找回“消失”的InnoDB引擎

   夜里重做主从复制，顺便调整了下从库的my.cnf。早上想起从库忘了重启，打完命令接着开启slave，居然报错

Last_SQL_Errno: 1286
Last_SQL_Error: Error executing row event: 'Unknown storage engine 'InnoDB''

奇怪，怎么会报错不知道存储引擎InnoDB。查看下引擎：

mysql> show engines;
+--------------------+---------+-----------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                   | Transactions | XA   | Savepoints |
+--------------------+---------+-----------------------------------------------------------+--------------+------+------------+
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables | NO           | NO   | NO         |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                        | NO           | NO   | NO         |
| MyISAM             | DEFAULT | MyISAM storage engine                                     | NO           | NO   | NO         |
| CSV                | YES     | CSV storage engine                                        | NO           | NO   | NO         |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                     | NO           | NO   | NO         |
+--------------------+---------+-----------------------------------------------------------+--------------+------+------------+
5 rows in set (0.01 sec)

没了，InnoDB真的没了。我的心一下慌了，从来没听说过过引擎会自己消失的啊！再看看错误日志怎么说

130829  8:42:30 [Note] Slave I/O thread: connected to master 'slave@192.168.0.153:3306',replication started in log 'mysql-bin.000023' at position 232546566
130829  8:42:30 [ERROR] Slave SQL: Error executing row event: 'Unknown storage engine 'InnoDB'', Error_code: 1286
130829  8:42:30 [Warning] Slave: Unknown storage engine 'InnoDB' Error_code: 1286
130829  8:42:30 [ERROR] Error running query, slave SQL thread aborted. Fix the problem, and restart the slave SQL thread with "SLAVE START". We stopped at log 'mysql-bin.000023' position 225856952

看来InnoDB确实消失了。

遇到问题要先靠自己，这样才会提高自己。想想事件的过程：InnoDB消失了。为什么会消失？为什么是今天消失？我都有做过什么?好好想想。。。。

配置文件，没错，我夜里调整了my.cnf，然后早上重启mysql，然后InnoDB不见了。OK，原因找到了。赶紧将调整前后的配置文件对比，看看咱都改了哪些啊，发现了最可疑的一个配置项：

innodb_log_files_in_group = 3

改回调整前的值2，重启mysql，开启slave，复制正常了，查看引擎，InnoDB也回来了！万幸啊。InnoDB的消失其实是因为修改配置导致mysql生成新的ib_logfile日志与旧的ib_logfile日志混乱引起的。整理下修改此配置项的操作步骤

service mysqld stop
cd到数据目录下
mv ib_logfile* 到其他目录下
修改innodb_log_files_in_group
service mysqld start