Dart: Skip final getCounters, postFinish to idle historicals. (#17255) (#17259)

In a Dart query, all Historicals are given worker IDs, but not all of them
are going to actually be started or receive work orders.

Attempting to send a getCounters or postFinish command to a worker that
never received a work order is not only wasteful, but it causes errors due
to the workers not knowing about that query ID.

Co-authored-by: Gian Merlino <gianmerlino@gmail.com>

extensions-core/multi-stage-query/src/main/java/org/apache/druid/msq/exec/ControllerImpl.java

@@ -432,8 +432,10 @@ public class ControllerImpl implements Controller
       }
     }
     if (queryKernel != null && queryKernel.isSuccess()) {
-      // If successful, encourage the tasks to exit successfully.
-      postFinishToAllTasks();
+      // If successful, encourage workers to exit successfully.
+      // Only send this command to participating workers. For task-based queries, this is all tasks, since tasks
+      // are launched only when needed. For Dart, this is any servers that were actually assigned work items.
+      postFinishToWorkers(queryKernel.getAllParticipatingWorkers());
       workerManager.stop(false);
     } else {
       // If not successful, cancel running tasks.
@@ -1456,15 +1458,15 @@ public class ControllerImpl implements Controller
     return IntervalUtils.difference(replaceIntervals, publishIntervals);
   }
 
-  private CounterSnapshotsTree getCountersFromAllTasks()
+  private CounterSnapshotsTree fetchCountersFromWorkers(final IntSet workers)
   {
     final CounterSnapshotsTree retVal = new CounterSnapshotsTree();
     final List<String> taskList = getWorkerIds();
 
     final List<ListenableFuture<CounterSnapshotsTree>> futures = new ArrayList<>();
 
-    for (String taskId : taskList) {
-      futures.add(netClient.getCounters(taskId));
+    for (int workerNumber : workers) {
+      futures.add(netClient.getCounters(taskList.get(workerNumber)));
     }
 
     final List<CounterSnapshotsTree> snapshotsTrees =
@@ -1477,14 +1479,14 @@ public class ControllerImpl implements Controller
     return retVal;
   }
 
-  private void postFinishToAllTasks()
+  private void postFinishToWorkers(final IntSet workers)
   {
     final List<String> taskList = getWorkerIds();
 
     final List<ListenableFuture<Void>> futures = new ArrayList<>();
 
-    for (String taskId : taskList) {
-      futures.add(netClient.postFinish(taskId));
+    for (int workerNumber : workers) {
+      futures.add(netClient.postFinish(taskList.get(workerNumber)));
     }
 
     FutureUtils.getUnchecked(MSQFutureUtils.allAsList(futures, true), true);
@@ -1499,7 +1501,7 @@ public class ControllerImpl implements Controller
   private CounterSnapshotsTree getFinalCountersSnapshot(@Nullable final ControllerQueryKernel queryKernel)
   {
     if (queryKernel != null && queryKernel.isSuccess()) {
-      return getCountersFromAllTasks();
+      return fetchCountersFromWorkers(queryKernel.getAllParticipatingWorkers());
     } else {
       return makeCountersSnapshotForLiveReports();
     }

extensions-core/multi-stage-query/src/main/java/org/apache/druid/msq/kernel/controller/ControllerQueryKernel.java

@@ -27,6 +27,7 @@ import it.unimi.dsi.fastutil.ints.Int2IntAVLTreeMap;
 import it.unimi.dsi.fastutil.ints.Int2IntMap;
 import it.unimi.dsi.fastutil.ints.Int2ObjectAVLTreeMap;
 import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
+import it.unimi.dsi.fastutil.ints.IntAVLTreeSet;
 import it.unimi.dsi.fastutil.ints.IntSet;
 import org.apache.druid.frame.key.ClusterByPartitions;
 import org.apache.druid.java.util.common.IAE;
@@ -643,6 +644,20 @@ public class ControllerQueryKernel
     doWithStageTracker(stageId, ControllerStageTracker::fail);
   }
 
+  /**
+   * Returns the set of all worker numbers that have participated in work done so far by this query.
+   */
+  public IntSet getAllParticipatingWorkers()
+  {
+    final IntSet retVal = new IntAVLTreeSet();
+
+    for (final ControllerStageTracker tracker : stageTrackers.values()) {
+      retVal.addAll(tracker.getWorkerInputs().workers());
+    }
+
+    return retVal;
+  }
+
   /**
    * Fetches and returns the stage kernel corresponding to the provided stage id, else throws {@link IAE}
    */

extensions-core/multi-stage-query/src/main/java/org/apache/druid/msq/kernel/controller/ControllerStageTracker.java

@@ -63,7 +63,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.TreeMap;
-import java.util.stream.IntStream;
 
 /**
  * Controller-side state machine for each stage. Used by {@link ControllerQueryKernel} to form the overall state
@@ -137,7 +136,7 @@ class ControllerStageTracker
     this.workerInputs = workerInputs;
     this.maxRetainedPartitionSketchBytes = maxRetainedPartitionSketchBytes;
 
-    initializeWorkerState(workerCount);
+    initializeWorkerState(workerInputs.workers());
 
     if (stageDef.mustGatherResultKeyStatistics()) {
       this.completeKeyStatisticsInformation =
@@ -149,14 +148,13 @@ class ControllerStageTracker
   }
 
   /**
-   * Initialize stage for each worker to {@link ControllerWorkerStagePhase#NEW}
-   *
-   * @param workerCount
+   * Initialize stage for each worker to {@link ControllerWorkerStagePhase#NEW}.
    */
-  private void initializeWorkerState(int workerCount)
+  private void initializeWorkerState(IntSet workers)
   {
-    IntStream.range(0, workerCount)
-             .forEach(wokerNumber -> workerToPhase.put(wokerNumber, ControllerWorkerStagePhase.NEW));
+    for (int workerNumber : workers) {
+      workerToPhase.put(workerNumber, ControllerWorkerStagePhase.NEW);
+    }
   }
 
   /**