memcached+magent实现负载
环境：
CentOS 5.4 x64
这里只用1台虚拟机的3个不同端口模拟，可以进一步模拟3台虚拟机的同一个端口实验
yum -y install gcc
mkdir -p /opt/{lnmp,packet_src}/
cd /opt/packet_src/
wget https://memcached.googlecode.com/files/memcached-1.4.15.tar.gz
wget http://sourceforge.net/projects/levent/files/libevent/libevent-1.4/libevent-1.4.13-stable.tar.gz/download
wget http://memagent.googlecode.com/files/magent-0.6.tar.gz
1、编译安装libevent：
tar zxvf libevent-1.4.13-stable.tar.gz
cd libevent-1.4.13-stable/
./configure --prefix=/usr
make && make install
cd ../
2、编译安装Memcached
tar zxvf memcached-1.4.15.tar.gz
cd memcached-1.4.15/
./configure --prefix=/opt/lnmp/memcached/ --with-libevent=/usr
make && make install
cd ../
参数手册
启动过程中所用选项说明如下：
-p，使用的TCP端口。默认为11211。
-m，最大内存大小。默认为64MB。
-vv，以very vrebose模式启动，将调试信息和错误输出到控制台。
-d，作为守护进程在后台运行。
-c，最大运行的并发连接数，默认是1024，按照服务器的负载量来设定。
-P，设置保存Memcache的pid文件。
-l，监听的服务器IP地址，如果有多个地址。
-u，运行Memcached的用户，默认不能由root用户启动，所以当前用户为root用户时，需要利用-u参数来指定。
例：/opt/lnmp/memcached/bin/memcached -m 32m -d -l 192.168.4.222 -p 11211 -u root -P /opt/lnmp/memcached/memcached_11211.pid -c 256
3、编译安装magent：
mkdir -p magent
tar zxvf magent-0.6.tar.gz -C magent
/sbin/ldconfig
sed -i "s#LIBS = -levent#LIBS = -levent -lm#g" Makefile //版本小于0.6需要执行这一句
make
cp magent /usr/bin/magent
Usage:
-h this message
-u uid
-g gid
-p port, default is 11211. (0 to disable tcp support)
-s ip:port, set memcached server ip and port
-b ip:port, set backup memcached server ip and port
-l ip, local bind ip address, default is 0.0.0.0
-n number, set max connections, default is 4096
-D do not go to background
-k use ketama key allocation algorithm
-f file, unix socket path to listen on. default is off
-i number, max keep alive connections for one memcached server, default is 20
问题：
gcc: /usr/lib64/libevent.a: No such file or directory
解决办法：
ln -s /usr/lib/libevent.a /usr/lib64/libevent.a
问题：
gcc -Wall -g -O2 -I/usr/local/include -m64 -o magent magent.o ketama.o /usr/lib64/libevent.a /usr/lib64/libm.a
/usr/lib64/libevent.a(event.o): In function `gettime':
/home/shuzhi/libevent-1.4.5-stable/event.c:150: undefined reference to `clock_gettime'
/usr/lib64/libevent.a(event.o): In function `detect_monotonic':
/home/shuzhi/libevent-1.4.5-stable/event.c:133: undefined reference to `clock_gettime'
解决办法：
gcc -lrt -Wall -g -O2 -I/usr/local/include -m64 -o magent magent.o ketama.o /usr/lib64/libevent.a /usr/lib64/libm.a
实例：
/opt/lnmp/memcached/bin/memcached -m 32m -d -l 192.168.4.222 -p 11211 -u root -P /opt/lnmp/memcached/memcached_11211.pid -c 256
/opt/lnmp/memcached/bin/memcached -m 32m -d -l 192.168.4.222 -p 11212 -u root -P /opt/lnmp/memcached/memcached_11212.pid -c 256
/opt/lnmp/memcached/bin/memcached -m 32m -d -l 192.168.4.222 -p 11213 -u root -P /opt/lnmp/memcached/memcached_11213.pid -c 256
magent -u root -n 51200 -l 127.0.0.1 -p 12000 -s 192.168.4.222:11211 -s 192.168.4.222:11212 -b 192.168.4.222:11213
注：
1、分别在11211、11212、11213端口启动3个Memcached进程，在12000端口开启magent代理程序；
2、11211、11212端口为主Memcached，11213端口为备份Memcached；
3、连接上12000的magent，set key1和set key2，根据哈希算法，key1被写入11212和11213端口的Memcached，key2被写入11212和11213端口的Memcached；
4、当11211、11212端口的Memcached死掉，连接到12000端口的magent取数据，数据会从11213端口的Memcached取出；
5、当11211、11212端口的Memcached重启复活，连接到12000端口，magent会从11211或11212端口的 Memcached取数据，由于这两台Memcached重启后无数据，因此magent取得的将是空值，尽管11213端口的Memcached还有数 据（此问题尚待改进）。
测试：
# telnet 127.0.0.1 12000
Trying 127.0.0.1...
Connected to Monitor (127.0.0.1).
Escape character is '^]'.
stats
memcached agent v0.6
matrix 1 -> 192.168.4.222:11211, pool size 0
matrix 2 -> 192.168.4.222:11212, pool size 0
END
set key1 0 0 9
chinatree
STORED
set key2 0 0 9
chinatree
STORED
quit
Connection closed by foreign host.
# telnet 192.168.4.222 11211
Trying 192.168.4.222...
Connected to 192.168.4.222.
Escape character is '^]'.
get key1
VALUE key1 0 9
chinatree
END
get key2
END
quit
Connection closed by foreign host.
# telnet 192.168.4.222 11212
Trying 192.168.4.222...
Connected to 192.168.4.222.
Escape character is '^]'.
get key1
END
get key2
VALUE key2 0 9
chinatree
END
quit
Connection closed by foreign host.
# telnet 192.168.4.222 11213
Trying 192.168.4.222...
Connected to 192.168.4.222.
Escape character is '^]'.
get key1
VALUE key1 0 9
chinatree
END
get key2
VALUE key2 0 9
chinatree
END
quit
Connection closed by foreign host.
模拟11211和11212端口全down掉
kill `cat /opt/lnmp/memcached/memcached_11211.pid` `cat /opt/lnmp/memcached/memcached_11212.pid`
# telnet 127.0.0.1 12000
Trying 127.0.0.1...
Connected to Monitor (127.0.0.1).
Escape character is '^]'.
get key1
VALUE key1 0 9
chinatree
END
get key2
VALUE key2 0 9
chinatree
END
quit
Connection closed by foreign host.
恢复11211和11212端口：
/opt/lnmp/memcached/bin/memcached -m 32m -d -l 192.168.4.222 -p 11211 -u root -P /opt/lnmp/memcached/memcached_11211.pid -c 256
/opt/lnmp/memcached/bin/memcached -m 32m -d -l 192.168.4.222 -p 11212 -u root -P /opt/lnmp/memcached/memcached_11212.pid -c 256
# telnet 127.0.0.1 12000
Trying 127.0.0.1...
Connected to Monitor (127.0.0.1).
Escape character is '^]'.
get key1
END
get key2
END
quit
Connection closed by foreign host.
参考网址：
https://code.google.com/p/memagent/
http://simblog.vicp.net/?p=105