[GitHub] [pinot] jackjlli commented on a diff in pull request #8434: Add replica group based instance assigment algorithm with FD awareness

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

jackjlli commented on code in PR #8434:
URL: https://github.com/apache/pinot/pull/8434#discussion_r891508410


##########
pinot-spi/src/main/java/org/apache/pinot/spi/config/table/assignment/InstanceAssignmentConfig.java:
##########
@@ -28,6 +28,8 @@
 
 public class InstanceAssignmentConfig extends BaseJsonConfig {
 
+  @JsonPropertyDescription("Configuration for the strategy to assign instances to partitions")
+  public final PartitionSelector _partitionSelector;

Review Comment:
   Make it private since you've already had a getter method?



##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/assignment/instance/FDAwareInstancePartitionSelector.java:
##########
@@ -0,0 +1,455 @@
+/**
+ * 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.pinot.controller.helix.core.assignment.instance;
+
+import com.google.common.base.Preconditions;
+import java.util.ArrayList;
+import java.util.Deque;
+import java.util.HashMap;
+import java.util.LinkedHashSet;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.NavigableMap;
+import java.util.Optional;
+import java.util.TreeMap;
+import java.util.stream.Collectors;
+import javax.annotation.Nullable;
+import org.apache.commons.lang3.tuple.ImmutablePair;
+import org.apache.commons.lang3.tuple.Pair;
+import org.apache.helix.model.InstanceConfig;
+import org.apache.pinot.common.assignment.InstancePartitions;
+import org.apache.pinot.spi.config.table.assignment.InstanceReplicaGroupPartitionConfig;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * The instance replica-group/partition selector is responsible for selecting the instances for every replica-group/
+ * partition, with each fault-domain mapping 1:1 to a server pool
+ * Algorithm details and proof see
+ * https://docs.google.com/document/d/1KmJ1DsYXVdzrojj_JYBHRJ2gRMQ5y-o63YqPs7ei7nI/edit#heading=h.nrxxvujq7ael
+ */
+public class FDAwareInstancePartitionSelector extends InstancePartitionSelector {
+  private static final Logger LOGGER = LoggerFactory.getLogger(FDAwareInstancePartitionSelector.class);
+
+  public FDAwareInstancePartitionSelector(InstanceReplicaGroupPartitionConfig replicaGroupPartitionConfig,
+      String tableNameWithType, @Nullable InstancePartitions existingInstancePartitions) {
+    super(replicaGroupPartitionConfig, tableNameWithType, existingInstancePartitions);
+  }
+
+  /**
+   * @return pair of (numFaultDomains, numTotalInstances)
+   */
+  private Pair<Integer, Integer> processFaultDomainPreconditions(
+      Map<Integer, List<InstanceConfig>> faultDomainToInstanceConfigsMap) {
+    int numFDs = faultDomainToInstanceConfigsMap.size();
+    Preconditions.checkState(numFDs != 0, "No pool (fault-domain) qualified for selection");
+
+    // Collect the number of instances in each FD into a list and sort
+    List<Integer> numInstancesPerFD =
+        faultDomainToInstanceConfigsMap.values().stream().map(List::size).sorted().collect(Collectors.toList());
+    // Should have non-zero total instances
+    Optional<Integer> totalInstancesOptional = numInstancesPerFD.stream().reduce(Integer::sum);
+    Preconditions.checkState(totalInstancesOptional.orElse(0) > 0, "The number of total instances is zero");
+    int numTotalInstances = totalInstancesOptional.get();
+    // Assume best-effort round-robin assignment of instances to FDs, the assignment should be balanced
+    // i.e., the difference between max num instances and min num instances should be at most 1
+    Preconditions.checkState(numInstancesPerFD.get(numInstancesPerFD.size() - 1) - numInstancesPerFD.get(0) <= 1,
+        "The instances are not balanced for each pool (fault-domain)");
+    return new ImmutablePair<>(numFDs, numTotalInstances);
+  }
+
+  /**
+   * @return (numReplicaGroups, numInstancesPerReplicaGroup)
+   */
+  private Pair<Integer, Integer> processReplicaGroupAssignmentPreconditions(int numFaultDomains, int numTotalInstances,
+      InstanceReplicaGroupPartitionConfig replicaGroupPartitionConfig) {
+    int numReplicaGroups = replicaGroupPartitionConfig.getNumReplicaGroups();
+    Preconditions.checkState(numReplicaGroups > 0, "Number of replica-groups must be positive");
+    int numInstancesPerReplicaGroup = replicaGroupPartitionConfig.getNumInstancesPerReplicaGroup();
+    if (numInstancesPerReplicaGroup > 0) {
+      int numInstancesToSelect = numInstancesPerReplicaGroup * numReplicaGroups;
+
+      Preconditions.checkState(numInstancesToSelect <= numTotalInstances,
+          "Not enough qualified instances (%s in all FDs, asked for %s)", numTotalInstances, numInstancesToSelect);

Review Comment:
   How about rephrasing the sentence to `ask for: (numInstancesPerReplicaGroup: %d) *  (numReplicaGroups: %d) = %d` to give better explanation?



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