Mysql的读写分离可以使用MySQL Proxy和Amoeba实现，其实也可以使用MySQL-MMM实现读写分离的自动切换。MySQL Proxy有一项强大功能是实现"读写分离"，基本原理是让主数据库处理写方面事务，让从库处理SELECT查询；Amoeba for MySQL是一款优秀的中间件软件，同样可以实现读写分离，负载均衡等功能。下面重点说下Mysql Proxy:
MySQL Proxy处于客户端应用程序和MySQL服务器之间，通过截断、改变并转发客户端和后端数据库之间的通信来实现其功能。代理服务器是和TCP/IP协议打交道， 而要理解MySQL Proxy的工作机制，同样要清楚MySQL客户端和服务器之间的通信协议，MySQL Protocol 包括认证和查询两个基本过程： ................................. 认证过程包括： 1）客户端向服务器发起连接请求 2）服务器向客户端发送握手信息 3）客户端向服务器发送认证请求 4）服务器向客户端发送认证结果 ................................ 如果认证通过，则进入查询过程： 1）客户端向服务器发起查询请求 2）服务器向客户端返回查询结果 当然，这只是一个粗略的描述，每个过程中发送的包都是有固定格式的。MySQL Proxy要做的，就是介入协议的各个过程。首先MySQL Proxy以服务器的身份接受客户端请求， 根据配置对这些请求进行分析处理，然后以客户端的身份转发给相应的后端数据库服务器，再接受服务器的信息，返回给客户端。所以MySQL Proxy需要同时实现客户端和服务 器的协议。由于要对客户端发送过来的SQL语句进行分析，还需要包含一个SQL解析器。可以说MySQL Proxy相当于一个轻量级的MySQL了，实际上，MySQL Proxy的admin server 是可以接受SQL来查询状态信息的。 MySQL Proxy通过lua 脚本来控制连接转发的机制。主要的函数都是配合MySQL Protocol各个过程的，这一点从函数名上就能看出来： connect_server() read_handshake() read_auth() read_auth_result() read_query() read_query_result() 至于为什么采用lua 脚本语言，大概是因为MySQL Proxy中采用了wormhole 存储引擎 的关系吧，这个虫洞存储引擎很有意思，数据的存储格式就是一段lua脚本。
Mysql Proxy的原理图
顺便贴下Mysql Proxy的工作拓扑图
部署MySQL Proxy实现读写分离并提高并发负载的操作记录
0）机器环境
ip地址 角色 主机名 182.48.115.237 master master-node 182.48.115.236 slave1 slave-node1 182.48.115.238 slave2 slave-node2 182.48.115.233 proxy proxy-node 四台机器都关闭防火墙和selinux 绑定hosts设置（四台机器都要操作） [root@master-node ~]# vim /etc/hosts ...... 182.48.115.237 master-node 182.48.115.236 slave-node1 182.48.115.238 slave-node2 182.48.115.233 proxy-node
1）Mysql主从复制部署（在三台mysql节点机上部署，本案例是一主两从架构）
mysql安装参考：http://www.cnblogs.com/kevingrace/p/6109679.html mysql主从部署参考：http://www.cnblogs.com/kevingrace/p/6256603.html
2）在proxy机器上安装mysql-proxy
1）安装mysql-proxy
mysql proxy实现读写分离是有lua脚本实现的
下载地址1：https://downloads.mysql.com/archives/proxy/#downloads
下载地址2: http://ftp.ntu.edu.tw/pub/MySQL/Downloads/MySQL-Proxy/
[root@proxy-node ~]# wget http://ftp.ntu.edu.tw/pub/MySQL/Downloads/MySQL-Proxy/mysql-proxy-0.8.5-linux-el6-x86-64bit.tar.gz
[root@proxy-node ~]# tar -zvxf mysql-proxy-0.8.5-linux-el6-x86-64bit.tar.gz
[root@proxy-node ~]# mv mysql-proxy-0.8.5-linux-el6-x86-64bit /usr/local/mysql-proxy
[root@proxy-node ~]# useradd -r mysql-proxy
2）提供服务脚本
[root@proxy-node ~]# 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/functions
prog="/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 0
# Set default mysql-proxy configuration.
ADMIN_USER="admin"
ADMIN_PASSWD="admin"
ADMIN_LUA_SCRIPT="/usr/local/mysql-proxy/share/doc/mysql-proxy/admin.lua"
PROXY_OPTIONS="--daemon"
PROXY_PID=/var/run/mysql-proxy.pid
PROXY_USER="mysql-proxy"
# Source mysql-proxy configuration.
if [ -f /etc/sysconfig/mysql-proxy ]; then
. /etc/sysconfig/mysql-proxy
fi
RETVAL=0
start() {
echo -n $"Starting $prog: "
daemon $prog $PROXY_OPTIONS --pid-file=$PROXY_PID --proxy-address="$PROXY_ADDRESS" --user=$PROXY_USER --admin-username="$ADMIN_USER" --admin-lua-script="$ADMIN_LUA_SCRIPT" --admin-password="$ADMIN_PASSWORD"
RETVAL=$?
echo
if [ $RETVAL -eq 0 ]; then
touch /var/lock/subsys/mysql-proxy
fi
}
stop() {
echo -n $"Stopping $prog: "
killproc -p $PROXY_PID -d 3 $prog
RETVAL=$?
echo
if [ $RETVAL -eq 0 ]; then
rm -f /var/lock/subsys/mysql-proxy
rm -f $PROXY_PID
fi
}
# See how we were called.
case "$1" in
start)
start
;;
stop)
stop
;;
restart)
stop
start
;;
condrestart|try-restart)
if status -p $PROXY_PIDFILE $prog >&/dev/null; then
stop
start
fi
;;
status)
status -p $PROXY_PID $prog
;;
*)
echo "Usage: $0 {start|stop|restart|reload|status|condrestart|try-restart}"
RETVAL=1
;;
esac
exit $RETVAL
[root@proxy-node ~]# chmod 755 /etc/init.d/mysql-proxy
[root@proxy-node ~]# chkconfig --add mysql-proxy
3）为服务脚本提供配置文件
[root@proxy-node ~]# vim /etc/sysconfig/mysql-proxy
# Options for mysql-proxy
ADMIN_USER="admin"
ADMIN_PASSWORD="admin"
ADMIN_ADDRESS=""
ADMIN_LUA_SCRIPT="/usr/local/mysql-proxy/share/doc/mysql-proxy/admin.lua"
PROXY_ADDRESS=""
PROXY_USER="mysql-proxy"
PROXY_OPTIONS="--daemon --log-level=info --log-use-syslog --plugins=proxy --plugins=admin --proxy-backend-addresses=182.48.115.237:3306 --proxy-read-only-backend-addresses=182.48.115.236:3306
--proxy-read-only-backend-addresses=182.48.115.238:3306 --proxy-lua-script=/usr/local/mysql-proxy/share/doc/mysql-proxy/rw-splitting.lua"
配置参数解释：
--daemon：以守护进程模式启动mysql-proxy
--proxy-backend-addresses：后端可读写的mysql服务器的地址和端口
--proxy-read-only-backend-addresses：后端只读mysql服务器的地址和端口
--proxy-lua-script：完成mysql代理功能的Lua脚本
4）提供admin.lua文件
[root@proxy-node ~]# vim /usr/local/mysql-proxy/share/doc/mysql-proxy/admin.lua
--[[ $%BEGINLICENSE%$
Copyright (c) 2007, 2012, Oracle and/or its affiliates. All rights reserved.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; version 2 of the
License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
02110-1301 USA
$%ENDLICENSE%$ --]]
function set_error(errmsg)
proxy.response = {
type = proxy.MYSQLD_PACKET_ERR,
errmsg = errmsg or "error"
}
end
function read_query(packet)
if packet:byte() ~= proxy.COM_QUERY then
set_error("[admin] we only handle text-based queries (COM_QUERY)")
return proxy.PROXY_SEND_RESULT
end
local query = packet:sub(2)
local rows = { }
local fields = { }
if query:lower() == "select * from backends" then
fields = {
{ name = "backend_ndx",
type = proxy.MYSQL_TYPE_LONG },
{ name = "address",
type = proxy.MYSQL_TYPE_STRING },
{ name = "state",
type = proxy.MYSQL_TYPE_STRING },
{ name = "type",
type = proxy.MYSQL_TYPE_STRING },
{ name = "uuid",
type = proxy.MYSQL_TYPE_STRING },
{ name = "connected_clients",
type = proxy.MYSQL_TYPE_LONG },
}
for i = 1, #proxy.global.backends do
local states = {
"unknown",
"up",
"down"
}
local types = {
"unknown",
"rw",
"ro"
}
local b = proxy.global.backends[i]
rows[#rows + 1] = {
i,
b.dst.name, -- configured backend address
states[b.state + 1], -- the C-id is pushed down starting at 0
types[b.type + 1], -- the C-id is pushed down starting at 0
b.uuid, -- the MySQL Server's UUID if it is managed
b.connected_clients -- currently connected clients
}
end
elseif query:lower() == "select * from help" then
fields = {
{ name = "command",
type = proxy.MYSQL_TYPE_STRING },
{ name = "description",
type = proxy.MYSQL_TYPE_STRING },
}
rows[#rows + 1] = { "SELECT * FROM help", "shows this help" }
rows[#rows + 1] = { "SELECT * FROM backends", "lists the backends and their state" }
else
set_error("use 'SELECT * FROM help' to see the supported commands")
return proxy.PROXY_SEND_RESULT
end
proxy.response = {
type = proxy.MYSQLD_PACKET_OK,
resultset = {
fields = fields,
rows = rows
}
}
return proxy.PROXY_SEND_RESULT
end
5）为了测试更明显，编辑rw-splitting.lua文件中的其中2个数值：
[root@proxy-node ~]# vim /usr/local/mysql-proxy/share/doc/mysql-proxy/rw-splitting.lua
.........
if not proxy.global.config.rwsplit then
proxy.global.config.rwsplit = {
min_idle_connections = 1, //修改这个值，默认为4
max_idle_connections = 1, //修改这个值，默认为8
is_debug = false
}
end
........
注意：
mysql-proxy会检测客户端连接，当连接没有超过min_idle_connections预设值时, 不会进行读写分离, 即查询操作会发生到Master上。
6）启动mysql-proxy
[root@proxy-node ~]# service mysql-proxy start
Starting /usr/local/mysql-proxy/bin/mysql-proxy: [ OK ]
[root@proxy-node ~]# service mysql-proxy status
mysql-proxy (pid 4655) is running...
[root@proxy-node ~]# netstat -tunlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:4041 0.0.0.0:* LISTEN 4655/mysql-proxy
tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN 4655/mysql-proxy
7）连接测试（在任意一台远程客户机上测试连接）
[root@slave-node2 ~]# mysql -uadmin -padmin -h182.48.115.233 --port=4041
Warning: Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.0.99-agent-admin
Copyright (c) 2000, 2016, 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> SELECT * FROM backends;
+-------------+---------------------+---------+------+------+-------------------+
| backend_ndx | address | state | type | uuid | connected_clients |
+-------------+---------------------+---------+------+------+-------------------+
| 1 | 182.48.115.237:3306 | unknown | rw | NULL | 0 |
| 2 | 182.48.115.236:3306 | unknown | ro | NULL | 0 |
| 3 | 182.48.115.238:3306 | unknown | ro | NULL | 0 |
+-------------+---------------------+---------+------+------+-------------------+
3 rows in set (0.00 sec)
3）读写分离测试
1）在master-node数据库上创建proxy用户，从服务器也会同步这个操作。 mysql> GRANT ALL ON *.* TO 'wang'@'182.48.115.%' IDENTIFIED BY '123456'; Query OK, 0 rows affected (0.00 sec) mysql> flush privileges; Query OK, 0 rows affected (0.00 sec) 2）proxy-node机器上使用创建的proxy用户登陆数据库，进行数据操作 [root@proxy-node ~]# mysql -uwang -h182.48.115.233 -p123456 ....... mysql> create database huanqiutest; Query OK, 1 row affected (0.00 sec) mysql> use huanqiutest; Database changed mysql> create table haha( id int(5), name varchar(10)); Query OK, 0 rows affected (0.19 sec) mysql> insert into haha values(1,"zhangbao"); Query OK, 1 row affected (0.00 sec) mysql> insert into haha values(11,"shibo"); Query OK, 1 row affected (0.00 sec) mysql> select * from haha; +------+----------+ | id | name | +------+----------+ | 1 | zhangbao | | 11 | shibo | +------+----------+ 2 rows in set (0.01 sec) 注意下面两点： -> 发现使用proxy用户登陆数据库写入的数据只写入master主库，然后再同步到slave从库。如果将从库的slave同步功能关闭，则从库就无法更新数据。 -> 登陆从库服务器关闭slave同步功能（stop slave），这时再登陆proxy-noed机器肯定会查询不出数据（能看到表，但是查询不出数据） -> 以上两点真正实现了读写分离的效果！ 3）查看状态，在proxy-node机器上操作，可以看到状态全部为up： [root@proxy-node bin]# mysql -uadmin -padmin -h182.48.115.233 --port=4041 ....... mysql> SELECT * FROM backends; +-------------+---------------------+---------+------+------+-------------------+ | backend_ndx | address | state | type | uuid | connected_clients | +-------------+---------------------+---------+------+------+-------------------+ | 1 | 182.48.115.237:3306 | up | rw | NULL | 0 | | 2 | 182.48.115.236:3306 | up | ro | NULL | 0 | | 3 | 182.48.115.238:3306 | up | ro | NULL | 0 | +-------------+---------------------+---------+------+------+-------------------+ 3 rows in set (0.00 sec)
读写分离，延迟是个大问题，要确保主从同步这一环节不要有延迟。
---------------mysql主从同步延迟原理----------------
－> mysql主从同步原理
主库针对读写操作，顺序写 binlog，从库单线程去主库读"写操作的binlog",从库取到 binlog在本地原样执行(随机写),来保证主从数据逻辑上一致.
mysql的主从复制都是单线程的操作，主库对所有DDL和DML产生 binlog，binlog是顺序写，所以效率很高，slave的Slave_IO_Running线程到主库取日志，效率比较高，下一步问题来了，slave的 slave_sql_running线程将主库的 DDL和DML操作在 slave实施。DML，DDL的IO操作是随即的，不能顺序的，成本高很多，还有可能slave上的其他查询产生 lock，由于 slave_sql_running也是单线程的，所以 一个 DDL卡住了，需求需求执行一段时间，那么所有之后的DDL会等待这个 DDL执行完才会继续执行，这就导致了延迟.由于master可以并发，Slave_sql_running线程却不可以，所以主库执行 DDL需求一段时间，在slave执行相同的DDL时，就产生了延迟.
-> 主从同步延迟产生原因
当主库的TPS并发较高时，产生的DDL数量超过Slave一个 sql线程所能承受的范围，那么延迟就产生了，当然还有就是可能与 slave的大型 query语句产生了锁等待
首要原因：数据库在业务上读写压力太大，CPU计算负荷大，网卡负荷大，硬盘随机IO太高
次要原因：读写 binlog带来的性能影响，网络传输延迟
-> mysql主从同步加速
1）sync_binlog在slave端设置为0
2）–logs-slave-updates 从服务器从主服务器接收到的更新不记入它的二进制日志。
3）直接禁用slave端的binlog
4）slave端，如果使用的存储引擎是innodb，innodb_flush_log_at_trx_commit =2
再有就是进行分库分表处理，这样减少数据量的复制同步操作
