1. 使用repcached
这个不做多的说明。
该方案优点：两个Memcached都可以进行读写操作，互相冗余。缺点：只支持单对单（一个master和一个slave），怎么样在多个memcached中使用repcached，我没找到答案。
2. 使用MAgent
项目地址：http://code.google.com/p/memagent/wiki/HowMagentWorks
安装：
mkdir magent cd magent wget http://memagent.googlecode.com/files/magent-0.5.tar.gz tar -xzvf magent-0.5.tar.gz /sbin/ldconfig sed -i "s#LIBS = -levent#LIBS = -levent -lm#g" Makefile make
分别在11211,11212,11213,11214端口启动4个memcached:
/usr/local/memcached/bin/memcached -d -p 11211 -u memcached -m 2048 -l 127.0.0.1 -p 11211 -c 300 -P/usr/local/memcached/memcached1.pid /usr/local/memcached/bin/memcached -d -p 11212 -u memcached -m 2048 -l 127.0.0.1 -p 11212 -c 300 -P/usr/local/memcached/memcached2.pid /usr/local/memcached/bin/memcached -d -p 11213 -u memcached -m 2048 -l 127.0.0.1 -p 11213 -c 300 -P/usr/local/memcached/memcached3.pid /usr/local/memcached/bin/memcached -d -p 11214 -u memcached -m 2048 -l 127.0.0.1 -p 11214 -c 300 -P/usr/local/memcached/memcached4.pid
[root@hd026-test agent]# ps aux | grep mem 533 4097 0.0 0.0 196688 2224 ? Ssl 14:47 0:00 /usr/local/memcached/bin/memcached -d -p 11211 -u memcached -m 2048 -l 127.0.0.1 -p 11211 -c 300 -P/usr/local/memcached/memcached1.pid 533 4105 0.0 0.0 131304 2224 ? Ssl 14:47 0:00 /usr/local/memcached/bin/memcached -d -p 11212 -u memcached -m 2048 -l 127.0.0.1 -p 11212 -c 300 -P/usr/local/memcached/memcached2.pid 533 4112 0.0 0.0 65768 2216 ? Ssl 14:47 0:00 /usr/local/memcached/bin/memcached -d -p 11213 -u memcached -m 2048 -l 127.0.0.1 -p 11213 -c 300 -P/usr/local/memcached/memcached3.pid 533 4123 0.0 0.0 131304 2212 ? Ssl 14:47 0:00 /usr/local/memcached/bin/memcached -d -p 11214 -u memcached -m 2048 -l 127.0.0.1 -p 11214 -c 300 -P/usr/local/memcached/memcached4.pid root 4248 0.0 0.0 61136 736 pts/0 S+ 15:07 0:00 grep mem
分别在12000,12001端口启动两个MAgent:
./magent -u root -n 4000 -l 127.0.0.1 -p 12000 -s 127.0.0.1:11211 -s 127.0.0.1:11212 -b 127.0.0.1:11213 -b 127.0.0.1:11214 ./magent -u root -n 4000 -l 127.0.0.1 -p 12001 -s 127.0.0.1:11211 -s 127.0.0.1:11212 -b 127.0.0.1:11213 -b 127.0.0.1:11214
启动参数说明：-p表示运行的端口号，-s表示指定那个memcached作为主，-b表示指定备份memcached；
[root@hd026-test agent]# ps aux | grep magent root 4139 0.0 0.0 17048 520 ? Ss 14:48 0:00 ./magent -u root -n 4000 -l 127.0.0.1 -p 12000 -s 127.0.0.1:11211 -s 127.0.0.1:11212 -b 127.0.0.1:11213 -b 127.0.0.1:11214 root 4169 0.0 0.0 17048 520 ? Ss 14:52 0:00 ./magent -u root -n 4000 -l 127.0.0.1 -p 12001 -s 127.0.0.1:11211 -s 127.0.0.1:11212 -b 127.0.0.1:11213 -b 127.0.0.1:11214 root 4288 0.0 0.0 61136 740 pts/0 S+ 15:11 0:00 grep magent
连接到MAgent-12000，插入key1:
[root@hd026-test agent]# telnet localhost 12000 Trying 127.0.0.1... Connected to localhost.localdomain (127.0.0.1). Escape character is '^]'. set key1 0 0 5 11111 STORED get key1 VALUE key1 0 5 11111 END quit Connection closed by foreign host.
连接到MAgent-12001，插入key2;
之后，分别连接Memcached-11211,Memcached-11212,Memcached-11213,Memcached-11214来get key1和key2,
发现key1在11212和11214中，key2在11211和11213中。
结构如下：
用户在连接到MAgent写数据时，MAgent会根据一定的算法将数据写入一个主memcached和一个备memcached;
这样，在主memcached挂掉时候，MAgent会从备memcached中读取数据，对用户来说是透明的。
实验一下：
kill掉Mem-11211：
kill 4097 [root@hd026-test agent]# ps aux | grep mem 533 4105 0.0 0.0 131304 2224 ? Ssl 14:47 0:00 /usr/local/memcached/bin/memcached -d -p 11212 -u memcached -m 2048 -l 127.0.0.1 -p 11212 -c 300 -P/usr/local/memcached/memcached2.pid 533 4112 0.0 0.0 65768 2216 ? Ssl 14:47 0:00 /usr/local/memcached/bin/memcached -d -p 11213 -u memcached -m 2048 -l 127.0.0.1 -p 11213 -c 300 -P/usr/local/memcached/memcached3.pid 533 4123 0.0 0.0 131304 2212 ? Ssl 14:47 0:00 /usr/local/memcached/bin/memcached -d -p 11214 -u memcached -m 2048 -l 127.0.0.1 -p 11214 -c 300 -P/usr/local/memcached/memcached4.pid root 4265 0.0 0.0 61136 740 pts/0 S+ 15:09 0:00 grep mem
在连接到MAgent-12000或者MAgent-12001, get key2:
[root@hd026-test agent]# telnet localhost 12000 Trying 127.0.0.1... Connected to localhost.localdomain (127.0.0.1). Escape character is '^]'. get key2 VALUE key2 0 5 22222 END get key1 VALUE key1 0 5 11111 END quit Connection closed by foreign host. [root@hd026-test agent]# telnet localhost 12001 Trying 127.0.0.1... Connected to localhost.localdomain (127.0.0.1). Escape character is '^]'. get key2 VALUE key2 0 5 22222 END get key1 VALUE key1 0 5 11111 END quit Connection closed by foreign host.
数据仍然可以正常获取。
使用该方案的优点是可以有多个memcached主从节点。
缺点是当一个主节点挂掉又恢复时候，从MAgent便会取不到数据。
测试如下：
重启11211端口的memcached
[root@hd026-test agent]# ps aux | grep mem 533 4105 0.0 0.0 131304 2224 ? Ssl 14:47 0:00 /usr/local/memcached/bin/memcached -d -p 11212 -u memcached -m 2048 -l 127.0.0.1 -p 11212 -c 300 -P/usr/local/memcached/memcached2.pid 533 4112 0.0 0.0 65768 2216 ? Ssl 14:47 0:00 /usr/local/memcached/bin/memcached -d -p 11213 -u memcached -m 2048 -l 127.0.0.1 -p 11213 -c 300 -P/usr/local/memcached/memcached3.pid 533 4123 0.0 0.0 131304 2212 ? Ssl 14:47 0:00 /usr/local/memcached/bin/memcached -d -p 11214 -u memcached -m 2048 -l 127.0.0.1 -p 11214 -c 300 -P/usr/local/memcached/memcached4.pid 533 4270 0.0 0.0 130280 1144 ? Ssl 15:09 0:00 /usr/local/memcached/bin/memcached -d -p 11211 -u memcached -m 2048 -l 127.0.0.1 -p 11211 -c 300 -P/usr/local/memcached/memcached1.pid root 4279 0.0 0.0 61136 740 pts/0 S+ 15:10 0:00 grep mem
[root@hd026-test agent]# telnet localhost 12000 Trying 127.0.0.1... Connected to localhost.localdomain (127.0.0.1). Escape character is '^]'. get key2 END get key1 VALUE key1 0 5 11111 END quit Connection closed by foreign host.
get key2,发现已经取不到数据，但其实key2在Mem-11213上还是存在的。
[root@hd026-test agent]# telnet localhost 11213 Trying 127.0.0.1... Connected to localhost.localdomain (127.0.0.1). Escape character is '^]'. get key2 VALUE key2 0 5 22222 END quit Connection closed by foreign host.
这其实是个很致命的缺陷，不知道为何没人修复。。或许有其他的方案可以弥补。。