presto-main/src/main/java/io/prestosql/sql/planner/iterative/Memo.java/Memo/storeStats
class Memo:    public void storeStats(int groupId, PlanNodeStatsEstimate stats)
    {
        Group group = getGroup(groupId);
        if (group.stats != null) {
            evictStatisticsAndCost(group); // cost is derived from stats, also needs eviction
        }
        group.stats = requireNonNull(stats, "stats is null");
    }