presto-orc/src/main/java/io/prestosql/orc/reader/DecimalColumnReader.java/DecimalColumnReader/openRowGroup
class DecimalColumnReader:    private void openRowGroup()
            throws IOException
    {
        presentStream = presentStreamSource.openStream();
        decimalStream = decimalStreamSource.openStream();
        scaleStream = scaleStreamSource.openStream();
        rowGroupOpen = true;
    }