presto-main/src/main/java/io/prestosql/operator/PartitionedOutputOperator.java/PartitionedOutputOperator/mergeWith
class PartitionedOutputOperator:        @Override
        public PartitionedOutputInfo mergeWith(PartitionedOutputInfo other)
        {
            return new PartitionedOutputInfo(
                    rowsAdded + other.rowsAdded,
                    pagesAdded + other.pagesAdded,
                    Math.max(outputBufferPeakMemoryUsage, other.outputBufferPeakMemoryUsage));
        }