presto-orc/src/main/java/io/prestosql/orc/writer/StructColumnWriter.java/StructColumnWriter/getBufferedBytes
class StructColumnWriter:    @Override
    public long getBufferedBytes()
    {
        long bufferedBytes = presentStream.getBufferedBytes();
        for (ColumnWriter structField : structFields) {
            bufferedBytes += structField.getBufferedBytes();
        }
        return bufferedBytes;
    }