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memcached是针对数据库的缓存软件 能有效降低数据库的负载
下面是何如将多个memcached做成集群负载均衡,让memcached变的更高可用一、安装步骤：
1、编译安装libevent：2、编译安装Memcached：
3、编译安装magent：
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二、实例：
1、分别在10.1.94.100 – 10.1.94.102 3台机器的11211端口启动3个Memcached进程，在12000端口开启magent代理程序；(以此类推可在不同机器上启动memcached)
2、10.1.94.100和101为主Memcached，10.1.94.102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10.1.94.100和10.1.94.102的Memcached，key2被写入
10.1.94.101和10.1.94.102的Memcached；4、当10.1.94.100和101的Memcached死掉，连接到12000端口的magent取数据，数据会从10.1.94.102的Memcached取出；
5、当10.1.94.100和101的Memcached重启复活，连接到12000端口，magent会从10.1.94.100或10.1.94.101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10.1.94.102的Memcached还有数据(此问题尚待改进)。
三、整个测试流程：
先在magent中添加1个key 如下:
telnet 127.0.0.1 12000
Trying 127.0.0.1… Connected to 127.0.0.1. Escape character is ‘^]’. stats memcached agent v0.4 matrix 1 -> 127.0.0.1:11211, pool size 0 matrix 2 -> 127.0.0.1:11212, pool size 0 END set key1 0 0 8 wangqi STORED set key2 0 0 8 wangqi STORED quit Connection closed by foreign host.然后在2个轮询的memcached中get刚才添加的key是否返回正确:
telnet 10.1.94.100 11211
Trying 10.1.94.100… Connected to 10.1.94.100. Escape character is ‘^]’. get key1 END get key2 VALUE key2 0 8 wangqi END quit Connection closed by foreign host. telnet 10.1.94.101 11211 Trying 10.1.94.101… Connected to 10.1.94.101. Escape character is ‘^]’. get key1 VALUE key1 0 8 wangqi END get key2 END quit Connection closed by foreign host. telnet 10.1.94.103 11211 Trying 10.1.94.103… Connected to 10.1.94.103. Escape character is ‘^]’. get key1 VALUE key1 0 8 wangqi END get key2 VALUE key2 0 8 wangqi END quit Connection closed by foreign host. 模拟10.1.94.100和101的Memcached死掉 直接kill进程然后:telnet 127.0.0.1 12000
Trying 127.0.0.1… Connected to 127.0.0.1. Escape character is ‘^]’. get key1 VALUE key1 0 8 wangqi END get key2 VALUE key2 0 8 wangqi END quit Connection closed by foreign host. 模拟10.1.94.100和101的Memcached重启复活 telnet 127.0.0.1 12000 Trying 127.0.0.1… Connected to 127.0.0.1. Escape character is ‘^]’. get key1 END get key2 END quit Connection closed by foreign host. magent -u root(启动用户uid) -n 51200(最大连接数) -l 127.0.0.1(ip地址) -p 12000(监听端口) -s 127.0.0.1:11211(memcached的ip) -s 127.0.0.1:11212(memcached的ip) -b 127.0.0.1:11213(备份memcached的ip)如果不需要轮询hash的话 只有一主一备就可以了 但是在主当掉后备份memcached接手 然后在主服务恢复后数据会根据主服务器走….
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