presto-main/src/main/java/io/prestosql/sql/planner/iterative/Memo.java/Memo/evictStatisticsAndCost
class Memo:    private void evictStatisticsAndCost(Group group)
    {
        group.stats = null;
        group.cost = null;
        for (int parentGroup : group.incomingReferences.elementSet()) {
            if (parentGroup != ROOT_GROUP_REF) {
                evictStatisticsAndCost(getGroup(parentGroup));
            }
        }
    }