presto-main/src/main/java/io/prestosql/operator/MergeOperator.java/MergeOperatorFactory/createOperator
class MergeOperatorFactory:        @Override
        public SourceOperator createOperator(DriverContext driverContext)
        {
            checkState(!closed, "Factory is already closed");
            OperatorContext operatorContext = driverContext.addOperatorContext(operatorId, sourceId, MergeOperator.class.getSimpleName());

            return new MergeOperator(
                    operatorContext,
                    sourceId,
                    exchangeClientSupplier,
                    serdeFactory.createPagesSerde(),
                    orderingCompiler.compilePageWithPositionComparator(types, sortChannels, sortOrder),
                    outputChannels,
                    outputTypes);
        }