问题描述：告警日志出现"which is different from the number of indexes 4 defined in the MySQL"报错，如下所示：
数据库：MySQL 5.7.21
1、告警日志
######################################## Error Detail ########################################
230921 21:30:00 [ERROR] Table test/test01 contains 5 indexes inside InnoDB, which is different from the number of indexes 4 defined in the MySQL
230921 21:30:00 [ERROR] Table test/test02 contains 5 indexes inside InnoDB, which is different from the number of indexes 4 defined in the MySQL
说明：出现告警前3分钟有向各表添加索引.
2、异常原因
存储引擎和MySQL服务层中索引信息不一致.
3、测试过程
(root@localhost) [fruitsDB] 17:51:29 4> create table fruitsbak like fruits;
Query OK, 0 rows affected (0.01 sec)
(root@localhost) [fruitsDB] 17:52:11 4> select count(*) from fruitsbak;
+----------+
| count(*) |
+----------+
|        0 |
+----------+
1 row in set (0.01 sec)
(root@localhost) [fruitsDB] 17:54:00 4> \! cp /mysql/data/fruitsDB/fruitsbak.frm /mysql/data/fruitsDB/fruitsbak.frm.old
(root@localhost) [fruitsDB] 17:55:13 4> alter table fruitsbak add index idx_s_id(s_id);
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0
--创建索引后备份.frm文件
(root@localhost) [fruitsDB] 18:09:31 4> \! cp /mysql/data/fruitsDB/fruitsbak.frm /mysql/data/fruitsDB/fruitsbak.frm.old02
[mysql@mysql-leo-master fruitsDB]$ ls -ltr       
total 260
-rw-r-----. 1 mysql mysql     67 Aug 26 12:46 db.opt
-rw-r-----. 1 mysql mysql   8704 Sep 16 22:58 fruits.frm
-rw-r-----. 1 mysql mysql  98304 Sep 16 23:00 fruits.ibd
-rw-r-----. 1 mysql mysql   8704 Sep 23 18:09 fruitsbak.frm.old
-rw-r-----. 1 mysql mysql   8704 Sep 23 18:09 fruitsbak.frm
-rw-r-----. 1 mysql mysql 114688 Sep 23 18:09 fruitsbak.ibd
-rw-r-----. 1 mysql mysql   8704 Sep 23 18:10 fruitsbak.frm.old02
(root@localhost) [fruitsDB] 17:57:31 4> \! mv /mysql/data/fruitsDB/fruitsbak.frm.old /mysql/data/fruitsDB/fruitsbak.frm
[mysql@mysql-leo-master fruitsDB]$ ls -ltr
total 248
-rw-r-----. 1 mysql mysql     67 Aug 26 12:46 db.opt
-rw-r-----. 1 mysql mysql   8704 Sep 16 22:58 fruits.frm
-rw-r-----. 1 mysql mysql  98304 Sep 16 23:00 fruits.ibd
-rw-r-----. 1 mysql mysql   8704 Sep 23 18:09 fruitsbak.frm
-rw-r-----. 1 mysql mysql 114688 Sep 23 18:09 fruitsbak.ibd
-rw-r-----. 1 mysql mysql   8704 Sep 23 18:10 fruitsbak.frm.old02
(root@localhost) [fruitsDB] 17:58:11 4> flush tables;
Query OK, 0 rows affected (0.01 sec)
(root@localhost) [fruitsDB] 17:59:42 4> select s_id from fruitsbak where s_id like '10%' limit 1;
Empty set (0.00 sec)
查看此时错误日志：
2023-09-23T10:00:55.371486Z 6 [Note] Access denied for user 'root'@'localhost' (using password: YES)
2023-09-23T10:01:04.119197Z 7 [ERROR] InnoDB: Table fruitsDB/fruitsbak contains 2 indexes inside InnoDB, which is different from the number of indexes 1 defined in MySQL
2023-09-23T10:03:08.833201Z 4 [ERROR] InnoDB: Table fruitsDB/fruitsbak contains 2 indexes inside InnoDB, which is different from the number of indexes 1 defined in MySQL
说明：此时成功模拟出异常现象.
(root@localhost) [fruitsDB] 18:03:08 4> explain select s_id from fruitsbak where s_id like '10%' limit 1;
+----+-------------+-----------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table     | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-----------+------------+------+---------------+------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | fruitsbak | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    1 |   100.00 | Using where |
+----+-------------+-----------+------------+------+---------------+------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)
说明：此时select语句不会使用索引.
--接着恢复创建索引后的frm文件
(root@localhost) [fruitsDB] 18:12:17 4> \! mv /mysql/data/fruitsDB/fruitsbak.frm.old02 /mysql/data/fruitsDB/fruitsbak.frm
(root@localhost) [fruitsDB] 18:13:55 4> flush tables;
Query OK, 0 rows affected (0.00 sec)
(root@localhost) [fruitsDB] 18:13:59 4> explain select s_id from fruitsbak where s_id like '10%' limit 1;
+----+-------------+-----------+------------+-------+---------------+----------+---------+------+------+----------+--------------------------+
| id | select_type | table     | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra                    |
+----+-------------+-----------+------------+-------+---------------+----------+---------+------+------+----------+--------------------------+
|  1 | SIMPLE      | fruitsbak | NULL       | index | idx_s_id      | idx_s_id | 4       | NULL |    1 |   100.00 | Using where; Using index |
+----+-------------+-----------+------------+-------+---------------+----------+---------+------+------+----------+--------------------------+
1 row in set, 1 warning (0.00 sec)

说明：如上所示，恢复创建索引之后的frm文件，select语句会使用到索引.
(root@localhost) [fruitsDB] 18:14:08 4> alter table fruitsbak engine=innodb;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0
(root@localhost) [fruitsDB] 18:15:38 4> flush tables;
Query OK, 0 rows affected (0.01 sec)
(root@localhost) [fruitsDB] 18:15:46 4> explain select s_id from fruitsbak where s_id like '10%' limit 1;
+----+-------------+-----------+------------+-------+---------------+----------+---------+------+------+----------+--------------------------+
| id | select_type | table     | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra                    |
+----+-------------+-----------+------------+-------+---------------+----------+---------+------+------+----------+--------------------------+
|  1 | SIMPLE      | fruitsbak | NULL       | index | idx_s_id      | idx_s_id | 4       | NULL |    1 |   100.00 | Using where; Using index |
+----+-------------+-----------+------------+-------+---------------+----------+---------+------+------+----------+--------------------------+
1 row in set, 1 warning (0.00 sec)
(root@localhost) [fruitsDB] 18:16:30 4> flush tables;
Query OK, 0 rows affected (0.00 sec)
(root@localhost) [fruitsDB] 18:17:42 4> show create table fruitsbak \G
*************************** 1. row ***************************
       Table: fruitsbak
Create Table: CREATE TABLE `fruitsbak` (
  `f_id` char(10) NOT NULL,
  `s_id` int(11) NOT NULL,
  `f_name` char(255) NOT NULL,
  `f_price` decimal(8,2) NOT NULL,
  `f_attribute` varchar(100) DEFAULT NULL,
  PRIMARY KEY (`f_id`),
  KEY `idx_s_id` (`s_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

1 row in set (0.00 sec)
说明：alter table fruitsbak engine=innodb基于frm的定义重建表.
参考文档：
https://www.percona.com/blog/2011/11/29/innodb-vs-mysql-index-counts/
https://blog.csdn.net/weixin_39789857/article/details/113939652