@Override
    public ConvertedRecords<MemoryRecords> downConvert(byte toMagic, long firstOffset, Time time) {
        return RecordsUtil.downConvert(batches(), toMagic, firstOffset, time);
    }
The total number of bytes in this message set not including any partial, trailing messages. This
may be smaller than what is returned by {@link #sizeInBytes()}.
@return The number of valid bytes
clients/src/main/java/org/apache/kafka/common/record/MemoryRecords.java