milvus插入数据时，明明不超长，但总是报长度错误？

在处理插入milvus数据时，设置了字段长度为512. 明明考虑了预留，插入的数据中没有这么长的，但还是会有报错 类似：MilvusException: (code=0, message=the length (564) of 78th string exceeds max length (512)
查找max(len(x) for x in temp_list)之类  都没有超过512过，也没超过256过，不知道哪里的数据有问题..
反复截段文本等测试后发现，例如用len(x)看到的字符串长度是10，但保存进milus的长度，并不是..

举例，把数据库长度设为一个小值16：
FieldSchema(name="question", dtype=DataType.VARCHAR, auto_id=False, max_length=16)

再把数据缩到只有一行 测试结果插入成功：

line contents is : 你好呀你好 and length is 5
Batches: 100%|█████████████████████████████████████████████████████████████████████████████████████████████████████████████| 1/1 [00:01<00:00,  1.02s/it]
index handle result: Status(code=0, message=)
insert result: (insert count: 1, delete count: 0, upsert count: 0, timestamp: 449735609509740549, success count: 1, err count: 0)

再增加一点文字长度 就报错了：

line contents is : 你好呀你好呀 and length is 6
Batches: 100%|█████████████████████████████████████████████████████████████████████████████████████████████████████████████| 1/1 [00:00<00:00,  1.03it/s]
index handle result: Status(code=0, message=)
[2024-05-13 20:59:27,915 decorators.py:134                              ERROR] RPC error: [batch_insert], <MilvusException: (code=0, message=the length (18) of 0th string exceeds max length (16))>, <Time:{'RPC start': '2024-05-13 20:59:27.912751', 'RPC error': '2024-05-13 20:59:27.915058'}>
Traceback (most recent call last):
  File "/root/temp_dir/run_task.py", line 55, in <module>
    XXX().create_insert_vector_db()
  File "/root/temp_dir/app/service/vector_db/xx_pre_handle.py", line 63, in create_insert_vector_db
    ).get_or_create_db(fields, description, "possible_question_embeddings", entities)
  File "/root/temp_dir/app/service/vector_db/milvus_db.py", line 23, in get_or_create_db
    return self.create_and_insert(fields, description, index_field_name, entities)
  File "/root/temp_dir/app/service/vector_db/milvus_db.py", line 28, in create_and_insert
    self.insert_db(entities)
  File "/root/temp_dir/app/service/vector_db/milvus_db.py", line 40, in insert_db
    insert_result = self.collection.insert(entities)
  File "/root/tmp/venv_dir/1_text_simi/lib/python3.10/site-packages/pymilvus/orm/collection.py", line 497, in insert
    res = conn.batch_insert(
  File "/root/tmp/venv_dir/1_text_simi/lib/python3.10/site-packages/pymilvus/decorators.py", line 135, in handler
    raise e from e
  File "/root/tmp/venv_dir/1_text_simi/lib/python3.10/site-packages/pymilvus/decorators.py", line 131, in handler
    return func(*args, **kwargs)
  File "/root/tmp/venv_dir/1_text_simi/lib/python3.10/site-packages/pymilvus/decorators.py", line 170, in handler
    return func(self, *args, **kwargs)
  File "/root/tmp/venv_dir/1_text_simi/lib/python3.10/site-packages/pymilvus/decorators.py", line 110, in handler
    raise e from e
  File "/root/tmp/venv_dir/1_text_simi/lib/python3.10/site-packages/pymilvus/decorators.py", line 74, in handler
    return func(*args, **kwargs)
  File "/root/tmp/venv_dir/1_text_simi/lib/python3.10/site-packages/pymilvus/client/grpc_handler.py", line 566, in batch_insert
    raise err from err
  File "/root/tmp/venv_dir/1_text_simi/lib/python3.10/site-packages/pymilvus/client/grpc_handler.py", line 560, in batch_insert
    check_status(response.status)
  File "/root/tmp/venv_dir/1_text_simi/lib/python3.10/site-packages/pymilvus/client/utils.py", line 54, in check_status
    raise MilvusException(status.code, status.reason, status.error_code)
pymilvus.exceptions.MilvusException: <MilvusException: (code=0, message=the length (18) of 0th string exceeds max length (16))>

所以，可能是因为UTF-8或其他编码的原因，一些非ASCII字符可能被编码成多个字节 以保存进milvus。
所以，解决方案是 建表时FieldSchema中把max_length 设置为4倍或其他倍数于预期的最大长度。