presto-main/src/main/java/io/prestosql/sql/planner/planprinter/OperatorHashCollisionsStats.java/OperatorHashCollisionsStats/merge
class OperatorHashCollisionsStats:    public static OperatorHashCollisionsStats merge(OperatorHashCollisionsStats first, OperatorHashCollisionsStats second)
    {
        return new OperatorHashCollisionsStats(
                first.weightedHashCollisions + second.weightedHashCollisions,
                first.weightedSumSquaredHashCollisions + second.weightedSumSquaredHashCollisions,
                first.weightedExpectedHashCollisions + second.weightedExpectedHashCollisions);
    }