【场景】MySQL版本：Percona-Server 5.6.23，相关主要参数：

server_id = 3306
sync_binlog=1
gtid_mod = on
enforce-gtid-consistency = 1
log-slave-updates = 1
relay-log-purge = 1
relay_log_recovery = 1
master_info_repository = "TABLE"
relay_log_info_repository = "TABLE"

打算部署一个新的slave实例用于测试，图方便从master上直接把mysql这个系统库整个目录拷贝到slave上，进行初始化后，执行 CHANGE MASTER 配置主从复制，但却提示错误信息：

mysql> change master to master_host=’10.x.x.x’,master_port=3306,master_user=’repl’,master_password=’xx’,master_auto_position=1;
ERROR 1794 (HY000): Slave is not configured or failed to initialize properly. You must at least set –server-id to enable either a master or a slave. Additional error messages can be found in the MySQL error log.

看到这个错误信息，最直觉的反应是 server_id 设置错误了，比如和 master 的ID重复了。经过检查，确认不是这个原因，尝试检查了其他参数，也提示同样的错误。另外奇怪的是，上面的错误信息，未被记录到错误日志中。

【分析】应该注意到一点，上面提到初始化slave实例时，是从master上直接拷贝mysql系统库整个目录的，但并没有同时也拷贝 ibdata1、ib_logfile* 等InnoDB相关文件。其实问题就在这里，因为mysql系统库中，下面这几个表是采用InnoDB引擎的，所以初始化后，无法正常读写：

innodb_index_stats
innodb_table_stats
slave_master_info
slave_relay_log_info
slave_worker_info

经验证，通过客户端访问mysql库时，就会提示下面的错误信息了：

2015-05-04 17:21:25 14407 [Warning] InnoDB: Cannot open table mysql/innodb_index_stats from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem.
2015-05-04 17:21:25 14407 [Warning] InnoDB: Cannot open table mysql/innodb_table_stats from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem.
2015-05-04 17:21:25 14407 [Warning] InnoDB: Cannot open table mysql/slave_master_info from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem.
2015-05-04 17:21:25 14407 [Warning] InnoDB: Cannot open table mysql/slave_relay_log_info from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem.
2015-05-04 17:21:25 14407 [Warning] InnoDB: Cannot open table mysql/slave_worker_info from the internal data dictionary of InnoDB though the .frm file for the table exists. See http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem.

【解决】本次案例中造成上述问题的原因是没有按照标准流程进行初始化，或者没有把master上的全部相关文件都拷贝到slave上去，导致mysql库下的几个InnoDB表无法使用。

解决的方法有两个：

1、删解除mysql系统库目录下上述几个表对应的ibd文件，执行 mysql_install_db 重新初始化；

2、从master将整个数据库全部文件都拷贝到slave上，并确认InnoDB的共享表空间文件及REDO LOG大小配置和master上是一致的；