一 什麼是讀寫分離
MySQL Proxy最強大的一項功能是實現“讀寫分離(Read/Write Splitting)”。基本的原理是讓主數據庫處理事務性查詢，而從數據庫處理SELECT查詢。數據庫復制被用來把事務性查詢導致的變更同步到集群中的從數據庫。 當然，主服務器也可以提供查詢服務。使用讀寫分離最大的作用無非是環境服務器壓力。可以看下這張圖：
MySQL 讀寫分離示意圖
二 讀寫分離的好處
•增加冗余
•增加了機器的處理能力
•對於讀操作為主的應用，使用讀寫分離是最好的場景，因為可以確保寫的服務器壓力更小，而讀又可以接受點時間上的延遲。
三 讀寫分離提高性能之原因
•物理服務器增加，負荷增加
•主從只負責各自的寫和讀，極大程度的緩解X鎖和S鎖爭用
•從庫可配置myisam引擎，提升查詢性能以及節約系統開銷
•從庫同步主庫的數據和主庫直接寫還是有區別的，通過主庫發送來的binlog恢復數據，但是，最重要區別在於主庫向從庫發送binlog是異步的，從庫恢復數據也是異步的
•讀寫分離適用與讀遠大於寫的場景，如果只有一台服務器，當select很多時，update和delete會被這些select訪問中的數據堵塞，等待select結束，並發性能不高。 對於寫和讀比例相近的應用，應該部署雙主相互復制
•可以在從庫啟動是增加一些參數來提高其讀的性能，例如–skip-innodb、–skip-bdb、–low-priority-updates以及–delay-key-write=ALL。當然這些設置也是需要根據具體業務需求來定得，不一定能用上
•分攤讀取。假如我們有1主3從，不考慮上述1中提到的從庫單方面設置，假設現在1分鐘內有10條寫入，150條讀取。那麼，1主3從相當於共計40條寫入，而讀取總數沒變，因此平均下來每台服務器承擔了10條寫入和50條讀取（主庫不承擔讀取操作）。因此，雖然寫入沒變，但是讀取大大分攤了，提高了系統性能。另外，當讀取被分攤後，又間接提高了寫入的性能。所以，總體性能提高了，說白了就是拿機器和帶寬換性能。MySQL官方文檔中有相關演算公式：官方文檔 見6.9FAQ之“MySQL復制能夠何時和多大程度提高系統性能”
•MySQL復制另外一大功能是增加冗余，提高可用性，當一台數據庫服務器宕機後能通過調整另外一台從庫來以最快的速度恢復服務，因此不能光看性能，也就是說1主1從也是可以的。
四 讀寫分離示意圖
讀寫分離示意圖
五 讀寫分離模擬
實驗環境簡介
主機
IP地址
主機名
備注
serv01 192.168.1.11 serv01.host.com 代理服務器
serv08 192.168.1.18 serv08.host.com 主服務器（主要寫數據，可讀可寫）
serv09 192.168.1.19 serv09.host.com 從服務器（主要讀數據）
操作系統版本
RHEL Server6.1 64位系統
使用到的軟件包版本
•mysql-5.5.29-linux2.6-x86_64.tar.gz
•mysql-proxy-0.8.2-linux-glibc2.3-x86-64bit.tar.gz
第一步，搭建MySQL服務器，清空日志。注意：代理服務器中不需要裝MySQL。
第二步，拷貝mysql-proxy-0.8.2-linux-glibc2.3-x86-64bit.tar.gz文件，解壓文件。
scp mysql-proxy-0.8.2-linux-glibc2.3-x86-64bit.tar.gz 192.168.1.11:/opt
tar -xvf mysql-proxy-0.8.2-linux-glibc2.3-x86-64bit.tar.gz -C /usr/local/
cd /usr/local/
mv mysql-proxy-0.8.2-linux-glibc2.3-x86-64bit/ mysql-proxy
ll mysql-proxy/
# 可以查看幫助
./mysql-proxy --help-all
第三步，serv08主服務器創建用戶，serv09從服務器創建用戶，注意用戶名和密碼一致。
--serv08
mysql> grant all on *.* to 'larry'@'192.168.1.%' identified by 'larry';
Query OK, 0 rows affected (0.00 sec)
--serv09
mysql> grant all on *.* to 'larry'@'192.168.1.%' identified by 'larry';
Query OK, 0 rows affected (0.00 sec)
第四步，serv09從服務器更改設置，開啟slave，查看slave狀態。創建測試數據庫，插入測試數據。
--serv09
mysql> change master to \
master_host='192.168.1.18', \
master_user='larry', \
master_password='larry', \
master_port=3306, \
master_log_file='mysql-bin.000001', \
master_log_pos=107;
Query OK, 0 rows affected (0.01 sec)
mysql> start slave;
Query OK, 0 rows affected (0.00 sec)
mysql> show slave status \G;
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.1.18
Master_User: larry
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000001
Read_Master_Log_Pos: 107
Relay_Log_File: serv09-relay-bin.000002
Relay_Log_Pos: 253
Relay_Master_Log_File: mysql-bin.000001
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno: 0
Last_Error:
Skip_Counter: 0
Exec_Master_Log_Pos: 107
Relay_Log_Space: 410
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 2
1 row in set (0.00 sec)
ERROR:
No query specified
mysql> select user,password,host from mysql.user;
mysql> create database larrydb;
Query OK, 1 row affected (0.00 sec)
mysql> use larrydb;
Database changed
mysql> create table user(id int, name varchar(30));
Query OK, 0 rows affected (0.01 sec)
mysql> insert into user values(1,'larrywen');
Query OK, 1 row affected (0.01 sec)
mysql> insert into user values(2,'wentasy');
Query OK, 1 row affected (0.00 sec)
mysql> select * from user;
+------+----------+
| id | name |
+------+----------+
| 1 | larrywen |
| 2 | wentasy |
+------+----------+
2 rows in set (0.00 sec)
serv09
mysql> select * from larrydb.user;
+------+----------+
| id | name |
+------+----------+
| 1 | larrywen |
| 2 | wentasy |
+------+----------+
2 rows in set (0.00 sec)
第五步，為了查看現象，serv09從服務器關閉slave。
mysql> stop slave;
Query OK, 0 rows affected (0.01 sec)
第六步，serv 01查看是否有MySQL用戶，修改rw-splitting.lua文件，修改如下幾個參數。
id mysql
vim rw-splitting.lua
cat rw-splitting.lua | grep -e min_idle_connections -e max_idle_connections -e is_debug
min_idle_connections = 1,--最小空閒連接數，為了測試，這裡設置為1
max_idle_connections = 1,--最大空閒連接數，為了測試，這裡設置為1
is_debug = true--是否打開Debug調試，為了查看調試信息，這裡設置為true
第七步，啟動mysql-proxy。
/etc/init.d/mysql-proxy start
Starting mysql-proxy:
先確定是否可以連接。
mysql -ularry -plarry -h 192.168.1.18
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 6
Server version: 5.5.29-log Source distribution
mysql> exit
Bye
mysql -ularry -plarry -h 192.168.1.19
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 5.5.29-log Source distribution
mysql> exit
Bye
第八步，查看現象。
/etc/init.d/mysql-proxy start
Starting mysql-proxy:
mysql -ularry -plarry -h 192.168.1.11
[connect_server] 192.168.1.11:51054
[1].connected_clients = 0
[1].pool.cur_idle = 0
[1].pool.max_idle = 1
[1].pool.min_idle = 1
[1].type = 1
[1].state = 0
[1] idle-conns below min-idle
Welcome to the MySQL monitor. Commands end with ; or \g.
[read_query] 192.168.1.11:51054
current backend = 0
client default db =
client username = larry
query = select @@version_comment limit 1
sending to backend : 192.168.1.19:3306
is_slave : false
server default db:
server username : larry
in_trans : false
in_calc_found : false
COM_QUERY : true
Your MySQL connection id is 10
mysql> use larrydb;
[read_query] 192.168.1.11:51054
current backend = 0
client default db =
client username = larry
query = SELECT DATABASE()
sending to backend : 192.168.1.19:3306
is_slave : false
server default db:
server username : larry
in_trans : false
in_calc_found : false
COM_QUERY : true
[read_query] 192.168.1.11:51054
current backend = 0
client default db =
client username = larry
sending to backend : 192.168.1.19:3306
is_slave : false
server default db:
server username : larry
in_trans : false
in_calc_found : false
COM_QUERY : false
Database changed
mysql> select * from user;
[read_query] 192.168.1.11:51054
current backend = 0
client default db = larrydb
client username = larry
query = select * from user
sending to backend : 192.168.1.19:3306
is_slave : false
server default db: larrydb
server username : larry
in_trans : false
in_calc_found : false
COM_QUERY : true
+------+----------+
| id | name |
+------+----------+
| 1 | larrywen |
| 2 | wentasy |
+------+----------+
2 rows in set (0.00 sec)
mysql> insert into user values(3,'jsutdb');
[read_query] 192.168.1.11:51644
current backend = 0
client default db = larrydb
client username = larry
query = insert into user values(3,'jsutdb')
sending to backend : 192.168.1.19:3306
is_slave : false
server default db: larrydb
server username : larry
in_trans : false
in_calc_found : false
COM_QUERY : true
Query OK, 1 row affected (0.00 sec)
查看數據。
--serv08
mysql> select * from user;
+------+----------+
| id | name |
+------+----------+
| 1 | larrywen |
| 2 | wentasy |
+------+----------+
2 rows in set (0.00 sec)
--serv09
mysql> select * from larrydb.user;
+------+----------+
| id | name |
+------+----------+
| 1 | larrywen |
| 2 | wentasy |
| 3 | jsutdb |
+------+----------+
3 rows in set (0.00 sec)
第九步，以上的測試雖有效果，但不是預期。排查原因，重新配置。發現proxy-read-only-backend-addresses和proxy-backend-addresses參數配置出錯，proxy-read-only-backend-addresses應該配置成從服務器的IP地址，proxy-backend-addresses應該配置成主服務器的IP地址。
vim /etc/init.d/mysql-proxy
cat /etc/init.d/mysql-proxy
腳本內容如下：
#!/bin/sh
#
# mysql-proxy This script starts and stops the mysql-proxy daemon
#
# chkconfig: - 78 30
# processname: mysql-proxy
# description: mysql-proxy is a proxy daemon to mysql
# Source function library.
. /etc/rc.d/init.d/functions
#PROXY_PATH=/usr/local/bin
PROXY_PATH=/usr/local/mysql-proxy/bin
prog="mysql-proxy"
# Source networking configuration.
. /etc/sysconfig/network
# Check that networking is up.
[ ${NETWORKING} = "no" ] && exit 0
# Set default mysql-proxy configuration.
#PROXY_OPTIONS="--daemon"
PROXY_OPTIONS="--proxy-read-only-backend-addresses=192.168.1.19:3306 \
--proxy-backend-addresses=192.168.1.18:3306 \
--proxy-lua-script=/usr/local/mysql-proxy/share/doc/mysql-proxy/rw-splitting.lua"
#PROXY_PID=/usr/local/mysql-proxy/run/mysql-proxy.pid
PROXY_PID=/var/run/mysql-proxy.pid
# Source mysql-proxy configuration.
if [ -f /etc/sysconfig/mysql-proxy ]; then
. /etc/sysconfig/mysql-proxy
fi
PATH=$PATH:/usr/bin:/usr/local/bin:$PROXY_PATH
# By default it's all good
RETVAL=0
# See how we were called.
case "$1" in
start)
# Start daemon.
echo -n $"Starting $prog: "
$NICELEVEL $PROXY_PATH/mysql-proxy $PROXY_OPTIONS \
--daemon \
--pid-file=$PROXY_PID \
--user=mysql \
--log-level=debug \
--log-file=/var/log/mysql-proxy.log \
--proxy-address=192.168.1.11:3306
RETVAL=$?
echo
if [ $RETVAL = 0 ]; then
touch /var/lock/subsys/mysql-proxy
fi
;;
stop)
# Stop daemons.
echo -n $"Stopping $prog: "
killproc $prog
RETVAL=$?
echo
if [ $RETVAL = 0 ]; then
rm -f /var/lock/subsys/mysql-proxy
rm -f $PROXY_PID
fi
;;
restart)
$0 stop
sleep 3
$0 start
;;
condrestart)
[ -e /var/lock/subsys/mysql-proxy ] && $0 restart
;;
status)
status mysql-proxy
RETVAL=$?
;;
*)
echo "Usage: $0 {start|stop|restart|status|condrestart}"
RETVAL=1
;;
esac
exit $RETVAL
第十步，測試。插入數據，可以發現連接的是主服務器，查詢的時候也是主服務器。說明主服務器和從服務器均有讀的的功能。
mysql -ularry -plarry -h 192.168.1.11
[connect_server] 192.168.1.11:57891
[1].connected_clients = 0
[1].pool.cur_idle = 0
[1].pool.max_idle = 1
[1].pool.min_idle = 1
[1].type = 1
[1].state = 1
[1] idle-conns below min-idle
[read_query] 192.168.1.11:57891
current backend = 0
client default db =
client username = larry
query = select @@version_comment limit 1
sending to backend : 192.168.1.18:3306
is_slave : false
server default db:
server username : larry
in_trans : false
in_calc_found : false
COM_QUERY : true
mysql> insert into user values(5,'test');
Query OK, 1 row affected (0.01 sec)
[read_query] 192.168.1.11:57893
current backend = 0
client default db = larrydb
client username = larry
query = insert into user values(5,'test')
sending to backend : 192.168.1.18:3306
is_slave : false
server default db: larrydb
server username : larry
in_trans : false
in_calc_found : false
COM_QUERY : true
mysql> select * from user;
+------+----------+
| id | name |
+------+----------+
| 1 | larrywen |
| 2 | wentasy |
| 5 | test |
+------+----------+
3 rows in set (0.00 sec)
[read_query] 192.168.1.11:57893
current backend = 0
client default db = larrydb
client username = larry
query = select * from user
sending to backend : 192.168.1.18:3306
is_slave : false
server default db: larrydb
server username : larry
in_trans : false
in_calc_found : false
COM_QUERY : true
serv08主服務器查看數據，可以查詢到，說明主服務器可以寫。
mysql> select * from larrydb.user;
+------+----------+
| id | name |
+------+----------+
| 1 | larrywen |
| 2 | wentasy |
| 5 | test |
+------+----------+
3 rows in set (0.00 sec)
serv09從服務器查詢數據，發現不可查詢到，說明從服務器只讀。
mysql> mysql> select * from larrydb.user;
+------+----------+
| id | name |
+------+----------+
| 1 | larrywen |
| 2 | wentasy |
| 3 | jsutdb |
| 4 | db |
+------+----------+
4 rows in set (0.00 sec)
第十一步，開啟slave。發現數據同步成功。
mysql> start slave;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from larrydb.user;
+------+----------+
| id | name |
+------+----------+
| 1 | larrywen |
| 2 | wentasy |
| 3 | jsutdb |
| 4 | db |
| 5 | test |
+------+----------+
5 rows in set (0.00 sec)
