presto-parquet/src/main/java/io/prestosql/parquet/reader/PrimitiveColumnReader.java/PrimitiveColumnReader/createDecimalColumnReader
class PrimitiveColumnReader:    private static Optional<PrimitiveColumnReader> createDecimalColumnReader(RichColumnDescriptor descriptor)
    {
        Optional<Type> type = createDecimalType(descriptor);
        if (type.isPresent()) {
            DecimalType decimalType = (DecimalType) type.get();
            return Optional.of(DecimalColumnReaderFactory.createReader(descriptor, decimalType.getPrecision(), decimalType.getScale()));
        }
        return Optional.empty();
    }