电脑在使用过程中死机，重启后发现mysql没有启动成功，查看错误日志发现是innodb出现问题导致mysql启动失败。
错误日志
$ mysql.server start Starting MySQL . ERROR! The server quit without updating PID file (/usr/local/var/mysql/fdipzonedeMacBook-Air.local.pid).22:08:37 mysqld_safe Starting mysqld daemon with databases from /usr/local/var/mysql2016-04-23 22:08:38 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).2016-04-23 22:08:38 0 [Note] /usr/local/Cellar/mysql/5.6.24/bin/mysqld (mysqld 5.6.24) starting as process 3604 ...2016-04-23 22:08:38 3604 [Warning] Setting lower_case_table_names=2 because file system for /usr/local/var/mysql/ is case insensitive2016-04-23 22:08:38 3604 [Note] Plugin 'FEDERATED' is disabled.2016-04-23 22:08:38 3604 [Note] InnoDB: Using atomics to ref count buffer pool pages2016-04-23 22:08:38 3604 [Note] InnoDB: The InnoDB memory heap is disabled2016-04-23 22:08:38 3604 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins2016-04-23 22:08:38 3604 [Note] InnoDB: Memory barrier is not used2016-04-23 22:08:38 3604 [Note] InnoDB: Compressed tables use zlib 1.2.32016-04-23 22:08:38 3604 [Note] InnoDB: Using CPU crc32 instructions2016-04-23 22:08:38 3604 [Note] InnoDB: Initializing buffer pool, size = 128.0M2016-04-23 22:08:38 3604 [Note] InnoDB: Completed initialization of buffer pool2016-04-23 22:08:38 3604 [Note] InnoDB: Highest supported file format is Barracuda.2016-04-23 22:08:38 3604 [Note] InnoDB: Log scan progressed past the checkpoint lsn 689299334402016-04-23 22:08:38 3604 [Note] InnoDB: Database was not shutdown normally!2016-04-23 22:08:38 3604 [Note] InnoDB: Starting crash recovery.2016-04-23 22:08:38 3604 [Note] InnoDB: Reading tablespace information from the .ibd files...2016-04-23 22:08:38 3604 [ERROR] InnoDB: checksum mismatch in tablespace ./test_user/user_recommend_code#P#pmax.ibd (table test_user/user_recommend_code#P#pmax)2016-04-23 22:08:38 3604 [Note] InnoDB: Page size:1024 Pages to analyze:642016-04-23 22:08:38 3604 [Note] InnoDB: Page size: 1024, Possible space_id count:02016-04-23 22:08:38 3604 [Note] InnoDB: Page size:2048 Pages to analyze:482016-04-23 22:08:38 3604 [Note] InnoDB: Page size: 2048, Possible space_id count:02016-04-23 22:08:38 3604 [Note] InnoDB: Page size:4096 Pages to analyze:242016-04-23 22:08:38 3604 [Note] InnoDB: Page size: 4096, Possible space_id count:02016-04-23 22:08:38 3604 [Note] InnoDB: Page size:8192 Pages to analyze:122016-04-23 22:08:38 3604 [Note] InnoDB: Page size: 8192, Possible space_id count:02016-04-23 22:08:38 3604 [Note] InnoDB: Page size:16384 Pages to analyze:62016-04-23 22:08:38 3604 [Note] InnoDB: VALID: space:2947354 page_no:3 page_size:163842016-04-23 22:08:38 3604 [Note] InnoDB: Page size: 16384, Possible space_id count:12016-04-23 22:08:38 3604 [Note] InnoDB: space_id:2947354, Number of pages matched: 1/1 (16384)2016-04-23 22:08:38 3604 [Note] InnoDB: Chosen space:29473542016-04-23 22:08:38 3604 [Note] InnoDB: Restoring page 0 of tablespace 29473542016-04-23 22:08:38 3604 [Warning] InnoDB: Doublewrite does not have page_no=0 of space: 29473542016-04-23 22:08:38 7fff79b9e300 InnoDB: Operating system error number 2 in a file operation. InnoDB: The error means the system cannot find the path specified. InnoDB: If you are installing InnoDB, remember that you must create InnoDB: directories yourself, InnoDB does not create them. InnoDB: Error: could not open single-table tablespace file ./test_user/user_recommend_code#P#pmax.ibdInnoDB: We do not continue the crash recovery, because the table may become InnoDB: corrupt if we cannot apply the log records in the InnoDB log to it. InnoDB: To fix the problem and start mysqld: InnoDB: 1) If there is a permission problem in the file and mysqld cannot InnoDB: open the file, you should modify the permissions. InnoDB: 2) If the table is not needed, or you can restore it from a backup, InnoDB: then you can remove the .ibd file, and InnoDB will do a normal InnoDB: crash recovery and ignore that table. InnoDB: 3) If the file system or the disk is broken, and you cannot remove InnoDB: the .ibd file, you can set innodb_force_recovery > 0 in my.cnf InnoDB: and force InnoDB to continue crash recovery here.
解决方法
1.如果数据不重要或已经有备份，只需要恢复mysql启动
进入mysql目录，一般是：/usr/local/var/mysql/
删除ib_logfile*
删除ibdata*
删除所有数据库物理目录（例如数据库为test_db,则执行rm -rf test_db）
重启动mysql
重新建立数据库或使用备份覆盖
2.如果数据很重要且没有备份
可以使用innodb_force_recovery参数，使mysqld跳过恢复步骤，启动mysqld，将数据导出然后重建数据库。
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
(SRV_FORCE_IGNORE_CORRUPT):忽略检查到的corrupt页。
(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。
(SRV_FORCE_NO_TRX_UNDO):不执行事务回滚操作。
(SRV_FORCE_NO_IBUF_MERGE):不执行插入缓冲的合并操作。
(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。
(SRV_FORCE_NO_LOG_REDO):不执行前滚的操作。
在my.cnf(windows是my.ini)中加入
innodb_force_recovery = 6
innodb_purge_thread = 0
重启mysql
这时只可以执行select,create,drop操作，但不能执行insert,update,delete操作
执行逻辑导出，完成后将innodb_force_recovery=0，innodb_purge_threads=1，然后重建数据库，最后把导出的数据重新导入
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