memcached是一套分布式的高速缓存系统，由LiveJournal的Brad Fitzpatrick开发，但被许多网站使用。这是一套开放源代码软件，以BSD license授权发布。

memcached作为高速运行的分布式缓存服务器，具有以下的特点。
·基于c/s__架构，协议简单
·基于libevent__的事件处理
·内置内存存储方式（slab allowcation__）
· memcached不互相通信的分布式
· 数据过期方式：Lazy Expiration 和 LRU

Mencached的数据流向
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1.安装Memcached

安装必要memcached libmemcached libevent

  1. # yum install -y memcached libmemcached libevent

开启memcached服务

  1. # systemctl start memcached

2.查看memcached运行状态

  1. # memcached-tool 127.0.0.1:11211  stats 
  2. #echo stats |nc 127.0.0.1 11211    //需要安装nc工具  yum install -y nc
  3. #memstat --servers=127.0.0.1:11211  //安装memcached后可使用
  5. #127.0.0.1:11211   Field       Value
  6.          accepting_conns           1
  7.                auth_cmds           0
  8.              auth_errors           0
  9.                    bytes           0
  10.               bytes_read         196
  11.            bytes_written        1172
  12.               cas_badval           0
  13.                 cas_hits           0
  14.               cas_misses           0
  15.                cmd_flush           0
  16.                  cmd_get           5
  17.                  cmd_set           3
  18.                cmd_touch           0
  19.              conn_yields           0
  20.    connection_structures          11
  21.         curr_connections          10
  22.               curr_items           0
  23.                decr_hits           0
  24.              decr_misses           0
  25.              delete_hits           1
  26.            delete_misses           0
  27.        evicted_unfetched           0
  28.                evictions           0
  29.        expired_unfetched           0
  30.                 get_hits           3
  31.               get_misses           2
  32.               hash_bytes      524288
  33.        hash_is_expanding           0
  34.         hash_power_level          16
  35.                incr_hits           0
  36.              incr_misses           0
  37.                 libevent 2.0.21-stable
  38.           limit_maxbytes    67108864
  39.      listen_disabled_num           0
  40.                      pid        2319
  41.             pointer_size          64
  42.                reclaimed           1
  43.             reserved_fds          20
  44.            rusage_system    0.041016
  45.              rusage_user    0.000131
  46.                  threads           4
  47.                     time  1646617228
  48.        total_connections          16
  49.              total_items           3
  50.               touch_hits           0
  51.             touch_misses           0
  52.                   uptime         793
  53.                  version      1.4.15

3.Memcached命令行

  1. # yum install -y telnet nc
  2. # telnet 127.0.0.1 11211
  3. Trying 127.0.0.1...
  4. Connected to 127.0.0.1.
  5. Escape character is '^]'.
  6. set key2 0 30 2
  7. ab
  8. STORED
  9. get key2
  10. VALUE key2 0 2
  11. ab
  12. END

4.Mencached数据示例

  1. # telnet 127.0.0.1 11211
  2. Trying 127.0.0.1...
  3. Connected to 127.0.0.1.
  4. Escape character is '^]'.
  5. set key3 1 100 4
  6. abcd
  7. STORED
  8. get key3
  9. VALUE key3 1 4
  10. abcd
  11. END
  13. replace key3 1 200 5
  14. abcdx
  15. STORED
  17. get key3
  18. VALUE key3 1 5
  19. abcdx
  20. END
  22. delete key3
  23. DELETED
  25. get key3
  26. END

5.Memcached数据导出和导入

  1. # memcached-tool 127.0.0.1:11211 dump > data.txt
  2. Dumping memcache contents
  3.   Number of buckets: 0
  4.   Number of items  : 
  5. nc 127.0.0.1 11211 < data.txt