跨数据库server。跨实例訪问是比較常见的一种訪问方式，在Oracle中能够通过DB LINK的方式来实现。

对于MySQL而言，有一个FEDERATED存储引擎与之相相应。相同也是通过创建一个链接方式的形式来訪问远程server上的数据。本文简要描写叙述了FEDERATED存储引擎。以及演示了基于FEDERATED存储引擎跨实例訪问的演示样例。

1、FEDERATED存储引擎的描写叙述
  FEDERATED存储引擎同意在不使用复制或集群技术的情况下实现远程訪问数据库
  创建基于FEDERATED存储引擎表的时候，server在数据库文件夹仅创建一个表定义文件，即以表名开头的.frm文件。
  FEDERATED存储引擎表无不论什么数据存储到本地，即没有.myd文件
  对于远程server上表的操作与本地表操作一样，不过数据位于远程server
  基本流程例如以下：    

2、安装与启用FEDERATED存储引擎
  源代码安装MySQL时使用DWITH_FEDERATED_STORAGE_ENGINE来配置
  rpm安装方式缺省情况下已安装，只须要启用该功能就可以

3、准备远程server环境

-- 此演示中远程server与本地server为同一server上的多版本号多实例
-- 假定远程服务为：5.6.12(实例3406)
-- 假定本地server：5.6.21(实例3306)   
-- 基于实例3306创建FEDERATED存储引擎表test.federated_engine以到达訪问实例3406数据库tempdb.tb_engine的目的

[root@rhel64a ~]# cat /etc/issue
Red Hat Enterprise Linux Server release 6.4 (Santiago) 

--启动3406的实例
[root@rhel64a ~]# /u01/app/mysql/bin/mysqld_multi start 3406
[root@rhel64a ~]# mysql -uroot -pxxx -P3406 --protocol=tcp

root@localhost[(none)]> show variables like ‘server_id‘;
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| server_id     | 3406  |
+---------------+-------+

--实例3406的版本
root@localhost[tempdb]> show variables like ‘version‘;
+---------------+------------+
| Variable_name | Value      |
+---------------+------------+
| version       | 5.6.12-log |
+---------------+------------+

--创建数据库
root@localhost[(none)]> create database tempdb;
Query OK, 1 row affected (0.00 sec)

-- Author : Leshami
-- Blog   ：http://blog.csdn.net/leshami

root@localhost[(none)]> use tempdb
Database changed

--创建用于訪问的表
root@localhost[tempdb]> create table tb_engine as 
    -> select engine,support,comment from information_schema.engines;
Query OK, 9 rows affected (0.10 sec)
Records: 9  Duplicates: 0  Warnings: 0

--提取表的SQL语句用于创建为FEDERATED存储引擎表
root@localhost[tempdb]> show create table tb_engine \G
*************************** 1. row ***************************
       Table: tb_engine
Create Table: CREATE TABLE `tb_engine` (
  `engine` varchar(64) NOT NULL DEFAULT ‘‘,
  `support` varchar(8) NOT NULL DEFAULT ‘‘,
  `comment` varchar(80) NOT NULL DEFAULT ‘‘
) ENGINE=InnoDB DEFAULT CHARSET=utf8

--创建用于远程訪问的账户
root@localhost[tempdb]> grant all privileges on tempdb.* to ‘remote_user‘@‘192.168.1.131‘ identified by ‘xxx‘;
Query OK, 0 rows affected (0.00 sec)

root@localhost[tempdb]> flush privileges;
Query OK, 0 rows affected (0.00 sec)

4、演示FEDERATED存储引擎跨实例訪问

[root@rhel64a ~]# mysql -uroot -pxxx

root@localhost[(none)]> show variables like ‘version‘;
+---------------+--------+
| Variable_name | Value  |
+---------------+--------+
| version       | 5.6.21 |
+---------------+--------+

#查看是否支持FEDERATED引擎
root@localhost[(none)]> select * from information_schema.engines where engine=‘federated‘;
+-----------+---------+--------------------------------+--------------+------+------------+
| ENGINE    | SUPPORT | COMMENT                        | TRANSACTIONS | XA   | SAVEPOINTS |
+-----------+---------+--------------------------------+--------------+------+------------+
| FEDERATED | NO      | Federated MySQL storage engine | NULL         | NULL | NULL       |
+-----------+---------+--------------------------------+--------------+------+------------+

root@localhost[(none)]> exit
[root@rhel64a ~]# service mysql stop
Shutting down MySQL..[  OK  ]
#配置启用FEDERATED引擎
[root@rhel64a ~]# vi /etc/my.cnf
[root@rhel64a ~]# tail -7 /etc/my.cnf
[mysqld]
socket = /tmp/mysql3306.sock
port = 3306
pid-file = /var/lib/mysql/my3306.pid
user = mysql
server-id=3306/
federated         #加入该选项
[root@rhel64a ~]# service mysql start
Starting MySQL.[  OK  ]
[root@rhel64a ~]# mysql -uroot -pxxx
root@localhost[(none)]> select * from information_schema.engines where engine=‘federated‘;
+-----------+---------+--------------------------------+--------------+------+------------+
| ENGINE    | SUPPORT | COMMENT                        | TRANSACTIONS | XA   | SAVEPOINTS |
+-----------+---------+--------------------------------+--------------+------+------------+
| FEDERATED | YES     | Federated MySQL storage engine | NO           | NO   | NO         |
+-----------+---------+--------------------------------+--------------+------+------------+

root@localhost[(none)]> use test

-- 创建基于FEDERATED引擎的表federated_engine
root@localhost[test]> CREATE TABLE `federated_engine` (
    ->   `engine` varchar(64) NOT NULL DEFAULT ‘‘,
    ->   `support` varchar(8) NOT NULL DEFAULT ‘‘,
    ->   `comment` varchar(80) NOT NULL DEFAULT ‘‘
    -> ) ENGINE=FEDERATED DEFAULT CHARSET=utf8
    -> CONNECTION=‘mysql://remote_user:xxx@192.168.1.131:3406/tempdb/tb_engine‘;
Query OK, 0 rows affected (0.00 sec)

-- 以下是创建后表格式文件
root@localhost[test]> system ls -hltr /var/lib/mysql/test
total 12K
-rw-rw---- 1 mysql mysql 8.5K Oct 24 08:22 federated_engine.frm

--查询表federated_engine
root@localhost[test]> select * from federated_engine limit 2;
+------------+---------+---------------------------------------+
| engine     | support | comment                               |
+------------+---------+---------------------------------------+
| MRG_MYISAM | YES     | Collection of identical MyISAM tables |
| CSV        | YES     | CSV storage engine                    |
+------------+---------+---------------------------------------+

--更新表federated_engine
root@localhost[test]> update federated_engine set support=‘NO‘ where engine=‘CSV‘;
Query OK, 1 row affected (0.03 sec)
Rows matched: 1  Changed: 1  Warnings: 0

--查看更新后的结果
root@localhost[test]> select * from federated_engine where engine=‘CSV‘;
+--------+---------+--------------------+
| engine | support | comment            |
+--------+---------+--------------------+
| CSV    | NO      | CSV storage engine |
+--------+---------+--------------------+

5、创建FEDERATED引擎表的链接方式
scheme://user_name[:password]@host_name[:port_num]/db_name/tbl_name

    scheme: A recognized connection protocol. Only mysql is supported as the scheme value at this point.
    user_name: The user name for the connection. This user must have been created on the remote server, and must have suitable privileges to perform the required actions (SELECT, INSERT,UPDATE, and so forth) on the remote table.
    password: (Optional) The corresponding password for user_name.
    host_name: The host name or IP address of the remote server.
    port_num: (Optional) The port number for the remote server. The default is 3306.
    db_name: The name of the database holding the remote table.
    tbl_name: The name of the remote table. The name of the local and the remote table do not have to match.

链接演示样例样本:
    CONNECTION=‘mysql://username:password@hostname:port/database/tablename‘
    CONNECTION=‘mysql://username@hostname/database/tablename‘
    CONNECTION=‘mysql://username:password@hostname/database/tablename‘

6、涉及到的相关參考
    MySQL多实例配置(一)
    MySQL多实例配置(二)
    Linux 下MySQL源代码安装完整版
    MySQL 用户与权限管理