MySql之主从复制及读写分离

前言
使用MySQL Proxy和MySQL Replication实现读写分离

MySQL Replication可以将master的数据复制分布到多个slave上，然后可以利用slave来分担master的读压力。那么对于前台应用来说，就要考虑如何将读的压力分布到多个slave上。如果每个应用都需要来实现读写分离的算法，一则成本太高，二来如果slave增加更多的机器，应用就要随之修改。明显的，如果在应用和数据库间加一个专门用于实现读写分离的中间层，则整个系统的架构拥有更好的扩展性。MySQL Proxy就是这么一个中间层代理，简单的说，MySQL Proxy就是一个连接池，负责将前台应用的连接请求转发给后台的数据库，并且通过使用lua脚本，可以实现复杂的连接控制和过滤，从而实现读写分离和负载平衡。对于应用来说，MySQL Proxy是完全透明的，应用则只需要连接到MySQL Proxy的监听端口即可。当然，这样proxy机器可能成为单点失效，但完全可以使用多个proxy机器做为冗余，在应用服务器的连接池配置中配置到多个proxy的连接参数即可。

MySQL 5.6引入的GTID(Global Transaction IDs)使得其复制功能的配置、监控及管理变得更加易于实现，且更加健壮。
要在MySQL 5.6中使用复制功能，其服务配置段[mysqld]中于少应该定义如下选项：

binlog-format：二进制日志的格式，有row、statement和mixed几种类型；

需要注意的是：当设置隔离级别为READ-COMMITED必须设置二进制日志格式为ROW，现在MySQL官方认为STATEMENT这个已经不再适合继续使用；但mixed类型在默认的事务隔离级别下，可能会导致主从数据不一致；
log-slave-updates、gtid-mode、enforce-gtid-consistency、report-port和report-host：用于启动GTID及满足附属的其它需求；
master-info-repository和relay-log-info-repository：启用此两项，可用于实现在崩溃时保证二进制及从服务器安全的功能；
sync-master-info：启用之可确保无信息丢失；
slave-paralles-workers：设定从服务器的SQL线程数；0表示关闭多线程复制功能；
binlog-checksum、master-verify-checksum和slave-sql-verify-checksum：启用复制有关的所有校验功能；
binlog-rows-query-log-events：启用之可用于在二进制日志记录事件相关的信息，可降低故障排除的复杂度；
log-bin：启用二进制日志，这是保证复制功能的基本前提；
server-id：同一个复制拓扑中的所有服务器的id号必须惟一；

report-host：
The host name or IP address of the slave to be reported to the master during slave registration. This value appears in the output of SHOW SLAVE HOSTS on the master server.
report-port:

The TCP/IP port number for connecting to the slave, to be reported to the master during slave registration.
master-info-repository:

The setting of this variable determines whether the slave logs master status and connection information to a FILE (master.info), or to a TABLE (mysql.slave_master_info)
relay-log-info-repository：

This option causes the server to log its relay log info to a file or a table.
log_slave_updates：

Whether updates received by a slave server from a master server should be logged to the slave's own binary log. Binary logging must be enabled on the slave for this variable to have any effect.
enforce_gtid_consistency：

一、简单主从模式配置步骤
1、配置主从节点的服务配置文件
1.1、配置master节点：

[mysqld]
binlog-format=ROW
log-bin=master-bin
log-slave-updates=true
gtid-mode=on
enforce-gtid-consistency=true
master-info-repository=TABLE
relay-log-info-repository=TABLE
sync-master-info=1
slave-parallel-workers=2
binlog-checksum=CRC32
master-verify-checksum=1
slave-sql-verify-checksum=1
binlog-rows-query-log_events=1
server-id=1
report-port=3306
port=3306
datadir=/mydata/data
socket=/tmp/mysql.sock
report-host=master.xxx.com

1.2、配置slave节点

[mysqld]
binlog-format=ROW
log-slave-updates=true
gtid-mode=on
enforce-gtid-consistency=true
master-info-repository=TABLE
relay-log-info-repository=TABLE
sync-master-info=1
slave-parallel-workers=2
binlog-checksum=CRC32
master-verify-checksum=1
slave-sql-verify-checksum=1
binlog-rows-query-log_events=1
server-id=11
report-port=3306
port=3306
log-bin=mysql-bin.log
datadir=/mydata/data
socket=/tmp/mysql.sock
report-host=slave.xxx.com

2、创建复制用户

mysql>GRANT REPLICATION SLAVE ON *.* TO repluser@172.16.100.7 IDENTIFIED BY 'replpass';

说明：172.16.100.7是从节点服务器；如果想一次性授权更多节点，可以自行根据需要修改；

3、为备节点提供初始数据集
锁定主表，备份主节点上的数据，将其还原至从节点；如果没有启用GTID，在备份时需要在master使用show master status命令查看二进制日志文件名称及事件位置，以便后面启动slave节点时使用。
4、启动从节点的复制线程
如果启用了GTID功能，则使用如下命令：

mysql> CHANGE MASTER TO MASTER_HOST='master.xxx.com', MASTER_USER='repluser', MASTER_PASSWORD='replpass', MASTER_AUTO_POSITION=1;

没启用GTID，需要使用如下命令：

slave> CHANGE MASTER TO MASTER_HOST='172.16.100.6',
-> MASTER_USER='repluser',
-> MASTER_PASSWORD='replpass',
-> MASTER_LOG_FILE='master-bin.000003',
-> MASTER_LOG_POS=1174;

二、半同步复制

1、分别在主从节点上安装相关的插件

master> INSTALL PLUGIN rpl_semi_sync_master SONAME 'semisync_master.so';
slave> INSTALL PLUGIN rpl_semi_sync_slave SONAME 'semisync_slave.so';

2、启用半同步复制

在master上的配置文件中，添加

rpl_semi_sync_master_enabled=ON

在至少一个slave节点的配置文件中添加

rpl_semi_sync_slave_enabled=ON

而后重新启动mysql服务即可生效。

或者，也可以mysql服务上动态启动其相关功能：

master> SET GLOBAL rpl_semi_sync_master_enabled = ON;
slave> SET GLOBAL rpl_semi_sync_slave_enabled = ON;
slave> STOP SLAVE IO_THREAD; START SLAVE IO_THREAD;

3、确认半同步功能已经启用

master> CREATE DATABASE magedudb;
master> SHOW STATUS LIKE 'Rpl_semi_sync_master_yes_tx';
slave> SHOW DATABASES;

三、MySQL Proxy

1、源码安装时，Mysql proxy的依赖关系：
libevent 1.x or higher(1.3b or later is preferred).

lua 5.1.x or higher.
glib2 2.6.0 or higher.
pkg-config.
libtool 1.5 or higher.
MySQL 5.0.x or higher developer files.
2、安装

# tar zxf mysql-proxy-0.8.2.tar.gz

# cd mysql-proxy-0.8.2
# ./configure
# make

# make check
如果管理员有密码，上面的步骤则需要使用如下格式进行：

#MYSQL_PASSWORD=root_pwd make check
#make install
默认情况下，mysql-proxy安装在/usr/local/sbin/mysql-proxy，而Lua示例脚本安装在/usr/local/share目录中。
3、配置指令
mysql proxy的各配置参数请参见官方文档，http:.//dev.mysql.com/doc/refman/5.6/en/mysql-proxy-configuration.html

使用rpm包在rhel6上安装mysql-proxy-0.8.2，其会提供配置文件及服务脚本，但没有提供读写分享的脚本。

/etc/sysconfig/mysql-proxy文件用于定义mysql-proxy的启动参数。

ADMIN_USER – the user for the proxy's admin interface. You can leave the default admin user.
ADMIN_PASSWORD – the password for the admin user in clear text. Change the default password for better security.
ADMIN_LUA_SCRIPT – the admin script in the Lua programming language. Without this script the admin interface cannot work. You can leave the default value.
PROXY_USER – the system user under which the proxy will work. By default it is mysql-proxy, and it's safe to leave it as is.
PROXY_OPTIONS – proxy options such as logging level, plugins, and Lua scripts to be loaded.

其中PROXY_OPTIONS是最常用的一个选项，用于定义mysql-proxy工作时的重要参数，例如：
PROXY_OPTIONS="--daemon --log-level=info --log-use-syslog --plugins=proxy --plugins=admin --proxy-backend-addresses=192.168.1.102:3306 --proxy-read-only-backend-addresses=192.168.1.105:3306 --proxy-lua-script=/usr/lib/mysql-proxy/lua/proxy/rw-splitting.lua"
四、安装配置mysql-proxy
4.1 下载所需要的版本，这里的系统平台为rhel6.4 32位系统，因此就以mysql-proxy-0.8.3-linux-glibc2.3-x86-32bit.tar.gz为例。

# tar xf mysql-proxy-0.8.3-linux-glibc2.3-x86-32bit.tar.gz -C /usr/local
# cd /usr/local
# ln -sv mysql-proxy-0.8.3-linux-glibc2.3-x86-32bit  mysql-proxy

添加代理用户

# useradd mysql-proxy

4.2 为mysql-proxy提供SysV脚本，内容如下所示

#!/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

将上述内容保存为/etc/rc.d/init.d/mysql-proxy，给予执行权限，而后加入到服务列表。

# chmod +x /etc/rc.d/init.d/mysql-proxy
# chkconfig --add mysql-proxy

4.3 为服务脚本提供配置文件/etc/sysconfig/mysql-proxy,内容如下所示：

# 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"

其中最后一行，需要按实际场景进行修改，例如：

PROXY_OPTIONS="--daemon --log-level=info --log-use-syslog --plugins=proxy --plugins=admin --proxy-backend-addresses=172.16.100.6:3306 --proxy-read-only-backend-addresses=172.16.100.7:3306 --proxy-lua-script=/usr/local/mysql-proxy/share/doc/mysql-proxy/rw-splitting.lua"

其中的proxy-backend-addresses选项和proxy-read-only-backend-addresses选项均可重复使用多次，以实现指定多个读写服务器或只读服务器。

4.4 mysql-proxy的配置选项
mysql-proxy的配置选项大致可分为帮助选项、管理选项、代理选项及应用程序选项几类，下面一起去介绍他们。

--help
--help-admin
--help-proxy
--help-all ———— 以上四个选项均用于获取帮助信息；
--proxy-address=host:port ———— 代理服务监听的地址和端口；
--admin-address=host:port ———— 管理模块监听的地址和端口；
--proxy-backend-addresses=host:port ———— 后端mysql服务器的地址和端口；
--proxy-read-only-backend-addresses=host:port ———— 后端只读mysql服务器的地址和端口；
--proxy-lua-script=file_name ———— 完成mysql代理功能的Lua脚本；
--daemon ———— 以守护进程模式启动mysql-proxy；
--keepalive ———— 在mysql-proxy崩溃时尝试重启之；
--log-file=/path/to/log_file_name ———— 日志文件名称；
--log-level=level ———— 日志级别；
--log-use-syslog ———— 基于syslog记录日志；
--plugins=plugin,.. ———— 在mysql-proxy启动时加载的插件；
--user=user_name ———— 运行mysql-proxy进程的用户；
--defaults-file=/path/to/conf_file_name ———— 默认使用的配置文件路径；其配置段使用[mysql-proxy]标识；
--proxy-skip-profiling ———— 禁用profile；
--pid-file=/path/to/pid_file_name ———— 进程文件名；

5、复制如下内容建立admin.lua文件，将其保存至/usr/local/mysql-proxy/share/doc/mysql-proxy/目录中。。

--[[ $%BEGINLICENSE%$
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

6、测试
6.1 管理功能测试

# mysql -uadmin -padmin -h172.16.100.107 --port=4041

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.0.99-agent-admin
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.
mysql> SELECT * FROM backends;
+-------------+-------------------+-------+------+------+-------------------+
| backend_ndx | address           | state | type | uuid | connected_clients |
+-------------+-------------------+-------+------+------+-------------------+
|           1 | 172.16.100.6:3306 | up    | rw   | NULL |                 0 |
|           2 | 172.16.100.7:3306 | up    | ro   | NULL |                 0 |
+-------------+-------------------+-------+------+------+-------------------+
2 rows in set (0.00 sec)

6.2 读写分离测试

# mysql -uroot -pXXX.com -h172.16.100.107 --port=4040