each end node.
+   * @param toRemovePath The path from root to current node. It should be removed so that users
+   *                     can get a better view.
+   */
+  private Set<String> truncatePath(Set<String> paths, String toRemovePath) {
+    Set<String> results = new HashSet<>();
+    paths.forEach(path -> {
+      String truncatedPath = path.replace(toRemovePath, "");
+      results.add(truncatedPath);
+    });
+    return results;
+  }
+
+  /**
+   * Return all the paths from a TrieNode as a set.
+   * @param node the node from where to collect all the nodes' paths.
+   * @return All the paths under the node.
+   */
+  private Set<String> getPathUnderNode(TrieNode node) {
+    Set<String> resultMap = new HashSet<>();
+    Deque<TrieNode> nodeStack = new ArrayDeque<>();
+    nodeStack.push(node);
+    while (!nodeStack.isEmpty()) {
+      node = nodeStack.pop();
+      if (node.getChildren().isEmpty()) {
+        resultMap.add(node.getPath());
+      } else {
+        for (TrieNode child : node.getChildren().values()) {
+          nodeStack.push(child);
+        }
+      }
+    }
+    return resultMap;
+  }
+
+  private TrieNode getStartNode(LinkedHashMap<String, String> domain) {
+    TrieNode curNode = _rootNode;
+    TrieNode nextNode;
+    for (Map.Entry<String, String> entry : domain.entrySet()) {
+      nextNode = curNode.getChildren().get(entry.getKey() + CONNECTOR + entry.getValue());
+      if (nextNode == null) {
+        throw new IllegalArgumentException(String
+            .format("The input domain %s does not have the value %s", entry.getKey(),
+                entry.getValue()));
+      }
+      curNode = nextNode;
+    }
+    return curNode;
+  }
+
+  private void removeInvalidInstanceConfig(Map<String, InstanceConfig> instanceConfigMap) {
+    Set<String> toRemoveConfig = new HashSet<>();
+    for (String instanceName : instanceConfigMap.keySet()) {
+      Map<String, String> domainAsMap = instanceConfigMap.get(instanceName).getDomainAsMap();
+      if (domainAsMap.isEmpty()) {
+        logger.info(String.format("Domain for instance %s is not set", instanceName));
+        toRemoveConfig.add(instanceName);
+      } else {
+        for (String key : _topologyKeys) {
+          String value = domainAsMap.get(key);
+          if (value == null || value.length() == 0) {
+            logger.info(String.format("Domain %s for instance %s is not set",
+                domainAsMap.get(key), instanceName));
+            toRemoveConfig.add(instanceName);
+            break;
+          }
+        }
+      }
+    }
+    toRemoveConfig.forEach(entry -> instanceConfigMap.remove(entry));
+  }
+
+  /**
+   * Constructs a trie based on the provided instance config map. It loops through all instance
+   * configs and constructs the trie in a top down manner.
+   */
+  private void constructTrie(Map<String, InstanceConfig> instanceConfigMap) {
+    removeInvalidInstanceConfig(instanceConfigMap);
+    Map<String, Map<String, String>> instanceDomainsMap = new HashMap<>();
+    instanceConfigMap.entrySet().forEach(
+        entry -> instanceDomainsMap.put(entry.getKey(), entry.getValue().getDomainAsMap()));
+
+    for (Map.Entry<String, Map<String, String>> entry : instanceDomainsMap.entrySet()) {
+      TrieNode curNode = _rootNode;
+      String path = "";
+      for (int i = 0; i < _topologyKeys.length; i++) {
+        String key = _topologyKeys[i] + CONNECTOR + entry.getValue().get(_topologyKeys[i]);

Review comment:
       Thanks for the detailed reply.
   
   I think the previous 3 points can be achieved by adding a flag and using non static 'DEFAULT_DOMAIN_PREFIX'. 
   For the point 4, 
   Please correct me if I am wrong, line 288 in constructTrie will also add a "default" node similar to 'clusterTopologyKeyDefaultValue'. Maybe we could read the tree and bypass default node. 
   
   
   In my own opinion, I think the question would be, do we construct topology tree in class Topology for these instances? If yes, its better to read from the existing tree. If not, I think it's ok to have another orthogonal data structure representing the hierarchy. 




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