Add group_trim_size and error_on_num_groups_limit hints/options.

pinot-common/src/main/java/org/apache/pinot/common/utils/config/QueryOptionsUtils.java

@@ -268,6 +268,10 @@ public static Integer getMultiStageLeafLimit(Map<String, String> queryOptions) {
     return checkedParseIntNonNegative(QueryOptionKey.MULTI_STAGE_LEAF_LIMIT, maxLeafLimitStr);
   }
 
+  public static boolean getErrorOnNumGroupsLimit(Map<String, String> queryOptions) {
+    return Boolean.parseBoolean(queryOptions.get(QueryOptionKey.ERROR_ON_NUM_GROUPS_LIMIT));
+  }
+
   @Nullable
   public static Integer getNumGroupsLimit(Map<String, String> queryOptions) {
     String maxNumGroupLimit = queryOptions.get(QueryOptionKey.NUM_GROUPS_LIMIT);

pinot-controller/src/main/java/org/apache/pinot/controller/helix/ControllerRequestClient.java

@@ -25,6 +25,8 @@
 import java.net.URISyntaxException;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashMap;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import javax.annotation.Nullable;
@@ -244,6 +246,42 @@ public List<String> listSegments(String tableName, @Nullable String tableType, b
     }
   }
 
+  public Map<String, List<String>> getServersToSegmentsMap(String tableName, TableType tableType)
+      throws IOException {
+    String url = _controllerRequestURLBuilder.forServersToSegmentsMap(tableName, tableType.toString());
+    try {
+      SimpleHttpResponse resp =
+          HttpClient.wrapAndThrowHttpException(_httpClient.sendGetRequest(new URI(url), _headers));
+      JsonNode jsonNode = JsonUtils.stringToJsonNode(resp.getResponse());
+      if (jsonNode == null || jsonNode.get(0) == null) {
+        return Collections.emptyMap();
+      }
+
+      JsonNode serversMap = jsonNode.get(0).get("serverToSegmentsMap");
+      if (serversMap == null) {
+        return Collections.emptyMap();
+      }
+
+      HashMap<String, List<String>> result = new HashMap<>();
+      Iterator<Map.Entry<String, JsonNode>> fields = serversMap.fields();
+      while (fields.hasNext()) {
+        Map.Entry<String, JsonNode> field = fields.next();
+        List<String> segments = new ArrayList<>();
+
+        ArrayNode value = (ArrayNode) field.getValue();
+        for (int i = 0, len = value.size(); i < len; i++) {
+          segments.add(value.get(i).toString());
+        }
+
+        result.put(field.getKey(), segments);
+      }
+
+      return result;
+    } catch (HttpErrorStatusException | URISyntaxException e) {
+      throw new IOException(e);
+    }
+  }
+
   public void deleteSegment(String tableName, String segmentName)
       throws IOException {
     try {

pinot-controller/src/test/java/org/apache/pinot/controller/helix/ControllerTest.java

@@ -728,6 +728,11 @@ public long getTableSize(String tableName)
     return getControllerRequestClient().getTableSize(tableName);
   }
 
+  public Map<String, List<String>> getTableServersToSegmentsMap(String tableName, TableType tableType)
+      throws IOException {
+    return getControllerRequestClient().getServersToSegmentsMap(tableName, tableType);
+  }
+
   public String reloadOfflineTable(String tableName)
       throws IOException {
     return reloadOfflineTable(tableName, false);

pinot-core/src/main/java/org/apache/pinot/core/operator/query/AggregationOperator.java

@@ -38,7 +38,7 @@
 
 
 /**
- * The <code>AggregationOperator</code> class provides the operator for aggregation only query on a single segment.
+ * The <code>AggregationOperator</code> class implements keyless aggregation query on a single segment in V1/SSQE.
  */
 @SuppressWarnings("rawtypes")
 public class AggregationOperator extends BaseOperator<AggregationResultsBlock> {

pinot-core/src/main/java/org/apache/pinot/core/operator/query/GroupByOperator.java

@@ -46,7 +46,7 @@
 
 
 /**
- * The <code>GroupByOperator</code> class provides the operator for group-by query on a single segment.
+ * The <code>GroupByOperator</code> class implements keyed aggregation on a single segment in V1/SSQE.
  */
 @SuppressWarnings("rawtypes")
 public class GroupByOperator extends BaseOperator<GroupByResultsBlock> {

pinot-core/src/main/java/org/apache/pinot/core/plan/CombinePlanNode.java

@@ -48,7 +48,8 @@
 
 
 /**
- * The <code>CombinePlanNode</code> class provides the execution plan for combining results from multiple segments.
+ * The <code>CombinePlanNode</code> class provides the execution plan for combining results from multiple segments in
+ * V1/SSQE.
  */
 @SuppressWarnings({"rawtypes", "unchecked"})
 public class CombinePlanNode implements PlanNode {

pinot-core/src/main/java/org/apache/pinot/core/query/aggregation/groupby/DictionaryBasedGroupKeyGenerator.java

@@ -53,7 +53,7 @@
  *     integer raw keys and map them onto contiguous group ids. (INT_MAP_BASED)
  *   </li>
  *   <li>
- *     If the maximum number of possible group keys cannot fit into than integer, but still fit into long, generate long
+ *     If the maximum number of possible group keys cannot fit into integer, but still fit into long, generate long
  *     raw keys and map them onto contiguous group ids. (LONG_MAP_BASED)
  *   </li>
  *   <li>
@@ -105,8 +105,6 @@ public class DictionaryBasedGroupKeyGenerator implements GroupKeyGenerator {
   public DictionaryBasedGroupKeyGenerator(BaseProjectOperator<?> projectOperator,
       ExpressionContext[] groupByExpressions, int numGroupsLimit, int arrayBasedThreshold,
       @Nullable Map<ExpressionContext, Integer> groupByExpressionSizesFromPredicates) {
-    assert numGroupsLimit >= arrayBasedThreshold;
-
     _groupByExpressions = groupByExpressions;
     _numGroupByExpressions = groupByExpressions.length;
 
@@ -173,7 +171,9 @@ public DictionaryBasedGroupKeyGenerator(BaseProjectOperator<?> projectOperator,
         _rawKeyHolder = new LongMapBasedHolder(groupIdMap);
       } else {
         _globalGroupIdUpperBound = Math.min((int) cardinalityProduct, numGroupsLimit);
-        if (cardinalityProduct > arrayBasedThreshold) {
+        // arrayBaseHolder fails with ArrayIndexOutOfBoundsException if numGroupsLimit < cardinalityProduct
+        // because array doesn't fit all (potentially unsorted) values
+        if (cardinalityProduct > arrayBasedThreshold || numGroupsLimit < cardinalityProduct) {
           // IntMapBasedHolder
           IntGroupIdMap groupIdMap = THREAD_LOCAL_INT_MAP.get();
           groupIdMap.clearAndTrim();
@@ -281,6 +281,7 @@ private interface RawKeyHolder {
     int getNumKeys();
   }
 
+  // This holder works only if it can fit all results, otherwise it fails on AIOOBE or produces too many group keys
   private class ArrayBasedHolder implements RawKeyHolder {
     private final boolean[] _flags = new boolean[_globalGroupIdUpperBound];
     private int _numKeys = 0;

pinot-core/src/main/java/org/apache/pinot/core/query/reduce/BrokerReduceService.java

@@ -58,8 +58,12 @@ public BrokerReduceService(PinotConfiguration config) {
     super(config);
   }
 
-  public BrokerResponseNative reduceOnDataTable(BrokerRequest brokerRequest, BrokerRequest serverBrokerRequest,
-      Map<ServerRoutingInstance, DataTable> dataTableMap, long reduceTimeOutMs, BrokerMetrics brokerMetrics) {
+  public BrokerResponseNative reduceOnDataTable(
+      BrokerRequest brokerRequest,
+      BrokerRequest serverBrokerRequest,
+      Map<ServerRoutingInstance, DataTable> dataTableMap,
+      long reduceTimeOutMs,
+      BrokerMetrics brokerMetrics) {
     if (dataTableMap.isEmpty()) {
       // Empty response.
       return BrokerResponseNative.empty();
@@ -70,12 +74,12 @@ public BrokerResponseNative reduceOnDataTable(BrokerRequest brokerRequest, Broke
         queryOptions != null && Boolean.parseBoolean(queryOptions.get(CommonConstants.Broker.Request.TRACE));
 
     ExecutionStatsAggregator aggregator = new ExecutionStatsAggregator(enableTrace);
-    BrokerResponseNative brokerResponseNative = new BrokerResponseNative();
+    BrokerResponseNative response = new BrokerResponseNative();
 
     // Cache a data schema from data tables (try to cache one with data rows associated with it).
-    DataSchema dataSchemaFromEmptyDataTable = null;
-    DataSchema dataSchemaFromNonEmptyDataTable = null;
-    List<ServerRoutingInstance> serversWithConflictingDataSchema = new ArrayList<>();
+    DataSchema schemaOfEmptyTable = null;
+    DataSchema schemaOfNonEmptyTable = null;
+    List<ServerRoutingInstance> serversWithConflictingSchema = new ArrayList<>();
 
     // Process server response metadata.
     Iterator<Map.Entry<ServerRoutingInstance, DataTable>> iterator = dataTableMap.entrySet().iterator();
@@ -93,19 +97,19 @@ public BrokerResponseNative reduceOnDataTable(BrokerRequest brokerRequest, Broke
       } else {
         // Try to cache a data table with data rows inside, or cache one with data schema inside.
         if (dataTable.getNumberOfRows() == 0) {
-          if (dataSchemaFromEmptyDataTable == null) {
-            dataSchemaFromEmptyDataTable = dataSchema;
+          if (schemaOfEmptyTable == null) {
+            schemaOfEmptyTable = dataSchema;
           }
           iterator.remove();
         } else {
-          if (dataSchemaFromNonEmptyDataTable == null) {
-            dataSchemaFromNonEmptyDataTable = dataSchema;
+          if (schemaOfNonEmptyTable == null) {
+            schemaOfNonEmptyTable = dataSchema;
           } else {
             // Remove data tables with conflicting data schema.
             // NOTE: Only compare the column data types, since the column names (string representation of expression)
             //       can change across different versions.
-            if (!Arrays.equals(dataSchema.getColumnDataTypes(), dataSchemaFromNonEmptyDataTable.getColumnDataTypes())) {
-              serversWithConflictingDataSchema.add(entry.getKey());
+            if (!Arrays.equals(dataSchema.getColumnDataTypes(), schemaOfNonEmptyTable.getColumnDataTypes())) {
+              serversWithConflictingSchema.add(entry.getKey());
               iterator.remove();
             }
           }
@@ -117,52 +121,51 @@ public BrokerResponseNative reduceOnDataTable(BrokerRequest brokerRequest, Broke
     String rawTableName = TableNameBuilder.extractRawTableName(tableName);
 
     // Set execution statistics and Update broker metrics.
-    aggregator.setStats(rawTableName, brokerResponseNative, brokerMetrics);
+    aggregator.setStats(rawTableName, response, brokerMetrics);
 
     // Report the servers with conflicting data schema.
-    if (!serversWithConflictingDataSchema.isEmpty()) {
+    if (!serversWithConflictingSchema.isEmpty()) {
       String errorMessage = QueryException.MERGE_RESPONSE_ERROR.getMessage() + ": responses for table: " + tableName
-          + " from servers: " + serversWithConflictingDataSchema + " got dropped due to data schema inconsistency.";
+          + " from servers: " + serversWithConflictingSchema + " got dropped due to data schema inconsistency.";
       LOGGER.warn(errorMessage);
       brokerMetrics.addMeteredTableValue(rawTableName, BrokerMeter.RESPONSE_MERGE_EXCEPTIONS, 1);
-      brokerResponseNative.addException(
-          new QueryProcessingException(QueryException.MERGE_RESPONSE_ERROR_CODE, errorMessage));
+      response.addException(new QueryProcessingException(QueryException.MERGE_RESPONSE_ERROR_CODE, errorMessage));
     }
 
     // NOTE: When there is no cached data schema, that means all servers encountered exception. In such case, return the
     //       response with metadata only.
     DataSchema cachedDataSchema =
-        dataSchemaFromNonEmptyDataTable != null ? dataSchemaFromNonEmptyDataTable : dataSchemaFromEmptyDataTable;
+        schemaOfNonEmptyTable != null ? schemaOfNonEmptyTable : schemaOfEmptyTable;
     if (cachedDataSchema == null) {
-      return brokerResponseNative;
+      return response;
     }
 
-    QueryContext serverQueryContext = QueryContextConverterUtils.getQueryContext(serverBrokerRequest.getPinotQuery());
-    DataTableReducer dataTableReducer = ResultReducerFactory.getResultReducer(serverQueryContext);
+    Integer minGroupTrimSizeOpt = null;
+    Integer groupTrimThresholdOpt = null;
+    Integer minInitialIndexedTableCapOpt = null;
 
-    Integer minGroupTrimSizeQueryOption = null;
-    Integer groupTrimThresholdQueryOption = null;
-    Integer minInitialIndexedTableCapacityQueryOption = null;
     if (queryOptions != null) {
-      minGroupTrimSizeQueryOption = QueryOptionsUtils.getMinBrokerGroupTrimSize(queryOptions);
-      groupTrimThresholdQueryOption = QueryOptionsUtils.getGroupTrimThreshold(queryOptions);
-      minInitialIndexedTableCapacityQueryOption = QueryOptionsUtils.getMinInitialIndexedTableCapacity(queryOptions);
+      minGroupTrimSizeOpt = QueryOptionsUtils.getMinBrokerGroupTrimSize(queryOptions);
+      groupTrimThresholdOpt = QueryOptionsUtils.getGroupTrimThreshold(queryOptions);
+      minInitialIndexedTableCapOpt = QueryOptionsUtils.getMinInitialIndexedTableCapacity(queryOptions);
     }
-    int minGroupTrimSize = minGroupTrimSizeQueryOption != null ? minGroupTrimSizeQueryOption : _minGroupTrimSize;
-    int groupTrimThreshold =
-        groupTrimThresholdQueryOption != null ? groupTrimThresholdQueryOption : _groupByTrimThreshold;
+
+    int minGroupTrimSize = minGroupTrimSizeOpt != null ? minGroupTrimSizeOpt : _minGroupTrimSize;
+    int groupTrimThreshold = groupTrimThresholdOpt != null ? groupTrimThresholdOpt : _groupByTrimThreshold;
     int minInitialIndexedTableCapacity =
-        minInitialIndexedTableCapacityQueryOption != null ? minInitialIndexedTableCapacityQueryOption
-            : _minInitialIndexedTableCapacity;
+        minInitialIndexedTableCapOpt != null ? minInitialIndexedTableCapOpt : _minInitialIndexedTableCapacity;
 
+    QueryContext serverQueryContext = QueryContextConverterUtils.getQueryContext(serverBrokerRequest.getPinotQuery());
     try {
-      dataTableReducer.reduceAndSetResults(rawTableName, cachedDataSchema, dataTableMap, brokerResponseNative,
+      DataTableReducer reducer = ResultReducerFactory.getResultReducer(serverQueryContext);
+      reducer.reduceAndSetResults(rawTableName, cachedDataSchema, dataTableMap, response,
           new DataTableReducerContext(_reduceExecutorService, _maxReduceThreadsPerQuery, reduceTimeOutMs,
               groupTrimThreshold, minGroupTrimSize, minInitialIndexedTableCapacity), brokerMetrics);
     } catch (EarlyTerminationException e) {
-      brokerResponseNative.addException(
+      response.addException(
           new QueryProcessingException(QueryException.QUERY_CANCELLATION_ERROR_CODE, e.toString()));
     }
+
     QueryContext queryContext;
     if (brokerRequest == serverBrokerRequest) {
       queryContext = serverQueryContext;
@@ -173,13 +176,13 @@ public BrokerResponseNative reduceOnDataTable(BrokerRequest brokerRequest, Broke
         throw new BadQueryRequestException("Nested query is not supported without gapfill");
       }
       BaseGapfillProcessor gapfillProcessor = GapfillProcessorFactory.getGapfillProcessor(queryContext, gapfillType);
-      gapfillProcessor.process(brokerResponseNative);
+      gapfillProcessor.process(response);
     }
 
     if (!serverQueryContext.isExplain()) {
-      updateAlias(queryContext, brokerResponseNative);
+      updateAlias(queryContext, response);
     }
-    return brokerResponseNative;
+    return response;
   }
 
   public void shutDown() {

pinot-core/src/main/java/org/apache/pinot/core/query/reduce/GroupByDataTableReducer.java

@@ -70,6 +70,7 @@
 
 /**
  * Helper class to reduce data tables and set group by results into the BrokerResponseNative
+ * Used for key-less aggregations, e.g. select max(id), sum(quantity) from orders .
  */
 @SuppressWarnings("rawtypes")
 public class GroupByDataTableReducer implements DataTableReducer {
@@ -140,9 +141,12 @@ public void reduceAndSetResults(String tableName, DataSchema dataSchema,
    * @param brokerMetrics broker metrics (meters)
    * @throws TimeoutException If unable complete within timeout.
    */
-  private void reduceResult(BrokerResponseNative brokerResponseNative, DataSchema dataSchema,
-      Collection<DataTable> dataTables, DataTableReducerContext reducerContext, String rawTableName,
-      BrokerMetrics brokerMetrics)
+  private void reduceResult(BrokerResponseNative brokerResponseNative,
+                            DataSchema dataSchema,
+                            Collection<DataTable> dataTables,
+                            DataTableReducerContext reducerContext,
+                            String rawTableName,
+                            BrokerMetrics brokerMetrics)
       throws TimeoutException {
     // NOTE: This step will modify the data schema and also return final aggregate results.
     IndexedTable indexedTable = getIndexedTable(dataSchema, dataTables, reducerContext);

pinot-core/src/main/java/org/apache/pinot/core/query/request/context/QueryContext.java

@@ -207,7 +207,8 @@ public FilterContext getFilter() {
   }
 
   /**
-   * Returns a list of expressions in the GROUP-BY clause, or {@code null} if there is no GROUP-BY clause.
+   * Returns a list of expressions in the GROUP-BY clause (aggregation keys), or {@code null} if there is no GROUP-BY
+   * clause.
    */
   @Nullable
   public List<ExpressionContext> getGroupByExpressions() {

pinot-core/src/main/java/org/apache/pinot/core/query/request/context/utils/QueryContextConverterUtils.java

@@ -166,12 +166,22 @@ public static QueryContext getQueryContext(PinotQuery pinotQuery) {
       explainMode = ExplainMode.DESCRIPTION;
     }
 
-    return new QueryContext.Builder().setTableName(tableName).setSubquery(subquery)
-        .setSelectExpressions(selectExpressions).setDistinct(distinct).setAliasList(aliasList).setFilter(filter)
-        .setGroupByExpressions(groupByExpressions).setOrderByExpressions(orderByExpressions)
-        .setHavingFilter(havingFilter).setLimit(pinotQuery.getLimit()).setOffset(pinotQuery.getOffset())
-        .setQueryOptions(pinotQuery.getQueryOptions()).setExpressionOverrideHints(expressionContextOverrideHints)
-        .setExplain(explainMode).build();
+    return new QueryContext.Builder()
+        .setTableName(tableName)
+        .setSubquery(subquery)
+        .setSelectExpressions(selectExpressions)
+        .setDistinct(distinct)
+        .setAliasList(aliasList)
+        .setFilter(filter)
+        .setGroupByExpressions(groupByExpressions)
+        .setOrderByExpressions(orderByExpressions)
+        .setHavingFilter(havingFilter)
+        .setLimit(pinotQuery.getLimit())
+        .setOffset(pinotQuery.getOffset())
+        .setQueryOptions(pinotQuery.getQueryOptions())
+        .setExpressionOverrideHints(expressionContextOverrideHints)
+        .setExplain(explainMode)
+        .build();
   }
 
   private static boolean isMultiStage(PinotQuery pinotQuery) {

pinot-core/src/main/java/org/apache/pinot/core/util/GroupByUtils.java

@@ -99,7 +99,8 @@ public static IndexedTable createIndexedTableForCombineOperator(GroupByResultsBl
     int limit = queryContext.getLimit();
     boolean hasOrderBy = queryContext.getOrderByExpressions() != null;
     boolean hasHaving = queryContext.getHavingFilter() != null;
-    int minTrimSize = queryContext.getMinServerGroupTrimSize();
+    int minTrimSize =
+        queryContext.getMinServerGroupTrimSize(); // it's minBrokerGroupTrimSize in broker
     int minInitialIndexedTableCapacity = queryContext.getMinInitialIndexedTableCapacity();
 
     // Disable trim when min trim size is non-positive