梳理下MySQL崩溃恢复过程

基于MySQL5.7版本，5.7版本在恢复过程做了优化，本文描述不考虑之前版本。

1 初始化崩溃恢复

    数据库关闭只有2种情况，正常关闭，非正常关闭（包括数据库实例crash及服务器crash）。

    正常关闭情况，所有buffer pool里边的脏页都会都会刷新一遍到磁盘，同时记录最新LSN到ibdata文件的第一个page中。而非正常关闭来不及做这些操作，也就是没及时把脏数据flush到磁盘，也没有记录最新LSN到ibdata file。

    当我们重启数据库实例的时候，数据库做2个阶段性操作：redo log处理，undo log及binlog 处理。

1.1 redo log处理

• 打开系统表空间ibdata，读取第一个page中的LSN，若第一个页损坏，则依次往后面的page读，知道有个完整的page能够提供LSN，这个LSN当作上次shutdown时的checkpoint点，后续恢复，从这个LSN点开始恢复

• 进入redo log文件，读取第一个redo log文件头的checkpoint LSN， 并根据该LSN定位到redo日志文件中对应的位置，从该checkpoint点开始扫描，进行3次redo log文件扫描：

• • 第一次，找 MLOG_CHECKPOINT日志

• • • 如果是正常关闭，这个日志是不做记录的，也就是扫描的过程中不回找到对应的MLOG_CHECKPOINT日志，不会进行接下来的两次扫描，因为属于正常关闭数据库服务，不需要考虑奔溃恢复情况；

• • • 如果是非正常关闭，则会查找到 MLOG_CHECKPOINT （如果是多个，则说明redo文件已损坏，恢复报错），获取MLOG_FILE_NAME中指定后续需要恢复的ibd文件；

• • 第二次，从redo log读到的LSN，找到checkpoint点开始重复扫描存储日志对象

• • • 根据MLOG_CHECKPOINT日志，读取对应LSN之后的日志解析到hash表中，如果剩下的日志解析结束后还没有填满hash表格，则不需要进行第三次扫描；

• • • 进行到这里，则说明数据库是非正常关闭，会在errorlog中提示：Database was not shutdown normally!详见下图。

• • • 

• • 第三次，若第二次扫描hash表空间不足，则发起第三次扫描，清空hash表空间，重新从新的checkpoint点开始扫描

• • • 如果第二次扫扫描就把hash表填满，那么会先把hash表里边的记录重做到buffer pool中的数据页，然后再来加载redo log 记录到被清空的hash表中，hash表满后立即执行恢复操作，知道所有需要redo 的redo log 被应用结束。

    恢复的过程中，注意两个点：打开ibd文件形式，读取数据库到buffer pool的改进。

    根据hash表中的相应信息读取数据页， 读数据页的时候，5.7之前版本采用把所有表空间都打开，所有表格仅执行ReadOnly，5.7版本做了优化，新增了 MLOG_FILE_NAME 记录在checkpoint之后，所有被修改过的信息，根据这些信息，在恢复过程中，只需要打开相应的ibd文件即可，不涉及恢复的表格支持正常DML跟DDL操作，涉及恢复的表格则仅执行ReadOnly功能。

    当把数据页读取到buffer pool中，以往版本是只读取对应的单个页面，而现在的是直接读取与该页面相邻的32个data page 也一起加载的buffer pool，因为一个数据页的修改，可能周围的页面也被修改，一次性读取，可以避免后面根据hash表中再重新读取其相邻的页面。

1.2 undo log及binlog 处理

      上一阶段中，把redo log中的操作都apply到数据页中，但是对于prepare状态的事务却还没有进行回滚处理，这个阶段则是针对prepare状态的事务进行处理，需要使用到binlog和undo log。

• 根据最后一个binlog文件，为啥不是所有binlog文件呢？因为每一个binlog文件切换的时候，都会确保当前binlog文件的所有操作已落盘，所以只需要考虑最后一个binlog文件。跟进最后一个binlog文件，获取所有可能没有提交事务的xid列表；

• 根据undo log中的 insert_undo_list，upddate_undo_list事务链，构建undo_list，在根据undo_list构建未提交事务链表;

• 从未提交事务链表中，提取出xid，凡是存在于xid列表中的，则需要提交，不存在的，则回滚。

      整个恢复过程，可以参考下来自 www.sysdb.cn 网站作者  boyce 画的说明图，图片版权属于该作者，本处仅为引用分享给大家，作图很详细，一言不合开源码分析！遗憾的是，作者只写了2篇博文就停止更新了，心疼默哀十分钟.....

2 innodb关闭恢复涉及参数

2.1 关闭参数：innodb_fast_shutdown

    数据库关闭的时候，innodb需要完成所有full purge何insert buffer操作，这需要一些时间，甚至几个小时完成

• 0
  • 关闭时，需要完成所有full purge，insert buffer， flush dirty pages操作
  • 做 innodb plugin升级时，会设置为0，再正常关闭数据库。
• 1
  • 默认值，表示不需要完成full purge和insert buffer操作，但是缓冲池的脏数据需要刷新到磁盘
• 2
  • 既不完成full purge和insert buffer操作，也不把缓冲池的脏数据刷新到磁盘，而是将日志写入日志文件，这样不回有数据丢失，但是下次mysql启动的时候，需要根据日志文件执行恢复操作

2.2 恢复参数：innodb_force_recovery

    这里注意，数字越小，则忽略检查的内容越少，每个大的数字都包含了前面小数字忽略检查的内容。当参数设置大于0后，可以对表格进行DML操作，但是DDL操作时不允许的。

    当innodb_force_recovery 值为1-3时，仅允许SELECT TABLE ，DROP or CREATE tables；innodb_force_recovery 值为>=4时，5.7.17之前版本支持DROP TABLE，5.7.18后版本不支持。

    参数说明如下图：

3 测试情况

    测试内容：

    begin;insert into orders select * from orders.orders limit 100000;

    插入结束后不提交事务，执行 kill mysql进程

    tailf error.log查看

3.1 默认配置测试：innodb_fast_shutdown=1，innodb_force_recovery=0

   配置说明：异常停止DB服务时，不需要完成 full purge 和 insert buffer 操作，但是缓冲池的脏数据需要刷新到磁盘；服务启动的时候，做所有需要的检查跟事务操作。

3.1.1 操作过程

#1 tailf error.log查看mysql错误日志,动态滚动查看
mysql> show global variables like 'log_error';
tailf /data/mysql/mysql3310/data/error.log

#2 测试库中开启事务，insert 10w行记录，不提交事务
mysql> begin;insert into orders select * from orders.orders limit 100000;
Query OK, 0 rows affected (0.00 sec)

Query OK, 100000 rows affected (37.55 sec)
Records: 100000  Duplicates: 0  Warnings: 0

#3 查找mysql进程号，杀进程
[root@localhost opt]# ps axu | grep mysql
[root@localhost opt]# kill -9 mysql的进程号

#4 启动mysql服务
mysqld --defaults-file=/data/mysql/mysql3310/mysql3310.cnf &

#5 到tailf error.log窗口查看错误

3.1.2 error log解析

启动mysqld进程

2017-03-16T16:28:13.812074Z 0 [Note] mysqld (mysqld 5.7.14-log) starting as process 28091 ...

 

读取ibdata的LSN

读取redo文件的checkpoint，从该点的LSN开始查找MLOG_CHECKPOINT

发现MLOG_CHECKPOINT日志，提示：Database was not shutdown normally !  

2017-03-16T16:28:16.572276Z 0 [Note] InnoDB: Log scan progressed past the checkpoint lsn 898634772645

2017-03-16T16:28:16.572418Z 0 [Note] InnoDB: Doing recovery: scanned up to log sequence number 898634772654

2017-03-16T16:28:16.693771Z 0 [Note] InnoDB: Doing recovery: scanned up to log sequence number 898634772654

2017-03-16T16:28:16.693880Z 0 [Note] InnoDB: Database was not shutdown normally!

2017-03-16T16:28:16.693913Z 0 [Note] InnoDB: Starting crash recovery.

 

检测需要重做跟回滚的事务

由于没有需要redo的事务，但是有undo事务，开始undo操作

加载redo log中的96个系统回滚段 rollbak segment，32个不需要redo 的临时表空间的回滚段

2017-03-16T16:28:17.360953Z 0 [Note] InnoDB: 1 transaction(s) which must be rolled back or cleaned up in total 100000 row operations to undo

 

获取binlog回滚xid列表，结合undo log做回滚操作

2017-03-16T16:28:17.361122Z 0 [Note] InnoDB: Trx id counter is 5716480

2017-03-16T16:28:17.625441Z 0 [Note] InnoDB: Last MySQL binlog file position 0 37774, file name bin_log.000016

2017-03-16T16:28:17.787684Z 0 [Note] InnoDB: Starting in background the rollback of uncommitted transactions

2017-03-16T16:28:17.788022Z 0 [Note] InnoDB: Rolling back trx with id 5715975, 100000 rows to undo

 

启动innodb，加载buffer pool

2017-03-16T16:28:17.838323Z 0 [Note] InnoDB: Waiting for purge to start

2017-03-16T16:28:18.015792Z 0 [Note] InnoDB: 5.7.14 started; log sequence number 898634772654

 

mysqld正常运行提供用户使用

2017-03-16T16:28:18.772035Z 0 [Note] mysqld: ready for connections.

Version: '5.7.14-log'  socket: '/tmp/mysql3310.sock'  port: 3310  MySQL Community Server (GPL)

 

这个时候，recovery可能还没结束，比如这个例子中，recovery就还在进行，其涉及的表仅提供ReadOnly操作，其他表格可正常操作 ，慢慢恢复，最后undo回滚事务完成，Rollback of non-prepared transactions completed

 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 1002017-03-16T16:29:24.353056Z 0 [Note] InnoDB: Rollback of trx with id 5715975 completed

2017-03-16T16:29:24.353267Z 0 [Note] InnoDB: Rollback of non-prepared transactions completed

 

整个过程16:28:13启动，16:28:18 DB提供部分服务，16:29:24全库恢复，db部分提供服务耗时5s，全库提供服务耗时71s 。

2017-03-16T16:28:13.812074Z 0 [Note] mysqld (mysqld 5.7.14-log) starting as process 28091 ...
2017-03-16T16:28:14.250956Z 0 [Note] InnoDB: PUNCH HOLE support not available
2017-03-16T16:28:14.251212Z 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2017-03-16T16:28:14.251311Z 0 [Note] InnoDB: Uses event mutexes
2017-03-16T16:28:14.251359Z 0 [Note] InnoDB: GCC builtin __sync_synchronize() is used for memory barrier
2017-03-16T16:28:14.251401Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.3
2017-03-16T16:28:14.251311Z 0 [Note] InnoDB: Uses event mutexes
2017-03-16T16:28:14.251359Z 0 [Note] InnoDB: GCC builtin __sync_synchronize() is used for memory barrier
2017-03-16T16:28:14.251401Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.3
2017-03-16T16:28:14.251440Z 0 [Note] InnoDB: Using Linux native AIO
2017-03-16T16:28:14.252570Z 0 [Note] InnoDB: Number of pools: 1
2017-03-16T16:28:14.253079Z 0 [Note] InnoDB: Not using CPU crc32 instructions
2017-03-16T16:28:14.258163Z 0 [Note] InnoDB: Initializing buffer pool, total size = 9G, instances = 8, chunk size = 128M
2017-03-16T16:28:16.101862Z 0 [Note] InnoDB: Completed initialization of buffer pool
2017-03-16T16:28:16.406890Z 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().
2017-03-16T16:28:16.447145Z 0 [Note] InnoDB: Highest supported file format is Barracuda.
2017-03-16T16:28:16.572276Z 0 [Note] InnoDB: Log scan progressed past the checkpoint lsn 898634772645
2017-03-16T16:28:16.572418Z 0 [Note] InnoDB: Doing recovery: scanned up to log sequence number 898634772654
2017-03-16T16:28:16.693771Z 0 [Note] InnoDB: Doing recovery: scanned up to log sequence number 898634772654
2017-03-16T16:28:16.693880Z 0 [Note] InnoDB: Database was not shutdown normally!
2017-03-16T16:28:16.693913Z 0 [Note] InnoDB: Starting crash recovery.
2017-03-16T16:28:17.360953Z 0 [Note] InnoDB: 1 transaction(s) which must be rolled back or cleaned up in total 100000 row operations to undo
2017-03-16T16:28:17.361122Z 0 [Note] InnoDB: Trx id counter is 5716480
2017-03-16T16:28:17.625441Z 0 [Note] InnoDB: Last MySQL binlog file position 0 37774, file name bin_log.000016
2017-03-16T16:28:17.787684Z 0 [Note] InnoDB: Starting in background the rollback of uncommitted transactions
2017-03-16T16:28:17.788022Z 0 [Note] InnoDB: Rolling back trx with id 5715975, 100000 rows to undo

InnoDB: Progress in percents: 12017-03-16T16:28:17.788272Z 0 [Note] InnoDB: Removed temporary tablespace data file: "ibtmp1"
2017-03-16T16:28:17.788603Z 0 [Note] InnoDB: Creating shared tablespace for temporary tables
2017-03-16T16:28:17.788603Z 0 [Note] InnoDB: Creating shared tablespace for temporary tables
2017-03-16T16:28:17.788937Z 0 [Note] InnoDB: Setting file './ibtmp1' size to 12 MB. Physically writing the file full; Please wait ...
2017-03-16T16:28:17.831078Z 0 [Note] InnoDB: File './ibtmp1' size is now 12 MB.
2017-03-16T16:28:17.834673Z 0 [Note] InnoDB: 96 redo rollback segment(s) found. 96 redo rollback segment(s) are active.
2017-03-16T16:28:17.834822Z 0 [Note] InnoDB: 32 non-redo rollback segment(s) are active.
2017-03-16T16:28:17.838323Z 0 [Note] InnoDB: Waiting for purge to start
2017-03-16T16:28:18.015792Z 0 [Note] InnoDB: 5.7.14 started; log sequence number 898634772654
2017-03-16T16:28:18.018091Z 0 [Note] InnoDB: Loading buffer pool(s) from /data/mysql/mysql3310/data/ib_buffer_pool
2017-03-16T16:28:18.018464Z 0 [Note] Plugin 'FEDERATED' is disabled.
2017-03-16T16:28:18.119301Z 0 [Note] Recovering after a crash using /data/mysql/mysql3310/logs/bin_log
2017-03-16T16:28:18.119442Z 0 [Note] Starting crash recovery...
2017-03-16T16:28:18.119442Z 0 [Note] Starting crash recovery...
2017-03-16T16:28:18.119624Z 0 [Note] Crash recovery finished.
2017-03-16T16:28:18.203723Z 0 [Warning] Failed to set up SSL because of the following SSL library error: SSL context is not usable without certificate and private key
2017-03-16T16:28:18.203835Z 0 [Note] Server hostname (bind-address): '*'; port: 3310
2017-03-16T16:28:18.204188Z 0 [Note] IPv6 is available.
2017-03-16T16:28:18.204339Z 0 [Note]   - '::' resolves to '::';
2017-03-16T16:28:18.204667Z 0 [Note] Server socket created on IP: '::'.
2017-03-16T16:28:18.377789Z 0 [Warning] 'user' entry 'mysql.sys@localhost' ignored in --skip-name-resolve mode.
2017-03-16T16:28:18.378054Z 0 [Warning] 'db' entry 'sys mysql.sys@localhost' ignored in --skip-name-resolve mode.
2017-03-16T16:28:18.378170Z 0 [Warning] 'proxies_priv' entry '@ root@localhost' ignored in --skip-name-resolve mode.
2017-03-16T16:28:18.392680Z 0 [Warning] 'tables_priv' entry 'sys_config mysql.sys@localhost' ignored in --skip-name-resolve mode.
2017-03-16T16:28:18.771122Z 0 [Note] Event Scheduler: Loaded 0 events
2017-03-16T16:28:18.772035Z 0 [Note] mysqld: ready for connections.
Version: '5.7.14-log'  socket: '/tmp/mysql3310.sock'  port: 3310  MySQL Community Server (GPL)
2017-03-16T16:28:21.404135Z 0 [Note] InnoDB: Buffer pool(s) load completed at 170317  0:28:21
 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 1002017-03-16T16:29:24.353056Z 0 [Note] InnoDB: Rollback of trx with id 5715975 completed
2017-03-16T16:29:24.353267Z 0 [Note] InnoDB: Rollback of non-prepared transactions completed

3.2 innodb_fast_shutdown=1，innodb_force_recovery=3

    配置说明：异常停止DB服务时，不需要完成full purge和insert buffer操作，但是缓冲池的脏数据需要刷新到磁盘；服务启动的时候，忽略检查corrupt页，也阻止主线程的运行，并且不执行事务回滚操作。

    当innodb_force_recovery 值为1-3时，允许SELECT TABLE ，DROP or CREATE tables；innodb_force_recovery 值为>=4时，5.7.17之前版本支持DROP TABLE，5.7.18后版本不支持。

    这个配置适用于这种情况：有某些大表执行alter或者大量数据修改操作生成大量undo宕机，那么这个情况下，可以进入cnf配置文件修改innodb_force_recovery=3，然后把再做undo操作的表格数据导出来或者利用备份文件的数据，再drop掉这个表格，进入cnf配置文件，修改参数为0，重启DB服务，会发现，rollback过程非常快执行结束，因为找不到对应表格，所以rollback非常快。

 

    Tips: 如何查找在undo操作的表格？

    数据库crash后，第一个正常启动恢复连接，连进数据库里边，操作所有表格，不支持insert update 的表格都属于正在undo的表。

 

3.2.1 操作过程

#1 tailf error.log查看mysql错误日志,动态滚动查看
mysql> show global variables like 'log_error';
tailf /data/mysql/mysql3310/data/error.log

#2 测试库中开启事务，insert 10w行记录，不提交事务
mysql> begin;insert into orders select * from orders.orders limit 100000;
Query OK, 0 rows affected (0.00 sec)

Query OK, 100000 rows affected (37.55 sec)
Records: 100000  Duplicates: 0  Warnings: 0

#3 查找mysql进程号，杀进程
[root@localhost opt]# ps axu | grep mysql
[root@localhost opt]# kill -9 mysql的进程号

#4 在cnf文件中指定innodb_force_recovery=3,启动服务，检查是否修改成功
[root@localhost ~]# vim /data/mysql/mysql3310.cnf
#添加innodb_force_recovery参数设置
[mysqld]
innodb_force_recovery=3

#5 启动mysql服务
[root@localhost ~]# mysqld --defaults-file=/data/mysql/mysql3310.cnf &

#6 到tailf error.log窗口查看错误
#发现没有进行undo操作，同时全库仅支持select drop create，不支持其他所有操作

3.2.2 error log解析

启动mysqld进程

2017-03-17T15:12:14.317391Z 0 [Note] mysqld (mysqld 5.7.14-log) starting as process 32094 ...

 

读取ibdata的LSN

读取redo文件的checkpoint，从该点的LSN开始查找MLOG_CHECKPOINT

发现MLOG_CHECKPOINT日志，提示：Database was not shutdown normally !  

2017-03-17T15:12:16.478403Z 0 [Note] InnoDB: Log scan progressed past the checkpoint lsn 898935661420

2017-03-17T15:12:16.478579Z 0 [Note] InnoDB: Doing recovery: scanned up to log sequence number 898935661429

2017-03-17T15:12:16.532923Z 0 [Note] InnoDB: Doing recovery: scanned up to log sequence number 898935661429

2017-03-17T15:12:16.533063Z 0 [Note] InnoDB: Database was not shutdown normally!

2017-03-17T15:12:16.533105Z 0 [Note] InnoDB: Starting crash recovery.

 

检测需要重做跟回滚的事务

由于没有需要redo的事务，但是有undo事务，开始undo操作

加载redo log中的96个系统回滚段 rollbak segment，32个不需要redo 的临时表空间的回滚段

2017-03-17T15:12:17.052734Z 0 [Note] InnoDB: 1 transaction(s) which must be rolled back or cleaned up in total 100000 row operations to undo

 

获取binlog回滚xid列表，但是这里注意，没有做 回滚操作

2017-03-17T15:12:17.053009Z 0 [Note] InnoDB: Trx id counter is 5718016

2017-03-17T15:12:17.321987Z 0 [Note] InnoDB: Last MySQL binlog file position 0 37774, file name bin_log.000016

 

启动innodb，加载buffer pool ，警告当前 innodb_force_recovery 设置为3

2017-03-17T15:12:17.518732Z 0 [Note] InnoDB: 5.7.14 started; log sequence number 898935661429

2017-03-17T15:12:17.518789Z 0 [Note] InnoDB: !!! innodb_force_recovery is set to 3 !!!

2017-03-17T15:12:17.519305Z 0 [Note] InnoDB: Loading buffer pool(s) from /data/mysql/mysql3310/data/ib_buffer_pool

 

mysqld正常运行提供用户使用，但是，全库仅提供readonly

2017-03-17T15:12:18.521680Z 0 [Note] mysqld: ready for connections.

Version: '5.7.14-log'  socket: '/tmp/mysql3310.sock'  port: 3310  MySQL Community Server (GPL)

2017-03-17T15:13:03.125686Z 2 [ERROR] InnoDB: innodb_force_recovery is on. We do not allow database modifications by the user. Shut down mysqld and edit my.cnf to set innodb_force_recovery=0

 

    整个过程15:12:14启动，15:12:18 DB提供部分服务，耗时4s。但是由于没有做undo操作，错误日志提醒 We do not allow database modifications by the user. 不支持当前用户进行数据库修改操作，仅支持select table，drop table，create table操作，其他所有操作都不支持。

    这种情况下启动数据库后，可以支持你dump出正在做undo的表格数据，然后drop掉它，如果你有备份文件恢复，那么则不需要dump，直接drop，然后修改cnf配置文件，设置innodb_force_recovery=0 ，重启数据库服务，这个时候，innodb 的undo recovery非常快，因为找不到对应的表格操作，所以都是直接挑过处理。正常恢复后，赶紧把drop掉的表格从备份文件或者dump出来的sql文件中恢复回来。注意注意！！！！这种情况要权衡利弊，从时间耗时跟操作安全数据安全考虑，是undo recovery快还是你如此操作快，然后一定一定要跟你的上级或者领导报备操作的风险性，不要默默干，要报告！！！

2017-03-17T15:12:14.317391Z 0 [Note] mysqld (mysqld 5.7.14-log) starting as process 32094 ...
2017-03-17T15:12:14.430101Z 0 [Note] InnoDB: PUNCH HOLE support not available
2017-03-17T15:12:14.430586Z 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2017-03-17T15:12:14.430732Z 0 [Note] InnoDB: Uses event mutexes
2017-03-17T15:12:14.430874Z 0 [Note] InnoDB: GCC builtin __sync_synchronize() is used for memory barrier
2017-03-17T15:12:14.430993Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.3
2017-03-17T15:12:14.431084Z 0 [Note] InnoDB: Using Linux native AIO
2017-03-17T15:12:14.433127Z 0 [Note] InnoDB: Number of pools: 1
2017-03-17T15:12:14.434016Z 0 [Note] InnoDB: Not using CPU crc32 instructions
2017-03-17T15:12:14.443970Z 0 [Note] InnoDB: Initializing buffer pool, total size = 9G, instances = 8, chunk size = 128M
2017-03-17T15:12:16.158820Z 0 [Note] InnoDB: Completed initialization of buffer pool
2017-03-17T15:12:16.380118Z 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().
2017-03-17T15:12:16.409819Z 0 [Note] InnoDB: Highest supported file format is Barracuda.
2017-03-17T15:12:16.478403Z 0 [Note] InnoDB: Log scan progressed past the checkpoint lsn 898935661420
2017-03-17T15:12:16.478579Z 0 [Note] InnoDB: Doing recovery: scanned up to log sequence number 898935661429
2017-03-17T15:12:16.532923Z 0 [Note] InnoDB: Doing recovery: scanned up to log sequence number 898935661429
2017-03-17T15:12:16.533063Z 0 [Note] InnoDB: Database was not shutdown normally!
2017-03-17T15:12:16.533105Z 0 [Note] InnoDB: Starting crash recovery.
2017-03-17T15:12:17.052734Z 0 [Note] InnoDB: 1 transaction(s) which must be rolled back or cleaned up in total 100000 row operations to undo
2017-03-17T15:12:17.053009Z 0 [Note] InnoDB: Trx id counter is 5718016
2017-03-17T15:12:17.321987Z 0 [Note] InnoDB: Last MySQL binlog file position 0 37774, file name bin_log.000016
2017-03-17T15:12:17.460435Z 0 [Note] InnoDB: Removed temporary tablespace data file: "ibtmp1"
2017-03-17T15:12:17.460673Z 0 [Note] InnoDB: Creating shared tablespace for temporary tables
2017-03-17T15:12:17.461075Z 0 [Note] InnoDB: Setting file './ibtmp1' size to 12 MB. Physically writing the file full; Please wait ...
2017-03-17T15:12:17.512923Z 0 [Note] InnoDB: File './ibtmp1' size is now 12 MB.
2017-03-17T15:12:17.516337Z 0 [Note] InnoDB: 96 redo rollback segment(s) found. 96 redo rollback segment(s) are active.
2017-03-17T15:12:17.516617Z 0 [Note] InnoDB: 32 non-redo rollback segment(s) are active.
2017-03-17T15:12:17.518732Z 0 [Note] InnoDB: 5.7.14 started; log sequence number 898935661429
2017-03-17T15:12:17.518789Z 0 [Note] InnoDB: !!! innodb_force_recovery is set to 3 !!!
2017-03-17T15:12:17.519305Z 0 [Note] InnoDB: Loading buffer pool(s) from /data/mysql/mysql3310/data/ib_buffer_pool
2017-03-17T15:12:17.521217Z 0 [Note] Plugin 'FEDERATED' is disabled.
2017-03-17T15:12:17.694697Z 0 [Note] Recovering after a crash using /data/mysql/mysql3310/logs/bin_log
2017-03-17T15:12:17.694882Z 0 [Note] Starting crash recovery...
2017-03-17T15:12:17.695070Z 0 [Note] Crash recovery finished.
2017-03-17T15:12:18.197454Z 0 [Warning] Failed to set up SSL because of the following SSL library error: SSL context is not usable without certificate and private key
2017-03-17T15:12:18.197584Z 0 [Note] Server hostname (bind-address): '*'; port: 3310
2017-03-17T15:12:18.197804Z 0 [Note] IPv6 is available.
2017-03-17T15:12:18.197910Z 0 [Note]   - '::' resolves to '::';
2017-03-17T15:12:18.197981Z 0 [Note] Server socket created on IP: '::'.
2017-03-17T15:12:18.391615Z 0 [Note] InnoDB: Buffer pool(s) load completed at 170317 23:12:18
2017-03-17T15:12:18.414950Z 0 [Warning] 'user' entry 'mysql.sys@localhost' ignored in --skip-name-resolve mode.
2017-03-17T15:12:18.415223Z 0 [Warning] 'db' entry 'sys mysql.sys@localhost' ignored in --skip-name-resolve mode.
2017-03-17T15:12:18.415340Z 0 [Warning] 'proxies_priv' entry '@ root@localhost' ignored in --skip-name-resolve mode.
2017-03-17T15:12:18.446935Z 0 [Warning] 'tables_priv' entry 'sys_config mysql.sys@localhost' ignored in --skip-name-resolve mode.
2017-03-17T15:12:18.520569Z 0 [Note] Event Scheduler: Loaded 0 events
2017-03-17T15:12:18.521680Z 0 [Note] mysqld: ready for connections.
Version: '5.7.14-log'  socket: '/tmp/mysql3310.sock'  port: 3310  MySQL Community Server (GPL)
2017-03-17T15:13:03.125686Z 2 [ERROR] InnoDB: innodb_force_recovery is on. We do not allow database modifications by the user. Shut down mysqld and edit my.cnf to set innodb_force_recovery=0

 

参考文章：

https://dev.mysql.com/doc/refman/5.7/en/innodb-parameters.html

http://www.sysdb.cn/index.php/2016/01/14/innodb-recovery/?utm_source=tuicool&utm_medium=referral

http://mysql.taobao.org/monthly/2015/06/01/