监控到一台MySQL实例在早上发生过Crash，上去看了一下，已经被mysqld_safe成功拉起。
上去检查一下错误日志，发现错误日志如下（已对表名，库名，路径做脱敏处理）：

……………………………………（大量相同的报错）…………………………………………

2017-08-31T11:11:04.291424Z 32394522 [ERROR] InnoDB: Record in index `t_idx` of table `$db_name`.`$tb_name` was not found on update: TUPLE (info_bits=0, 9 fields): {[12]121098369601(0x010201000908030609060001),[9] (0x000000000000010000),[4]KOWA(0x0B0F0701),[4]AYNA(0x01090E01),[6]STAT44(0x030401040404),[4]AYNA(0x01090E01),[1]0(0x00),[1]0(0x00),[32]8f2a39b44fe74cd781527d856342d834(0x0806020103090204040605070403040708010502070408050603040204080304)} at: COMPACT RECORD(info_bits=0, 9 fields): {[12]121098369601(0x010201000908030609060001),[9] (0x000000000000010000),[4]KOWA(0x0B0F0701),[4]AYNA(0x01090E01),NULL,NULL,[1]0(0x00),[1]0(0x00),[32]8f2a39b44fe74cd781527d856342d834(0x0806020103090204040605070403040708010502070408050603040204080304)}

2017-08-31T03:11:04.291454Z 32394522 [Note] InnoDB: GIS MBR INFO: 1.31506e-47 and 1.02964e-71, 2.8816e-306, 1.93059e+53

2017-08-31 03:11:04 0x7fcaf04be700 InnoDB: Assertion failure in thread 140509591627520 in file row0ins.cc line 282

InnoDB: Failing assertion: !cursor->index->is_committed()

InnoDB: We intentionally generate a memory trap.

InnoDB: Submit a detailed bug report to http://bugs.mysql.com.

InnoDB: If you get repeated assertion failures or crashes, even

InnoDB: immediately after the mysqld startup, there may be

InnoDB: corruption in the InnoDB tablespace. Please refer to

InnoDB: http://dev.mysql.com/doc/refman/5.7/en/forcing-innodb-recovery.html

InnoDB: about forcing recovery.

03:11:04 UTC - mysqld got signal 6 ;

This could be because you hit a bug. It is also possible that this binary

or one of the libraries it was linked against is corrupt, improperly built,

or misconfigured. This error can also be caused by malfunctioning hardware.

Attempting to collect some information that could help diagnose the problem.

As this is a crash and something is definitely wrong, the information

collection process might fail.

…………………………………………………………………………………………………………

Trying to get some variables.

Some pointers may be invalid and cause the dump to abort.

Query (7fca7c0dbaa0): is an invalid pointer

Connection ID (thread ID): 32394522

Status: NOT_KILLED

The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains

information that should help you find out what is causing the crash.

…………………………………………………………………………………………………………

（重启中）

…………………………………………………………………………………………………………

2017-08-31T03:11:08.925622Z 0 [Note] $basedir/bin/mysqld: ready for connections.

Version: '5.7.12-log' socket: '$datadir/mysqld.sock' port: 3306 Source distribution

2017-08-31T03:31:10.232145Z 1704 [ERROR] InnoDB: Record in index `t_idx` of table `$db_name`.`$tb_name` was not found on update: TUPLE (info_bits=0, 9 fields): {[12]198051077411(0x010908000501000707040101),[9] 7 (0x000000000000020700),[4]AOGA(0x010F0701),[4]AQGA(0x01010701),[6]STAT44(0x030401040404),NULL,[1]0(0x00),[1]0(0x00),[32]c6f98a358ace4897a11a27d689bb6884(0x0306060908010305080103050408090701010101020704060809020206080804)} at: COMPACT RECORD(info_bits=0, 9 fields): {[12]198051077411(0x010908000501000707040101),[9] 7 (0x000000000000020700),[4]AOGA(0x010F0701),[4]AQGA(0x01010701),NULL,NULL,[1]0(0x00),[1]0(0x00),[32]c6f98a358ace4897a11a27d689bb6884(0x0306060908010305080103050408090701010101020704060809020206080804)}

2017-08-31T03:31:10.232168Z 1704 [Note] InnoDB: GIS MBR INFO: 7.26084e-43 and 1.08604e-42, 2.8823e-306, 132832

2017-08-31T03:35:51.201716Z 2208 [ERROR] InnoDB: Flagged corruption of `t_idx` in table `$db_name`.`$tb_name` in CHECK TABLE; Wrong count

初步确定为因为名为t_idx的索引损坏导致的大量报错，并在处理update语句时导致crash。
检查binlog发现的确有很多对该表的update操作。
执行一下check table，发现的确有问题：

mysql> CHECK TABLE `$db_name`.`$tb_name`;

+--------------------+-------+----------+-------------------------------------------------------+

| Table | Op| Msg_type | Msg_text |

+--------------------+-------+----------+-------------------------------------------------------+

| $db_name.$tb_name | check | Warning | InnoDB: Index t_idx is marked as corrupted|

| $db_name.$tb_name | check | error| Corrupt|

+--------------------+-------+----------+-------------------------------------------------------+

2 rows in set (0.83 sec)

因该库为高可用主库，检查到备库状态正常，准备先手动做failover，再对该表进行修复。

因为表小，也比较幸运，修复过程十分顺利：

mysql> OPTIMIZE TABLE `$db_name`.`$tb_name`;

+--------------------+----------+----------+-------------------------------------------------------------------+

| Table | Op| Msg_type | Msg_text |

+--------------------+----------+----------+-------------------------------------------------------------------+

| $db_name.$tb_name | optimize | note| Table does not support optimize, doing recreate + analyze instead |

| $db_name.$tb_name | optimize | status | OK |

+--------------------+----------+----------+-------------------------------------------------------------------+

2 rows in set (3.42 sec)

mysql> ALTER TABLE `$db_name`.`$tb_name` ENGINE=INNODB;

Query OK, 0 rows affected (3.09 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> ANALYZE TABLE `$db_name`.`$tb_name`;

+--------------------+---------+----------+----------+

| Table | Op | Msg_type | Msg_text |

+--------------------+---------+----------+----------+

| $db_name.$tb_name| analyze | status| OK |

+--------------------+---------+----------+----------+

1 row in set (0.00 sec)

mysql> CHECK TABLE `$db_name`.`$tb_name`;

+--------------------+-------+----------+----------+

| Table | Op | Msg_type | Msg_text |

+--------------------+-------+----------+----------+

| $db_name.$tb_name| check | status| OK |

+--------------------+-------+----------+----------+

1 row in set (0.98 sec)