mysql更新varchar类型字段长度报错：ERROR 1074 (42000): Column length too big for column ‘value‘ (max = 21845)；

mysql> alter table `apm_heuristic_result`
    -> modify column  `value` varchar(65535)  not null comment 'value';
ERROR 1074 (42000): Column length too big for column 'value' (max = 21845); use BLOB or TEXT instead

mysql> alter table `apm_heuristic_result` modify column  `value` varchar(21000)  not null comment 'value';
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> alter table `apm_heuristic_result` modify column  `value` varchar(21730)  not null comment 'value';
ERROR 1118 (42000): Row size too large. The maximum row size for the used table type, not counting BLOBs, is 65535. This includes storage overhead, check the manual. You have to change some columns to TEXT or BLOBs