public boolean needDeepResultCollection() {
        if (forceSinglePass) {
            return true;
        }
        for (GroupingLevel level : groupingLevels) {
            if (level.needResultCollection()) {
                return true;
            }
        }
        return false;
    }
Returns whether ordering will need results collected in children.
In that case we will probably just do a single pass.
searchlib/src/main/java/com/yahoo/searchlib/aggregation/Grouping.java