一、问题描述

今天在线运行的一个mysql崩溃了。
查看错误日志，如下：

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161108 11:36:45 mysqld_safe Starting mysqld daemon with databases from /usr/local/mysql/var

2017-08-15 11:36:46 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).

2017-08-15 11:36:46 5497 [Note] Plugin 'FEDERATED' is disabled.

2017-08-15 11:36:46 7f11c48e1720 InnoDB: Warning: Using innodb_additional_mem_pool_size is DEPRECATED. This option may be removed in future releases, together with the option innodb_use_sys_malloc and with the InnoDB's internal memory allocator.

2017-08-15 11:36:46 5497 [Note] InnoDB: Using atomics to ref count buffer pool pages

2017-08-15 11:36:46 5497 [Note] InnoDB: The InnoDB memory heap is disabled

2017-08-15 11:36:46 5497 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins

2017-08-15 11:36:46 5497 [Note] InnoDB: Memory barrier is not used

2017-08-15 11:36:46 5497 [Note] InnoDB: Compressed tables use zlib 1.2.3

2017-08-15 11:36:46 5497 [Note] InnoDB: Using CPU crc32 instructions

2017-08-15 11:36:46 5497 [Note] InnoDB: Initializing buffer pool, size = 16.0M

2017-08-15 11:36:46 5497 [Note] InnoDB: Completed initialization of buffer pool

InnoDB: Database page corruption on disk or a failed

InnoDB: file read of page 5.

InnoDB: You may have to recover from a backup.

2017-08-15 11:36:46 7f11c48e1720 InnoDB: Page dump in ascii and hex (16384 bytes):

 len 16384; hex 7478d078000000050000000000000000000000000f271f4d000700000000000000000000000000000000001b4000000000000000000200f20000000000000006000000000000002d000000000000002e000000000000002f0000000000000030000000000（省略很多类似代码）

InnoDB: End of page dump

2017-08-15 11:36:46 7f11c48e1720 InnoDB: uncompressed page, stored checksum in field1 1954074744, calculated checksums for field1: crc32 993334256, innodb 2046145943, none 3735928559, stored checksum in field2 1139795846, calculated checksums for field2: crc32 993334256, innodb 1606613742, none 3735928559, page LSN 0 254222157, low 4 bytes of LSN at page end 254221236, page number (if stored to page already) 5, space id (if created with >= MySQL-4.1.1 and stored already) 0

InnoDB: Page may be a transaction system page

InnoDB: Database page corruption on disk or a failed

InnoDB: file read of page 5.

InnoDB: You may have to recover from a backup.

InnoDB: It is also possible that your operating

InnoDB: system has corrupted its own file cache

InnoDB: and rebooting your computer removes the

InnoDB: error.

InnoDB: If the corrupt page is an index page

InnoDB: you can also try to fix the corruption

InnoDB: by dumping, dropping, and reimporting

InnoDB: the corrupt table. You can use CHECK

InnoDB: TABLE to scan your table for corruption.

InnoDB: See also http://dev.mysql.com/doc/refman/5.6/en/forcing-innodb-recovery.html

InnoDB: about forcing recovery.

InnoDB: Ending processing because of a corrupt database page.

2017-08-15 11:36:46 7f11c48e1720  InnoDB: Assertion failure in thread 139714288817952 in file buf0buf.cc line 4201

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/5.6/en/forcing-innodb-recovery.html

InnoDB: about forcing recovery.

03:36:46 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.

We will try our best to scrape up some info that will hopefully help

diagnose the problem, but since we have already crashed, 

something is definitely wrong and this may fail.

key_buffer_size=16777216

read_buffer_size=262144

max_used_connections=0

max_threads=1000

thread_count=0

connection_count=0

It is possible that mysqld could use up to 

key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 798063 K  bytes of memory

Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x0

Attempting backtrace. You can use the following information to find out

where mysqld died. If you see no messages after this, something went

terribly wrong...

stack_bottom = 0 thread_stack 0x40000

/usr/local/mysql/bin/mysqld(my_print_stacktrace+0x35)[0x8e64b5]

/usr/local/mysql/bin/mysqld(handle_fatal_signal+0x41b)[0x652fbb]

/lib64/libpthread.so.0(+0xf7e0)[0x7f11c44c77e0]

/lib64/libc.so.6(gsignal+0x35)[0x7f11c315d625]

/lib64/libc.so.6(abort+0x175)[0x7f11c315ee05]

/usr/local/mysql/bin/mysqld[0xa585c5]

/usr/local/mysql/bin/mysqld[0xa6c7b4]

/usr/local/mysql/bin/mysqld[0xa6cbc7]

/usr/local/mysql/bin/mysqld[0xa5bce2]

/usr/local/mysql/bin/mysqld[0xa1e2ba]

/usr/local/mysql/bin/mysqld[0xa0bf60]

/usr/local/mysql/bin/mysqld[0x95a427]

/usr/local/mysql/bin/mysqld(_Z24ha_initialize_handlertonP13st_plugin_int+0x48)[0x58f788]

/usr/local/mysql/bin/mysqld[0x6e4a36]

/usr/local/mysql/bin/mysqld(_Z11plugin_initPiPPci+0xb3e)[0x6e826e]

/usr/local/mysql/bin/mysqld[0x582d85]

/usr/local/mysql/bin/mysqld(_Z11mysqld_mainiPPc+0x4d8)[0x587d18]

/lib64/libc.so.6(__libc_start_main+0xfd)[0x7f11c3149d5d]

/usr/local/mysql/bin/mysqld[0x57a019]

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.

161108 11:36:46 mysqld_safe mysqld from pid file /usr/local/mysql/var/VM_241_49_centos.pid ended

------------------------------------------------------------------------------

二、问题分析

从日志中可以看出是innodb引擎出了问题。日志里提示到 http://dev.mysql.com/doc/refman/5.6/en/forcing-innodb-recovery.html查看强制恢复的方法。在mysql的配置文件my.cnf里找到 [mysqld]字段下，添加 innodb_force_recovery=1：

[mysqld]
innodb_force_recovery = 1

如果innodb_force_recovery = 1不生效，则可尝试2——6几个数字
然后重启mysql，重启成功。然后使用mysqldump或 pma 导出数据，执行修复操作等。修复完成后，把该参数注释掉，还原默认值0。
配置文件的参数：innodb_force_recovery
innodb_force_recovery影响整个InnoDB存储引擎的恢复状况。默认为0，表示当需要恢复时执行所有的恢复操作（即校验数据页/purge undo/insert buffer merge/rolling back&forward），当不能进行有效的恢复操作时，mysql有可能无法启动，并记录错误日志；
innodb_force_recovery可以设置为1-6,大的数字包含前面所有数字的影响。当设置参数值大于0后，可以对表进行select,create,drop操作,但insert,update或者delete这类操作是不允许的。

• 1(SRV_FORCE_IGNORE_CORRUPT):忽略检查到的corrupt页。
• 2(SRV_FORCE_NO_BACKGROUND):阻止主线程的运行，如主线程需要执行full purge操作，会导致crash。
• 3(SRV_FORCE_NO_TRX_UNDO):不执行事务回滚操作。
• 4(SRV_FORCE_NO_IBUF_MERGE):不执行插入缓冲的合并操作。
• 5(SRV_FORCE_NO_UNDO_LOG_SCAN):不查看重做日志，InnoDB存储引擎会将未提交的事务视为已提交。
• 6(SRV_FORCE_NO_LOG_REDO):不执行前滚的操作。

三、解析方案

一般修复方法参考：

第一种方法

建立一张新表：
create table demo_bak  #和原表结构一样，只是把INNODB改成了MYISAM。
把数据导进去
insert into demo_bak select * from demo;
删除掉原表：
drop table demo;
注释掉 innodb_force_recovery 之后，重启。
重命名：
rename table demo_bak to demo;
最后改回存储引擎：
alter table demo engine = innodb

第二种方法

另一个方法是使用mysqldump将表格导出，然后再导回到InnoDB表中。这两种方法的结果是相同的。 
备份导出(包括结构和数据)：
mysqldump -uroot -p123 test > test.sql
还原方法1：
use test;
source test.sql
还原方法2（系统命令行）：
mysql -uroot -p123 test < test.sql;
注意，CHECK TABLE命令在InnoDB数据库中基本上是没有用的。

第三种方法

1、配置my.cnf

配置innodb_force_recovery = 1或2——6几个数字，重启MySQL

2、导出数据脚本

mysqldump -uroot -p123 test > test.sql
导出SQL脚本。或者用Navicat将所有数据库/表导入到其他服务器的数据库中。
注意：这里的数据一定要备份成功。然后删除原数据库中的数据。

3、删除ib_logfile0、ib_logfile1、ibdata1

备份MySQL数据目录下的ib_logfile0、ib_logfile1、ibdata1三个文件，然后将这三个文件删除

4、配置my.cnf

将my.cnf中innodb_force_recovery = 1或2——6几个数字这行配置删除或者配置为innodb_force_recovery = 0，重启MySQL服务

5、将数据导入MySQL数据库

mysql -uroot -p123 test < test.sql; 或者用Navicat将备份的数据导入到数据库中。
此种方法下要注意的问题：
  1、ib_logfile0、ib_logfile1、ibdata1这三个文件一定要先备份后删除；
  2、一定要确认原数据导出成功了
  3、当数据导出成功后，删除原数据库中的数据时，如果提示不能删除，可在命令行进入MySQL的数据目录，手动删除相关数据库的文件夹或者数据库文件夹下的数据表文件，前提是数据一定导出或备份成功。