MemCached入門

1.MemCached是什麼？

MemCached是一個開源的高性能的分佈式內存對象緩存系統，在Web應用中用於減輕數據庫負載。我們可以將使用頻率較高，且要求時效性不嚴格的數據緩存到MemCached中，以減少讀取數據庫的次數，從而減低數據庫壓力。

2.MemCached在網站架構中的位置？

3.MemCached特點:

MemCached作爲高速運行的分佈式緩存服務器，具有以下的特點。

· 協議簡單

· 基於libevent的事件處理

· 內置內存存儲方式

· MemCached不互相通信的分佈式

4.MemCached的運行圖：

5.MemCached的數據過期方式：

6.MemCached的安裝：

在windows下的安裝：

下載Windows平臺下的MemCached，地址爲：http://code.jellycan.com/files/memcached-1.2.6-win32-bin.zip

對應的源代碼地址爲：http://code.jellycan.com/files/memcached-1.2.6-win32-src.zip

然後，解壓開來，會看到一個memcached.exe文件，進行如下圖的安裝，將以系統服務的形式安裝到機上

然後查看系統服務，會發現已經可以看到memcached服務了

然後，選中此服務點鼠標右鍵，啓動此服務。

在DOS界面中輸入：telnet 127.0.0.1 11211來確認服務是否啓動無誤，如果無誤，則會顯示如下窗口：

上面圖中顯示的ERROR是我隨便輸入字符後按回車顯示的，這是因爲你需要安裝memcached規定的協議來進行輸入，否則就顯示如上所示錯誤。

在linux下的安裝：

安裝libevent庫

cd /usr/local/src
wget http://monkey.org/~provos/libevent-1.3b.tar.gz
tar zxvf libevent-1.3b.tar.gz
cd libevent-1.3b
./configure
make && make install

安裝成功
安裝memcache

cd /usr/local/src
wget http://danga.com/memcached/dist/memcached-1.2.5.tar.gz
tar zxvf memcached-1.2.5.tar.gz
cd memcached-1.2.5
./configure
make && make install

啓動

cd  usr/local/bin
bin] # memcached –h
出錯
memcached: error while loading shared libraries: libevent-1.3b.so.1: cannot open shared object file: No such file or directory

google解決方法: http://bbs.yiwz.net/archiver/?tid-86.html

則運行 LD_DUBUG=libs 就可以知道memcached啓動時庫的加載路徑。具體如下

[root@bogon  usr/local/bin]# LD_DEBUG=libs  memcached –v
      5112:     find library=libevent-1.3b.so.1 [0]; searching
      5112:      search cache=/etc/ld.so.cache
      5112:      search path=/lib/tls/i686/sse2:/lib/tls/i686:/lib/tls/sse2:/lib/tls:/lib/i686/sse2:/lib/i686:/lib/sse2:/lib:/usr/lib/tls/i686/sse2:/usr/lib/tls/i686:/usr/lib/tls/sse2:/usr/lib/tls:/usr/lib/i686/sse2:/usr/lib/i686:/usr/lib/sse2:/usr/lib           (system search path)
      5112:       trying file=/lib/tls/i686/sse2/libevent-1.3b.so.1
      5112:       trying file=/lib/tls/i686/libevent-1.3b.so.1
      5112:       trying file=/lib/tls/sse2/libevent-1.3b.so.1
      5112:       trying file=/lib/tls/libevent-1.3b.so.1
      5112:       trying file=/lib/i686/sse2/libevent-1.3b.so.1
      5112:       trying file=/lib/i686/libevent-1.3b.so.1
      5112:       trying file=/lib/sse2/libevent-1.3b.so.1
      5112:       trying file=/lib/libevent-1.3b.so.1
      5112:       trying file=/usr/lib/tls/i686/sse2/libevent-1.3b.so.1
      5112:       trying file=/usr/lib/tls/i686/libevent-1.3b.so.1
      5112:       trying file=/usr/lib/tls/sse2/libevent-1.3b.so.1
      5112:       trying file=/usr/lib/tls/libevent-1.3b.so.1
      5112:       trying file=/usr/lib/i686/sse2/libevent-1.3b.so.1
      5112:       trying file=/usr/lib/i686/libevent-1.3b.so.1
      5112:       trying file=/usr/lib/sse2/libevent-1.3b.so.1
      5112:       trying file=/usr/lib/libevent-1.3b.so.1

然後給libevent-1.3b.so.1建立一個鏈接：

[root@bogon ~]# sudo ln -s /usr/local/lib/libevent-1.3b.so.1 /lib/libevent-1.3b.so.1

檢查是否建立成功

[root@bogon ~]# ls -al /lib|grep libevent
lrwxrwxrwx  1 root root      33 Aug 25 19:52 libevent-1.3b.so.1 -> /usr/local/lib/libevent-1.3b.so.1

此時在

bin] # memcached –h

memcached 1.2.5
-p <num>      TCP port number to listen on (default: 11211)
-U <num>      UDP port number to listen on (default: 0, 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 is INDRR_ANY
-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 is 64 MB
-M            return error on memory exhausted (rather than removing items)
-c <num>      max simultaneous connections, default is 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)
-h            print this help and exit
-i            print memcached and libevent license
-b            run a managed instanced (mnemonic: buckets)
-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

現在MemCache成功搞定

默認情況下memcached安裝到/usr/local/bin下。

啓動：

[root@bogon bin]# memcached -d -m 128 -u root -p 11211

檢查是否已經啓動

[root@bogon bin]#  telnet 127.0.0.1 11211
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.

這裏使用的memcached啓動選項的內容如下。
選項說明
p 使用的TCP端口。默認爲11211
m 最大內存大小。默認爲64M
vv 用very vrebose模式啓動，調試信息和錯誤輸出到控制檯
d 作爲daemon在後臺啓動

查看MemCached的內部狀態

[root@bogon bin]# cd /usr/local/bin
[root@bogon bin]# telnet 127.0.0.1 11211
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
stats
STAT pid 6779
STAT uptime 14217
STAT time 1314343512
STAT version 1.2.5
STAT pointer_size 32
STAT rusage_user 0.002999
STAT rusage_system 0.027995
STAT curr_items 0
STAT total_items 0
STAT bytes 0
STAT curr_connections 3
STAT total_connections 4
STAT connection_structures 4
STAT cmd_get 0
STAT cmd_set 0
STAT get_hits 0
STAT get_misses 0
STAT evictions 0
STAT bytes_read 56
STAT bytes_written 482
STAT limit_maxbytes 134217728
STAT threads 1
END
Quit

到此爲止說明你的MemCached安裝成功了