通常一个网站在初期访问量都比较小，所以一般的小架构足以支撑。但是，当网站逐渐发展起来后，随之而来的是大量的访问，这时候最先出现的瓶颈就是数据库了。因为数据的写入读取操作（I/O）是集群中响应速度最慢的，所以在集群建设时就要规划好后端存储架构。

后端存储数据库架构普遍是主从复制，这样解决了数据备份问题。但是，由前端来的读写请求都要经过主库，量小没问题，当量大到超过主库的性能极限时，主库分分钟会宕机。

为了避免主库宕机这种灾难性事件的发生，读写分离的设计诞生了！把写的请求只交给主库，读的请求由主库和从库一起分摊，这样就大大减轻了主库的负担。

大部分公司会由开发部门在软件层面实现对数据库的读写分离，其次可以选择读写分离的中间件如：TDDL、amoeba、cobar、MySQL-proxy、Atlas、MyCat。

本次测试采用MySQL官方发布的MySQL-proxy。

官网下载地址（二进制包）：https://downloads.mysql.com/archives/get/file/mysql-proxy-0.8.5-linux-el6-x86-64bit.tar.gz

测试环境：

[root@SQL-M ~]# cat /etc/redhat-release

CentOS release 6.8 (Final)

[root@SQL-M ~]# uname -r

2.6.32-642.el6.x86_64

MySQL-proxy   IP：192.168.0.86

MySQL-master  IP：192.168.0.88

MySQL-slave   IP：192.168.0.90

前提：MySQL主库与从库已经实现主从复制。

实现主从复制请参考我的前一篇博文：http://yuyicong.blog.51cto.com/11274530/1919158

接下来的操作在proxy服务器上：

[root@SQL-proxy ~]# cd /usr/local/src/

[root@SQL-proxy src]# wget https://downloads.mysql.com/archives/get/file/mysql-proxy-0.8.5-linux-el6-x86-64bit.tar.gz

[root@SQL-proxy src]# ll -h

total 12M

-rw-r--r-- 1 root root 12M Aug 19  2014 mysql-proxy-0.8.5-linux-el6-x86-64bit.tar.gz

[root@SQL-proxy src]# tar zxf mysql-proxy-0.8.5-linux-el6-x86-64bit.tar.gz -C /usr/local/

[root@SQL-proxy src]# cd ..

[root@SQL-proxy local]# mv mysql-proxy-0.8.5-linux-el6-x86-64bit/ mysql-proxy-0.8.5

[root@SQL-proxy local]# ll -d mysql-proxy-0.8.5

drwxr-xr-x  8 7161 wheel 4096 Aug 19  2014 mysql-proxy-0.8.5    # 看到所属用户和组有问题

[root@SQL-proxy local]# chown -R root:root mysql-proxy-0.8.5/  # 改为root

[root@SQL-proxy local]# ln -s mysql-proxy-0.8.5/ mysql-proxy    # 必备软连接

[root@SQL-proxy local]# cd mysql-proxy

[root@SQL-proxy mysql-proxy]# mkdir etc              # 创建 lua 脚本存放目录

[root@SQL-proxy mysql-proxy]# mkdir logs            # 创建日志目录

把实现读写分离的 lua 脚本复制到 etc 目录下

[root@SQL-proxy mysql-proxy]# cp share/doc/mysql-proxy/rw-splitting.lua etc/

[root@SQL-proxy mysql-proxy]# cp share/doc/mysql-proxy/admin-sql.lua etc/

创建启动参数文件，启动服务时命令行就不用老长老长的。

[root@SQL-proxy ~]# vim /etc/mysql-proxy.cnf

[mysql-proxy]
admin-username=proxy     # 连接主从mysql共有的用户
admin-password=123       # 连接用户的密码
proxy-address=192.168.0.86:3306   # mysql-proxy监听本地工作ip和端口，不加端口默认是4040，为了方便管理这里用3306
proxy-backend-addresses=192.168.0.87:3306    # 指定后端主库
proxy-read-only-backend-addresses=192.168.0.90:3306  # 指定后端只读从库
proxy-lua-script=/usr/local/mysql-proxy/etc/rw-splitting.lua  # 指定实现读写分离的lua脚本
admin-lua-script=/usr/local/mysql-proxy/etc/admin-sql.lua     # 指定管理脚本
pid-file=/var/run/mysql-proxy.pid
log-file=/usr/local/mysql-proxy/logs/mysql-proxy.log  # 日志位置
log-level=info  # 定义log日志级别，由高到低分别有(error|warning|info|message|debug)
daemon=true     # 以守护进程方式运行
keepalive=true  # work进程崩溃时，尝试重启

启动服务

[root@SQL-proxy ~]# /usr/local/mysql-proxy/bin/mysql-proxy --defaults-file=/etc/mysql-proxy.cnf

2017-04-24 16:40:19: (critical) mysql-proxy-cli.c:326: loading config from '/etc/mysql-proxy.cnf' failed: permissions of /etc/mysql-proxy.cnf aren't secure (0660 or stricter required)

2017-04-24 16:40:19: (message) Initiating shutdown, requested from mysql-proxy-cli.c:328

2017-04-24 16:40:19: (message) shutting down normally, exit code is: 1

！！看到无法启动，文件权限要改，因为文件里面有账号密码。

[root@SQL-proxy ~]# chmod 660 /etc/mysql-proxy.cnf     # 改权限

[root@SQL-proxy ~]# ll /etc/mysql-proxy.cnf

-rw-rw---- 1 root root 432 Apr 24 16:31 /etc/mysql-proxy.cnf

[root@SQL-proxy ~]# /usr/local/mysql-proxy/bin/mysql-proxy --defaults-file=/etc/mysql-proxy.cnf                                              #  重新启动

[root@SQL-proxy ~]# netstat -lntup   # 查看服务

Active Internet connections (only servers)

Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name

tcp        0      0 192.168.0.86:3306           0.0.0.0:*                   LISTEN      3086/mysql-proxy

老是命令行敲一长串命令肯定不科学了，直接上服务管理脚本。

[root@SQL-proxy ~]# vim /etc/init.d/mysql-proxy
#!/bin/bash
#
# mysql-proxy This script starts and stops the mysql-proxy daemon
#
# chkconfig: - 78 30
# processname: mysql-proxy
# description: mysql-proxy is a proxy daemon for mysql# Source function library.
. /etc/rc.d/init.d/functionsprog="/usr/local/mysql-proxy/bin/mysql-proxy"# Source networking configuration.
if [ -f /etc/sysconfig/network ]; then. /etc/sysconfig/network
fi# Check that networking is up.
[ ${NETWORKING} = "no" ] && exit 0DEFAULT_FILE=/etc/mysql-proxy.cnf
PROXY_PID=/var/run/mysql-proxy.pidRETVAL=0start() {echo -n $"Starting MySQL-proxy...  : "daemon $prog --defaults-file=$DEFAULT_FILERETVAL=$?echoif [ $RETVAL -eq 0 ]; thentouch /var/lock/subsys/mysql-proxy.lockfi
}stop() {echo -n $"Stopping MySQL-proxy...  : "killproc -p $PROXY_PID -d 3 $progRETVAL=$?echoif [ $RETVAL -eq 0 ]; thenrm -f /var/lock/subsys/mysql-proxy.lockrm -f $PROXY_PIDfi
}
# See how we were called.
case "$1" instart)start;;stop)stop;;restart)stopstart;;condrestart|try-restart)if status -p $PROXY_PIDFILE $prog >&/dev/null; thenstopstartfi;;status)status -p $PROXY_PID $prog;;*)echo "Usage: $0 {start|stop|restart|reload|status|condrestart|try-restart}"RETVAL=1;;
esacexit $RETVAL

[root@SQL-proxy ~]# chmod +x /etc/init.d/mysql-proxy   #  给执行权限

[root@SQL-proxy ~]# chkconfig mysql-proxy on           # 可以加入开机启动

测试一下脚本：

[root@SQL-proxy ~]# /etc/init.d/mysql-proxy status
mysql-proxy (pid  3086) is running...
[root@SQL-proxy ~]#
[root@SQL-proxy ~]# /etc/init.d/mysql-proxy stop
Stopping MySQL-proxy...  :                                 [  OK  ]
[root@SQL-proxy ~]#
[root@SQL-proxy ~]# /etc/init.d/mysql-proxy status
mysql-proxy is stopped
[root@SQL-proxy ~]# netstat -lntup
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name
tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN      1079/sshd
tcp        0      0 :::22                       :::*                        LISTEN      1079/sshd
[root@SQL-proxy ~]# /etc/init.d/mysql-proxy start
Starting MySQL-proxy...  :                                 [  OK  ]
[root@SQL-proxy ~]# /etc/init.d/mysql-proxy restart
Stopping MySQL-proxy...  :                                 [  OK  ]
Starting MySQL-proxy...  :                                 [  OK  ]
[root@SQL-proxy ~]#
[root@SQL-proxy ~]# netstat -lntup
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name
tcp        0      0 192.168.0.86:3306           0.0.0.0:*                   LISTEN      3143/mysql-proxy

以上MySQL-proxy服务器搭建完成，但是用于连接后端数据库的用户：proxy还需要在数据库端创建

数据库Master端：创建proxy用户，给增删改查权限

[root@SQL-M ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.5.55-log MySQL Community Server (GPL)Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.Master>
Master> grant insert,delete,update,select on *.* to proxy@'192.168.0.86' identified by '123';
Query OK, 0 rows affected (0.00 sec)Master> select user,host from mysql.user;                                       +-------+--------------+
| user  | host         |
+-------+--------------+
| root  | 127.0.0.1    |
| rep   | 192.168.0.%  |
| proxy | 192.168.0.86 |
| root  | localhost    |
+-------+--------------+
4 rows in set (0.00 sec)Master> show grants for proxy@'192.168.0.86';
+------------------------------------------------------------------------------------------------------------------------------------------+
| Grants for proxy@192.168.0.86                                                                                                            |
+------------------------------------------------------------------------------------------------------------------------------------------+
| GRANT SELECT, INSERT, UPDATE, DELETE ON *.* TO 'proxy'@'192.168.0.86' IDENTIFIED BY PASSWORD '*23AE809DDACAF96AF0FD78ED04B6A265E05AA257' |
+------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

Slave端：此时已经与主库一致拥有了proxy用户，但是从库只能读（select），所以要对proxy回收权限。

Slave> show grants for proxy@'192.168.0.86';
+------------------------------------------------------------------------------------------------------------------------------------------+
| Grants for proxy@192.168.0.86                                                                                                            |
+------------------------------------------------------------------------------------------------------------------------------------------+
| GRANT SELECT, INSERT, UPDATE, DELETE ON *.* TO 'proxy'@'192.168.0.86' IDENTIFIED BY PASSWORD '*23AE809DDACAF96AF0FD78ED04B6A265E05AA257' |
+------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)Slave> revoke insert,update,delete on *.* from proxy@'192.168.0.86'; # 只留查询权限
Query OK, 0 rows affected (0.00 sec)Slave> show grants for proxy@'192.168.0.86';
+------------------------------------------------------------------------------------------------------------------+
| Grants for proxy@192.168.0.86                                                                                    |
+------------------------------------------------------------------------------------------------------------------+
| GRANT SELECT ON *.* TO 'proxy'@'192.168.0.86' IDENTIFIED BY PASSWORD '*23AE809DDACAF96AF0FD78ED04B6A265E05AA257' |
+------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

测试读写分离

为了方便测试，修改 rw-splitting.lua 脚本里触发读写分离参数

[root@SQL-proxy ~]# vim /usr/local/mysql-proxy/etc/rw-splitting.lua
-- connection pool
if not proxy.global.config.rwsplit thenproxy.global.config.rwsplit = {min_idle_connections = 1,  # 默认超过4个连接数时，才开始读写分离，改为1max_idle_connections = 8,  # 默认最大连接数8，不动它is_debug = false}
end[root@SQL-proxy ~]# /etc/init.d/mysql-proxy restart       # 重启一下
Stopping MySQL-proxy...  :                                 [  OK  ]
Starting MySQL-proxy...  :                                 [  OK  ]

数据库Master端

Master> create database proxy;         # 建个库
Query OK, 1 row affected (0.00 sec)Master> create table master(id int(2),name char(10));  # 停掉从库 IO线程后再建个表
Query OK, 0 rows affected (0.18 sec)Master> desc master;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id    | int(2)   | YES  |     | NULL    |       |
| name  | char(10) | YES  |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.00 sec)

Slave端

Slave> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| proxy              |     # 新建的库已经有了
| school             |
| test               |
+--------------------+
6 rows in set (0.00 sec)Slave> stop slave io_thread;      # 停掉 IO 线程
Query OK, 0 rows affected (0.00 sec)Slave> show slave status\G
*************************** 1. row ***************************Slave_IO_State: Master_Host: 192.168.0.88Master_User: repMaster_Port: 3306Connect_Retry: 60Master_Log_File: mysql-bin.000019Read_Master_Log_Pos: 351Relay_Log_File: relay-bin.000011Relay_Log_Pos: 497Relay_Master_Log_File: mysql-bin.000019Slave_IO_Running: NoSlave_SQL_Running: YesSlave> use proxy;
Database changedSlave> create table slave(id int(2),name char(10));  # 建个表
Query OK, 0 rows affected (0.00 sec)Slave> desc slave;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id    | int(2)   | YES  |     | NULL    |       |
| name  | char(10) | YES  |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.00 sec)Slave> insert into slave values(90,'slave');    # 插入一条数据
Query OK, 1 row affected (0.00 sec)Slave> select * from slave;
+------+-------+
| id   | name  |
+------+-------+
|   90 | slave |
+------+-------+
1 row in set (0.00 sec)

模拟远程连接MySQL-proxy服务器进行读写操作

[root@SQL-proxy ~]# mysql -h192.168.0.86 -uproxy -P3306 -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 12
Server version: 5.5.55-log MySQL Community Server (GPL)Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql>
mysql> use proxy;
Database changed
mysql>
mysql> show tables;   # show 出来的只有master这个表
+-----------------+
| Tables_in_proxy |
+-----------------+
| master          |
+-----------------+
1 row in set (0.01 sec)mysql> desc master;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id    | int(2)   | YES  |     | NULL    |       |
| name  | char(10) | YES  |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.00 sec)mysql> insert into master values(88,'master');  # 往master表里插入数据
Query OK, 1 row affected (0.00 sec)        <<--- 写入是 OK 的mysql> select * from master;
ERROR 1146 (42S02): Table 'proxy.master' doesn't exist  # 明显查不到的，因为去找从库了，从库上没有这表。mysql> show tables;   # 我们show时只能看到 master 表，好像show只能找主库。
+-----------------+
| Tables_in_proxy |
+-----------------+
| master          |
+-----------------+
1 row in set (0.00 sec)mysql> select * from slave;  # 我们直接查 slave 表
+------+-------+
| id   | name  |
+------+-------+
|   90 | slave |         <<--- 查到了，读操作成功
+------+-------+
1 row in set (0.00 sec)mysql>

恢复 slave IO 线程

Slave> start slave io_thread;
Query OK, 0 rows affected (0.00 sec)Slave> show slave status\G
*************************** 1. row ***************************Slave_IO_State: Waiting for master to send eventMaster_Host: 192.168.0.88Master_User: repMaster_Port: 3306Connect_Retry: 60Master_Log_File: mysql-bin.000019Read_Master_Log_Pos: 1566Relay_Log_File: relay-bin.000012Relay_Log_Pos: 1468Relay_Master_Log_File: mysql-bin.000019Slave_IO_Running: YesSlave_SQL_Running: Yes

再次模拟远程连接MySQL-proxy服务器查 master 表

[root@SQL-proxy ~]# mysql -h192.168.0.86 -uproxy -P3306 -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 12
Server version: 5.5.55-log MySQL Community Server (GPL)Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql>
mysql> use proxy;
Database changed
mysql>
mysql> select * from master;
+------+--------+
| id   | name   |
+------+--------+
|   88 | master |        <<----由于从库恢复后开始复制主库数据，所以可以查到了。
+------+--------+
1 row in set (0.00 sec)

以上MySQL-proxy读写分离完成。

存在的问题：

当模拟前端连接MySQL-proxy服务器并进行数据库操作时，MySQL-proxy服务器端屏幕有信息输出，不知道为什么？

信息如下：

[root@SQL-proxy ~]#     server default db: proxy

client default db: school

syncronizing

server default db: proxy

client default db: school

syncronizing

server default db: school

client default db: proxy

syncronizing