CentOS 5.2下Memcache的安装与配置

一，memcache简单介绍：

memcached是高性能的分布式内存缓存服务器，为了提高性能，memcached中的数据都保存在内存中，重启memcached及重启操作系统都会导致缓存中的数据全部丢失，其缓存的数据达到指定的内存分配值之后，就会使用LRU算法删除不使用的缓存。（LRU算法的基本概念：当分配的内存可用空间不足时，它尽可能地先保留最常用的数据，将最近没有使用的数据移出内存，释放出的空间来存储其它的数据。）

其作用是缓存数据库查询结果，这样就减少了对数据库的访问次数据，从而减轻数据库的压力，这样就提高了用户的访问速度，典型应用如下图所示：

二，安装服务器端：

1，安装libevent库，它将Linux的epoll、freebsd操作系统的kqueue等事件处理功能封装成统一的接口，memcached使用这个库，可以发挥其高性能。

[root@youxia205 opt]# yum install libevent libevent-devel

2，下载memcache源码包：

[root@youxia205 opt]# wget http://memcached.googlecode.com/files/memcached-1.4.5.tar.gz

3，解压、编译、安装：

[root@youxia205 opt]# tar -zxvf memcached-1.4.5.tar.gz

[root@youxia205 opt]# cd memcached-1.4.5

[root@youxia205 memcached-1.4.5]# ./configure

[root@youxia205 memcached-1.4.5]# make && make install

4，安装完成之后可以看下memcache的参数：

[root@youxia205 local]# memcached -help

memcached 1.4.5

-p <num>      TCP port number to listen on (default: 11211)

-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)

-d            run as a daemon

-r            maximize core file limit

-u <username> assume identity of <username> (only when run as root)

-m <num>      max memory to use for items in megabytes (default: 64 MB)

-M            return error on memory exhausted (rather than removing items)

-c <num>      max simultaneous connections (default: 1024)

-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)

-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

-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)