[GitHub] [pinot] snleee commented on a diff in pull request #9309: Introduce Segment AssignmentStrategy Interface

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

snleee commented on code in PR #9309:
URL: https://github.com/apache/pinot/pull/9309#discussion_r966612919


##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/assignment/segment/BaseSegmentAssignment.java:
##########
@@ -85,70 +89,41 @@ public void init(HelixManager helixManager, TableConfig tableConfig) {
       _logger.info("Initialized with replication: {} and partition column: {} for table: {}", _replication,
           _partitionColumn, _tableNameWithType);
     }
+    setSegmentAssignmentStrategyMap(instancePartitionsMap);
   }
 
   /**
-   * Returns the replication of the table.
+   * Sets Segment assignment strategy for different instance partitions and puts into a map of
+   * Map<InstancePartitionsType, SegmentAssignmentStrategy>
    */
-  protected abstract int getReplication(TableConfig tableConfig);
+  protected void setSegmentAssignmentStrategyMap(
+      Map<InstancePartitionsType, InstancePartitions> instancePartitionsMap) {
+      _assignmentStrategyMap = SegmentAssignmentStrategyFactory.getSegmentAssignmentStrategy(_helixManager,
+          _tableConfig, instancePartitionsMap);
+  }
 
   /**
-   * Helper method to check whether the number of replica-groups matches the table replication for replica-group based
-   * instance partitions. Log a warning if they do not match and use the one inside the instance partitions. The
-   * mismatch can happen when table is not configured correctly (table replication and numReplicaGroups does not match
-   * or replication changed without reassigning instances).
+   * Returns the replication of the table.
    */
-  protected void checkReplication(InstancePartitions instancePartitions) {
-    int numReplicaGroups = instancePartitions.getNumReplicaGroups();
-    if (numReplicaGroups != _replication) {
-      _logger.warn(
-          "Number of replica-groups in instance partitions {}: {} does not match replication in table config: {} for "
-              + "table: {}, using: {}", instancePartitions.getInstancePartitionsName(), numReplicaGroups, _replication,
-          _tableNameWithType, numReplicaGroups);
-    }
-  }
+  protected abstract int getReplication(TableConfig tableConfig);
 
   /**
    * Helper method to assign instances based on the current assignment and instance partitions.
    */
   protected List<String> assignSegment(String segmentName, Map<String, Map<String, String>> currentAssignment,

Review Comment:
   I think that we can remove this helper method and directly call the following line in `OfflineSegmentAssignment/RealtimeSegmentAssignment`
   ```
   segmentAssignmentStrategy.assignSegment(segmentName,
           currentAssignment, instancePartitions, instancePartitionsType);
   ```



##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/assignment/segment/SegmentAssignment.java:
##########
@@ -31,20 +31,17 @@
 
 /**
  * Interface for segment assignment and table rebalance.
- * <p>
- * TODO: Add SegmentAssignmentStrategy interface and support custom segment assignment strategy (e.g. cost based segment
- *       assignment). SegmentAssignmentStrategy should not be coupled with SegmentAssignment, and SegmentAssignment
- *       should be able to choose the segment assignment strategy based on the configuration.
  */
 public interface SegmentAssignment {
 
   /**
    * Initializes the segment assignment.
-   *
    * @param helixManager Helix manager
    * @param tableConfig Table config
+   * @param instancePartitionsMap Map from type (OFFLINE|CONSUMING|COMPLETED) to instance partitions
    */
-  void init(HelixManager helixManager, TableConfig tableConfig);
+  void init(HelixManager helixManager, TableConfig tableConfig,
+      Map<InstancePartitionsType, InstancePartitions> instancePartitionsMap);

Review Comment:
   I don't think that we need to add `instancePartitionsMap` here if we initialize the segment assignment once in the beginning of
   
   1. assignSegment()
   
   2. rebalanceTable()
   
   and pass the object around.



##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/assignment/segment/strategy/SegmentAssignmentStrategyFactory.java:
##########
@@ -0,0 +1,114 @@
+/**
+ * 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.segment.strategy;
+
+import java.util.HashMap;
+import java.util.Map;
+import org.apache.helix.HelixManager;
+import org.apache.pinot.common.assignment.InstancePartitions;
+import org.apache.pinot.spi.config.table.TableConfig;
+import org.apache.pinot.spi.config.table.TableType;
+import org.apache.pinot.spi.config.table.assignment.InstancePartitionsType;
+import org.apache.pinot.spi.config.table.assignment.SegmentAssignmentConfig;
+import org.apache.pinot.spi.utils.CommonConstants.Segment.AssignmentStrategy;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * Factory for SegmentAssignmentStrategy
+ */
+public class SegmentAssignmentStrategyFactory {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(SegmentAssignmentStrategyFactory.class);
+  private SegmentAssignmentStrategyFactory() {
+  }
+
+  /**
+   * Determine Segment Assignment strategy
+   */
+  public static Map<InstancePartitionsType, SegmentAssignmentStrategy>
+  getSegmentAssignmentStrategy(HelixManager helixManager,

Review Comment:
   I feel that this logic becomes too complex if we also need to handle all of `OFFLINE/CONSUMING/COMPLETED`. I think that we should consider keeping this factory to be very thin (given an `AssignmentStrategy` enum, return the correct object).
   
   Instead, we should think about putting the logic for picking the correct assignment in each `OfflineSegmentAssignment / RealtimeSegmentAssignment`.
   
   This will make this logic less complex because we just need to handle `OFFLINE` from `OfflineSegmentAssignment` and `CONSUMING/COMPLETED` from `RealtimeSegmentAssignment`.
   
   
   
   



##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/assignment/segment/RealtimeSegmentAssignment.java:
##########
@@ -183,8 +176,10 @@ public Map<String, Map<String, String>> rebalanceTable(Map<String, Map<String, S
         config.getBoolean(RebalanceConfigConstants.BOOTSTRAP, RebalanceConfigConstants.DEFAULT_BOOTSTRAP);
 
     // Rebalance tiers first
+    SegmentAssignmentStrategy segmentAssignmentStrategy = _assignmentStrategyMap.get(InstancePartitionsType.COMPLETED);

Review Comment:
   Why don't we initialize the segmentAssignmentStrategy directly from `SegmentAssignmentStrategyFactory` here?
   
   In that case, we won't need to change the interface for `SegmentAssignment:init()` to take the `instancePartitionsMap`.



##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/assignment/segment/BaseSegmentAssignment.java:
##########
@@ -194,60 +171,16 @@ protected Map<String, Map<String, String>> reassignSegments(String instanceParti
       // When bootstrap is enabled, start with an empty assignment and reassign all segments
       newAssignment = new TreeMap<>();
       for (String segment : currentAssignment.keySet()) {
-        List<String> assignedInstances = assignSegment(segment, newAssignment, instancePartitions);
+        List<String> assignedInstances = assignSegment(segment, newAssignment, instancePartitions,

Review Comment:
   This can be simply
   ```
   List<String> assignedInstances = assignmentStrategy.assignSegment(...)
   ```



##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/assignment/segment/BaseSegmentAssignment.java:
##########
@@ -68,11 +68,15 @@ public abstract class BaseSegmentAssignment implements SegmentAssignment {
   protected String _tableNameWithType;
   protected int _replication;
   protected String _partitionColumn;
+  protected TableConfig _tableConfig;
+  protected Map<InstancePartitionsType, SegmentAssignmentStrategy> _assignmentStrategyMap;
 
   @Override
-  public void init(HelixManager helixManager, TableConfig tableConfig) {
+  public void init(HelixManager helixManager, TableConfig tableConfig,
+      Map<InstancePartitionsType, InstancePartitions> instancePartitionsMap) {
     _helixManager = helixManager;
     _tableNameWithType = tableConfig.getTableName();
+    _tableConfig = tableConfig;

Review Comment:
   Do we access this from anywhere? For `setSegmentAssignmentStrategyMap()`, we can push the local `tableConfig`?



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