memcached服务

如果实际生产环境中，缓存服务器需要重启（或者断电），那么缓存中的数据将会丢失，那么这时后端的服务器
并发压力会增大，可能会导致后端的服务器也跟着宕机，无法提供服务，
那么这时我们的处理流程是这样的：
首先从负载均衡中将 WEB 应用停掉----->让负载均衡不再转发数据给 WEB---->接着启动缓存服务器-------->
通过程序把数据库的内容初始化到缓存服务器中------->然后将 web 应用启用------->重启数据库服务器

1、设置缓存（expires）和 deflate 压缩，可以将一些内容直接缓存在用户端的本地，下次访问直接调用本地
2、 CDN 缓存静态内容（html、图片等），当用户请求这些内容时直接调用 CDN 的内容，不再请求后端服务器了
3、 Apache 和 Nginx 静态服务器提供静态内容（通过异步消息队列生成静态内容）
4、 PHP 和 JAVA 动态内容
5、数据库的 memcached 缓存服务器
6、数据库服务器（MYSQL）
7、数据库的存储服务器

[root@cairui ~]# cat /etc/redhat-release 
CentOS release 6.8 (Final)
[root@cairui ~]# uname -r
2.6.32-696.6.3.el6.x86_64

[root@cairui software]# tar xf libevent-2.1.8-stable.tar.gz 
[root@cairui software]# cd libevent-2.1.8-stable
[root@cairui libevent-2.1.8-stable]# ./configure 
[root@cairui libevent-2.1.8-stable]# make
[root@cairui libevent-2.1.8-stable]# make install

[root@cairui libevent-2.1.8-stable]# yum install memcached
[root@cairui libevent-2.1.8-stable]# find / -name memcached
/etc/sysconfig/memcached
/etc/rc.d/init.d/memcached
/usr/bin/memcached
/var/run/memcached

[root@cairui lib]# echo "/usr/local/lib">>/etc/ld.so.conf
[root@cairui lib]# ldconfig 
[root@cairui lib]# which memcached
/usr/bin/memcached

[root@cairui lib]# /usr/bin/memcached -h
memcached 1.4.4
-p <num>      TCP port number to listen on (default: 11211)　　#指定监听端口
-U <num>      UDP port number to listen on (default: 11211, 0 is off)
-s <file>     UNIX socket path to listen on (disables network support)
-a <mask>     access mask for UNIX socket, in octal (default: 0700)
-l <ip_addr>  interface to listen on (default: INADDR_ANY, all addresses)　　#指定监听地址
-d            run as a daemon　　#后台模式启动
-r            maximize core file limit　　#最大的文件字符集
-u <username> assume identity of <username> (only when run as root)　　#指定用户
-m <num>      max memory to use for items in megabytes (default: 64 MB)　　#分配内存区大小
-M            return error on memory exhausted (rather than removing items)
-c <num>      max simultaneous connections (default: 1024)　　#最大并发数
-k            lock down all paged memory.  Note that there is a
              limit on how much memory you may lock.  Trying to
              allocate more than that would fail, so be sure you
              set the limit correctly for the user you started
              the daemon with (not for -u <username> user;
              under sh this is done with 'ulimit -S -l NUM_KB').
-v            verbose (print errors/warnings while in event loop)
-vv           very verbose (also print client commands/reponses)　　#以very verbose模式启动
-vvv          extremely verbose (also print internal state transitions)
-h            print this help and exit
-i            print memcached and libevent license
-P <file>     save PID in <file>, only used with -d option　　#设置保存memcached的PID
-f <factor>   chunk size growth factor (default: 1.25)
-n <bytes>    minimum space allocated for key+value+flags (default: 48)
-L            Try to use large memory pages (if available). Increasing
              the memory page size could reduce the number of TLB misses
              and improve the performance. In order to get large pages
              from the OS, memcached will allocate the total item-cache
              in one large chunk.
-D <char>     Use <char> as the delimiter between key prefixes and IDs.
              This is used for per-prefix stats reporting. The default is
              ":" (colon). If this option is specified, stats collection
              is turned on automatically; if not, then it may be turned on
              by sending the "stats detail on" command to the server.
-t <num>      number of threads to use (default: 4)
-R            Maximum number of requests per event, limits the number of
              requests process for a given connection to prevent 
              starvation (default: 20)
-C            Disable use of CAS
-b            Set the backlog queue limit (default: 1024)
-B            Binding protocol - one of ascii, binary, or auto (default)
-I            Override the size of each slab page. Adjusts max item size
              (default: 1mb, min: 1k, max: 128m)　　

[root@cairui lib]# memcached -p 11111 -u root -c 1024 -d
[root@cairui lib]# lsof -i:11111
COMMAND     PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
memcached 17416 root   26u  IPv4  90768      0t0  TCP *:vce (LISTEN)
memcached 17416 root   27u  IPv4  90785      0t0  UDP *:vce 
[root@cairui lib]# netstat -lntup|grep mem
tcp        0      0 0.0.0.0:11111               0.0.0.0:*                   LISTEN      17416/memcached     
udp        0      0 0.0.0.0:11111               0.0.0.0:*                               17416/memcached     

[root@cairui ~]# printf "set key001 0 0 10\r\ntest123456\r\n"|nc 127.0.0.1 11111　　#写入数据
STORED
[root@cairui ~]# printf "get key001\r\n"|nc 127.0.0.1 11111　　#查询数据
VALUE key001 0 10
test123456
END
[root@cairui ~]# printf "delete key001\r\n"|nc 127.0.0.1 11111　　#删除数据
DELETED
[root@cairui ~]# printf "get key001\r\n"|nc 127.0.0.1 11111
END

正确关闭 memcached 服务
一般启动时最好指定下 PID
[root@LVS-2 ~]# memcached -p 11213 -u root -m 16m -c 1024 -d -P /var/run/11213.pid #指定进程文件
[root@LVS-2 ~]# kill `cat /var/run/11213.pid`
提示：实际生产环境中，要布署 memcached 服务，做为数据缓存，内存的指定大小是根据业务来确定，是不是需要负载均衡？最好同开发一起讨论确定好，还有它还有分客户端与服务端
配置 session 会话共享存储
vi /applicaton/php/lib/php.ini
session.save_path = "/tmp"改成 memcached 服务器地址 tcp ://10.10.10.1:11211
session.save_handler = files（改成 memcached）
将所有的 WEB 服务器(WEB 服务器需要安装客户端)里的 PHP 配置文件改成上述配置，即可完成会话共享存储

[root@LB01 vhost]# cd /web/www/
[root@LB01 www]# wget http://www.junopen.com/memadmin/memadmin-1.0.12.tar.gz
[root@LB01 www]# tar zxf memadmin-1.0.12.tar.gz
无需安装，解压即可