1. 环境说明
RHEL 6.4 x86_64 + MySQL 5.5.37和MySQL 5.6.19
blog地址：http://blog.csdn.net/hw_libo/article/details/39215723
2. 案例：redo log文件（ib_logfile）大小参数被修改：innodb_log_file_size
innodb_log_file_size = 256M -- 修改为200M
版本是5.5的，启动失败，会出现如下错误：
InnoDB: Error: log file ./ib_logfile0 is of different size 0 268435456 bytes ## 原来redo log的大小 InnoDB: than specified in the .cnf file 0 209715200 bytes! ## redo log被修改的大小 140912 0:01:12 [ERROR] Plugin 'InnoDB' init function returned error. 140912 0:01:12 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed. 140912 0:01:12 [ERROR] Unknown/unsupported storage engine: InnoDB 140912 0:01:12 [ERROR] Aborting版本是5.6.16之后的，正常启动，会自动将原来的redo log删除，然后重新生成新的redo log（这个比较重要）：
2014-09-11 21:57:05 1093 [Warning] InnoDB: Resizing redo log from 2*16384 to 2*12800 pages, LSN=71249171 2014-09-11 21:57:05 1093 [Warning] InnoDB: Starting to delete and rewrite log files. ## 删除原redo log 2014-09-11 21:57:05 1093 [Note] InnoDB: Setting log file ./ib_logfile101 size to 200 MB InnoDB: Progress in MB: 100 200 2014-09-11 21:57:06 1093 [Note] InnoDB: Setting log file ./ib_logfile1 size to 200 MB InnoDB: Progress in MB: 100 200 2014-09-11 21:57:07 1093 [Note] InnoDB: Renaming log file ./ib_logfile101 to ./ib_logfile0 2014-09-11 21:57:07 1093 [Warning] InnoDB: New log files created, LSN=71249171 ## 新redo log重建完毕原redo log大小：2*16384*8(page的大小为8k)/1024=256MB
新redo log大小：2*12800*8/1024=200MB
3. 案例：ibdata1文件大小参数被修改：innodb_data_file_path
（1）ibdata1从大改小
innodb_data_file_path = ibdata1:1G:autoextend -- 修改为：ibdata1:300M:autoextend
在版本是5.5和5.6中，启动正常，并且日志中没有任何异常。但是如果将autoextend去掉，就会报错，启动失败，如：[版本：5.5.37]
InnoDB: Error: data file ./ibdata1 is of a different size InnoDB: 65536 pages (rounded down to MB) InnoDB: than specified in the .cnf file 19200 pages! 140911 23:51:53 InnoDB: Could not open or create data files. 140911 23:51:53 InnoDB: If you tried to add new data files, and it failed here, 140911 23:51:53 InnoDB: you should now edit innodb_data_file_path in my.cnf back 140911 23:51:53 InnoDB: to what it was, and remove the new ibdata files InnoDB created 140911 23:51:53 InnoDB: in this failed attempt. InnoDB only wrote those files full of 140911 23:51:53 InnoDB: zeros, but did not yet use them in any way. But be careful: do not 140911 23:51:53 InnoDB: remove old data files which contain your precious data! 140911 23:51:53 [ERROR] Plugin 'InnoDB' init function returned error. 140911 23:51:53 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed. 140911 23:51:53 [ERROR] Unknown/unsupported storage engine: InnoDB 140911 23:51:53 [ERROR] Aborting 原来的ibdata1大小为：65536*8*2/1024=1024M=1G 当前ibdata1被修改为：19200*8*2/1024=300M（2）ibdata1值小改大
比如：
innodb_data_file_path = ibdata1:1G:autoextend -- 修改为：ibdata1:1200M:autoextend
那么会在启动时出现如下错误：
*****在5.5版本中：[版本：5.5.37]
InnoDB: Error: auto-extending data file ./ibdata1 is of a different size InnoDB: 65536 pages (rounded down to MB) than specified in the .cnf file: InnoDB: initial 76800 pages, max 0 (relevant if non-zero) pages! 140911 23:57:43 InnoDB: Could not open or create data files. 140911 23:57:43 InnoDB: If you tried to add new data files, and it failed here, 140911 23:57:43 InnoDB: you should now edit innodb_data_file_path in my.cnf back 140911 23:57:43 InnoDB: to what it was, and remove the new ibdata files InnoDB created 14091