[To dev/1.3] Load balance patch (#17463) (#17493) (#17527)

Author: CRZbulabula

iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/manager/load/service/EventService.java

@@ -114,6 +114,11 @@ public void stopEventService() {
         currentEventServiceFuture = null;
         LOGGER.info("Event service is stopped successfully.");
       }
+      synchronized (this) {
+        previousNodeStatisticsMap.clear();
+        previousRegionGroupStatisticsMap.clear();
+        previousConsensusGroupStatisticsMap.clear();
+      }
     }
   }
 

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/analyze/ClusterPartitionFetcher.java

@@ -59,7 +59,6 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
-import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -421,16 +420,31 @@ private SchemaPartition parseSchemaPartitionTableResp(
       String database = entry1.getKey();
       final Map<TSeriesPartitionSlot, TRegionReplicaSet> result1 =
           regionReplicaMap.computeIfAbsent(database, k -> new HashMap<>());
+      Map<TSeriesPartitionSlot, TConsensusGroupId> seriesPartitionTable = entry1.getValue();
+
+      if (seriesPartitionTable.size() == 1) {
+        // Fast collection in case of query for single device
+        Map.Entry<TSeriesPartitionSlot, TConsensusGroupId> seriesPartitionEntry =
+            seriesPartitionTable.entrySet().iterator().next();
+        List<TRegionReplicaSet> regionReplicaSets =
+            partitionCache.getRegionReplicaSet(
+                Collections.singletonList(seriesPartitionEntry.getValue()));
+        result1.put(seriesPartitionEntry.getKey(), regionReplicaSets.get(0));
+        continue;
+      }
 
-      Map<TSeriesPartitionSlot, TConsensusGroupId> orderedMap =
-          new LinkedHashMap<>(entry1.getValue());
-      List<TConsensusGroupId> orderedGroupIds = new ArrayList<>(orderedMap.values());
+      List<TConsensusGroupId> distinctRegionGroupIds =
+          new ArrayList<>(new HashSet<>(seriesPartitionTable.values()));
       List<TRegionReplicaSet> regionReplicaSets =
-          partitionCache.getRegionReplicaSet(orderedGroupIds);
+          partitionCache.getRegionReplicaSet(distinctRegionGroupIds);
+      Map<TConsensusGroupId, TRegionReplicaSet> groupIdToReplicaSet = new HashMap<>();
+      for (int index = 0; index < distinctRegionGroupIds.size(); index++) {
+        groupIdToReplicaSet.put(distinctRegionGroupIds.get(index), regionReplicaSets.get(index));
+      }
 
-      int index = 0;
-      for (Map.Entry<TSeriesPartitionSlot, TConsensusGroupId> entry2 : orderedMap.entrySet()) {
-        result1.put(entry2.getKey(), regionReplicaSets.get(index++));
+      for (Map.Entry<TSeriesPartitionSlot, TConsensusGroupId> entry2 :
+          seriesPartitionTable.entrySet()) {
+        result1.put(entry2.getKey(), groupIdToReplicaSet.get(entry2.getValue()));
       }
     }