mysql> show variables like '%innodb_force_recovery%';

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

| Variable_name | Value |

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

| innodb_force_recovery | 0 |

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

该参数默认值为0，代表当发生需要恢复时，机型所有的恢复操作，当不能进行有效恢复时，如数据页发生了corruption，MySQL数据库可能法师宕机(crash)，并把错误写入错误日志中。

该参数还可以设置为6个非零的值：1-6。大的数字表示包含了前面所有小数字表示的影响

1 srv_force_ignore_corrupt: 忽律检查到corrupt页

2 srv_force_no_background: 阻止Master Thread线程的运行，如Master Thread线程需要进行full purge操作，而这会导致crash。

3 srv_force_no_trx_undo: 不进行事务的回滚操作

4 srv_force_no_ibuf_merge: 不进行插入缓冲的合并操作

5 srv_force_no_undo_log_scan: 不查看撤销日志(undo log),InnoDB存储引擎会将未提交的事务视为已提交

6 srv_force_no_log_redo 不进行前滚操作

注意：

当参数innodb_force_recovery设置大于0的值，用户可以对表进行select,create和drop操作，但insert\update\delete这类DML操作是不允许的。

模拟故障

Database changed

mysql> start transaction

-> ;

Query OK, 0 rows affected (0.00 sec)

mysql> update t4 set VERSION=1;

Query OK, 581632 rows affected (11.40 sec)

Rows matched: 581632 Changed: 581632 Warnings: 0

[root@mysql5-7 ~]# ps aux | grep mysql

root 3928 0.0 0.0 106244 1448 pts/1 S 14:55 0:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/data/3306/my.cnf

root 4585 0.0 0.1 126688 3012 pts/1 S+ 14:55 0:00 mysql -uroot -px xxxx -S /data/3306/soket/mysql.sock

mysql 4624 10.3 21.7 2269864 417796 pts/1 Sl 14:57 0:18 /usr/local/mysql/bin/mysqld --defaults-file=/data/3306/my.cnf --basedir=/usr/local/mysql --datadir=/data/3306/data --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=/data/3306/logs/mysql_ray.err --open-files-limit=10240 --pid-file=/data/3306/logs/ray.pid --socket=/data/3306/soket/mysql.sock --port=3306

root 5884 0.0 0.0 100952 612 pts/2 S+ 15:00 0:00 tail -f /data/3306/logs/mysql_ray.err

root 5889 0.0 0.0 103260 832 pts/3 S+ 15:00 0:00 grep mysql

[root@mysql5-7 ~]# kill -9 3928

[root@mysql5-7 ~]# kill -9 4624

[root@mysql5-7 ~]# ps aux | grep mysql

root 4585 0.0 0.1 126688 3012 pts/1 S+ 14:55 0:00 mysql -uroot -px xxxx -S /data/3306/soket/mysql.sock

root 5884 0.0 0.0 100952 612 pts/2 S+ 15:00 0:00 tail -f /data/3306/logs/mysql_ray.err

root 5895 0.0 0.0 103260 836 pts/3 S+ 15:00 0:00 grep mysql

2017-05-25T07:01:10.663268Z 0 [Note] InnoDB: Database was not shutdown normally!

2017-05-25T07:01:10.663287Z 0 [Note] InnoDB: Starting crash recovery.

2017-05-25T07:01:10.695649Z 0 [Note] InnoDB: 1 transaction(s) which must be rolled back or cleaned up in total 581632 row operations to undo

2017-05-25T07:01:10.695733Z 0 [Note] InnoDB: Trx id counter is 5888

2017-05-25T07:01:10.700667Z 0 [Note] InnoDB: Last MySQL binlog file position 0 62744449, file name ray-bin.000007

2017-05-25T07:01:10.806383Z 0 [Note] InnoDB: Removed temporary tablespace data file: "ibtmp1"

2017-05-25T07:01:10.806472Z 0 [Note] InnoDB: Creating shared tablespace for temporary tables

这里看到 581632 row operations to undo，因为回滚了数据，所以启动时间会加长，如果回滚数据非常多，启动时间就会很慢。

重新做一次实验，innodb_force_recovery设置为3.

[root@mysql5-7 ~]# ps aux | grep mysql

root 4585 0.0 0.1 126640 3004 pts/1 S+ 14:55 0:00 mysql -uroot -px xxxx -S /data/3306/soket/mysql.sock

root 5884 0.0 0.0 100952 612 pts/2 S+ 15:00 0:00 tail -f /data/3306/logs/mysql_ray.err

root 5916 0.0 0.0 106244 1456 pts/3 S 15:01 0:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/data/3306/my.cnf

mysql 6546 7.3 21.7 2269272 417740 pts/3 Sl 15:01 0:19 /usr/local/mysql/bin/mysqld --defaults-file=/data/3306/my.cnf --basedir=/usr/local/mysql --datadir=/data/3306/data --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=/data/3306/logs/mysql_ray.err --open-files-limit=10240 --pid-file=/data/3306/logs/ray.pid --socket=/data/3306/soket/mysql.sock --port=3306

root 6586 0.0 0.0 103260 836 pts/3 S+ 15:05 0:00 grep mysql

[root@mysql5-7 ~]# kill -9 5916

[root@mysql5-7 ~]# kill -9 6546

[root@mysql5-7 ~]# ps aux | grep mysql

root 4585 0.0 0.1 126640 3004 pts/1 S+ 14:55 0:00 mysql -uroot -px xxxx -S /data/3306/soket/mysql.sock

root 5884 0.0 0.0 100952 612 pts/2 S+ 15:00 0:00 tail -f /data/3306/logs/mysql_ray.err

root 5916 0.0 0.0 106244 1456 pts/3 S 15:01 0:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/data/3306/my.cnf

mysql 6546 7.3 21.7 2269272 417740 pts/3 Sl 15:01 0:19 /usr/local/mysql/bin/mysqld --defaults-file=/data/3306/my.cnf --basedir=/usr/local/mysql --datadir=/data/3306/data --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=/data/3306/logs/mysql_ray.err --open-files-limit=10240 --pid-file=/data/3306/logs/ray.pid --socket=/data/3306/soket/mysql.sock --port=3306

root 6586 0.0 0.0 103260 836 pts/3 S+ 15:05 0:00 grep mysql

[root@mysql5-7 ~]# kill -9 5916

[root@mysql5-7 ~]# kill -9 6546

2017-05-25T07:06:05.298605Z 0 [Note] InnoDB: 32 non-redo rollback segment(s) are active.

2017-05-25T07:06:05.299344Z 0 [Note] InnoDB: 5.7.10 started; log sequence number 805301564

2017-05-25T07:06:05.299424Z 0 [Note] InnoDB: !!! innodb_force_recovery is set to 3 !!!

2017-05-25T07:06:05.300353Z 0 [Note] Plugin 'FEDERATED' is disabled.

2017-05-25T07:06:05.302471Z 0 [Note] Recovering after a crash using /data/3306/logs/ray-bin

2017-05-25T07:06:05.302981Z 0 [Note] InnoDB: Loading buffer pool(s) from /data/3306/data/ib_buffer_pool

2017-05-25T07:06:05.303049Z 0 [Note] InnoDB: not started

2017-05-25T07:06:05.305844Z 0 [Note] Starting crash recovery...

2017-05-25T07:06:05.305926Z 0 [Note] Crash recovery finished.

因为没有进行回滚，所以启动很快就完成了。但是用户应当小心当前数据库的状态，并自己确认是否不需要回滚事务的操作。

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innodb_force_recovery设置

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