public int getCapacity() {
    return groupByHash.getCapacity();
  }
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