mysql ibdata1损坏

机房一台服务器上的mysql运行一段时间了，突然出现了一个很奇怪的现象：重启后无法恢复了！准确情况是：启动mysql后随即就又关闭了。

查看mysql错误日志如下：

160920 22:41:41 mysqld_safe Starting mysqld daemon with databases from /home/MysqlData/
2016-09-20 22:41:41 0 [Note] /Data/app/mysql5.6.25/bin/mysqld (mysqld 5.6.25-log) starting as process 32372 ...
2016-09-20 22:41:42 32372 [Note] Plugin 'FEDERATED' is disabled.
2016-09-20 22:41:42 32372 [Warning] option 'innodb-write-io-threads': unsigned value 1000 adjusted to 64
2016-09-20 22:41:42 32372 [Warning] option 'innodb-read-io-threads': unsigned value 1000 adjusted to 64
2016-09-20 22:41:42 32372 [Note] InnoDB: Using atomics to ref count buffer pool pages
2016-09-20 22:41:42 32372 [Note] InnoDB: The InnoDB memory heap is disabled
2016-09-20 22:41:42 32372 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2016-09-20 22:41:42 32372 [Note] InnoDB: Memory barrier is not used
2016-09-20 22:41:42 32372 [Note] InnoDB: Compressed tables use zlib 1.2.3
2016-09-20 22:41:42 32372 [Note] InnoDB: Using CPU crc32 instructions
2016-09-20 22:41:42 32372 [Note] InnoDB: Initializing buffer pool, size = 1.0G
2016-09-20 22:41:42 32372 [Note] InnoDB: Completed initialization of buffer pool
2016-09-20 22:41:42 32372 [Note] InnoDB: Highest supported file format is Barracuda.
2016-09-20 22:41:42 32372 [Note] InnoDB: Log scan progressed past the checkpoint lsn 20293587957
2016-09-20 22:41:42 32372 [Note] InnoDB: Database was not shutdown normally!
2016-09-20 22:41:42 32372 [Note] InnoDB: Starting crash recovery.
2016-09-20 22:41:42 32372 [Note] InnoDB: Reading tablespace information from the .ibd files...
2016-09-20 22:41:42 32372 [Note] InnoDB: Restoring possible half-written data pages 
2016-09-20 22:41:42 32372 [Note] InnoDB: from the doublewrite buffer...
InnoDB: Doing recovery: scanned up to log sequence number 20293596130
2016-09-20 22:41:42 32372 [Note] InnoDB: Starting an apply batch of log records to the database...
InnoDB: Progress in percent: 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 
InnoDB: Apply batch completed
InnoDB: Last MySQL binlog file position 0 136254, file name mysql-bin.000013
2016-09-20 22:41:43 32372 [Note] InnoDB: 128 rollback segment(s) are active.
2016-09-20 22:41:43 32372 [Note] InnoDB: Waiting for purge to start
2016-09-20 22:41:43 7f77a9edd700 InnoDB: Assertion failure in thread 140151928772352 in file trx0purge.cc line 699
InnoDB: Failing assertion: purge_sys->iter.trx_no <= purge_sys->rseg->last_trx_no
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.
02:41:43 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.

分析日志后发现，数据库无法重启的原因是因为ibdata1文件损坏，重启后无法正常恢复。

解决办法：
需要跳过恢复步骤，修改my.cnf文件，在my.cnf中的[mysqld]中添加：
innodb_force_recovery = 6
innodb_purge_threads = 1

解释：
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。
具体数字对应的含义：
1-----(SRVFORCEIGNORECORRUPT):忽略检查到的corrupt页。
2-----(SRVFORCENOBACKGROUND):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-----(SRVFORCENOTRXUNDO):不执行事务回滚操作。
4-----(SRVFORCENOIBUFMERGE):不执行插入缓冲的合并操作。
5-----(SRVFORCENOUNDOLOGSCAN):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-----(SRVFORCENOLOG_REDO):不执行前滚的操作。

再次启动mysql就ok了~
如果还无法启动，则需要删除数据目录datafile下的 ibdata1,ib_logfile*等文件。
启动后导出MySQL数据库，重新恢复即可。