private Iterator<Integer> consecutiveGroupIds() {
    if (groupIds == null) {
      groupIds = IntStream.range(0, groupByHash.getGroupCount()).iterator();
    }
    return groupIds;
  }
building hash sorted results requires memory for sorting group IDs. This method returns size of
that memory requirement.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/relational/aggregation/grouped/builder/InMemoryHashAggregationBuilder.java