presto-orc/src/main/java/io/prestosql/orc/writer/MapColumnWriter.java/MapColumnWriter/getBufferedBytes
class MapColumnWriter:    @Override
    public long getBufferedBytes()
    {
        return lengthStream.getBufferedBytes() + presentStream.getBufferedBytes() + keyWriter.getBufferedBytes() + valueWriter.getBufferedBytes();
    }