Memcached学习——（一）

原文地址： http://snowolf.iteye.com/blog/1447348

 

08年的时候接触过Memcached，当时还对它的客户端产品嗤之以鼻，毕竟手工代码没有各种ORM原生XML配置方便。尽管如此，Memcached现在已经成了服务器架构里不可或缺的一部分！ 

相关链接： 
Memcached笔记——（一）安装&常规错误&监控 
Memcached笔记——（二）XMemcached&Spring集成 
Memcached笔记——（三）Memcached使用总结 
Memcached笔记——（四）应对高并发攻击 


一、下载 
1.Libevent 
简单的说就是一个事件触发的网络库，Memcached离不开它。 

wget http://cloud.github.com/downloads/libevent/libevent/libevent-2.0.17-stable.tar.gz

2.Memcached 
今天的主角 

wget http://memcached.googlecode.com/files/memcached-1.4.13.tar.gz

二、安装 
1.Libevent 
解压缩 

tar zxvf libevent-2.0.17-stable.tar.gz

编译、安装 

./configure --prefix=/usr && make && make install

这里一定要注意指定--prefix，后面配置memcached的时候就有必要用到。 
2.Memcached 
解压 

tar zxvf memcached-1.4.13.tar.gz

编译、安装 

./configure --with-libevent=/usr/lib && make && make install

这里一定要指定libevent的路径，否则启动的时候就有找不到libevent的so文件的错误！ 
启动 

memcached -d -m 512 -p 11211 -u root -c 256 -P /var/run/memcached.pid

参数 

引用

-p <num>      TCP port number to listen on (default: 11211) 
-U <num>      UDP port number to listen on (default: 11211, 0 is off) 
-l <addr>     interface to listen on (default: INADDR_ANY, all addresses) 
              <addr> may be specified as host:port. If you don't specify 
              a port number, the value you specified with -p or -U is 
              used. You may specify multiple addresses separated by comma 
              or by using -l multiple times 
-d            run as a daemon 
-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) 
-v            verbose (print errors/warnings while in event loop) 
-P <file>     save PID in <file>, only used with -d option 

要关掉memcached 

kill -9 `cat /var/run/memcached.pid`

是否正常？Telnet上去看看 

telnet xxx.xxx.xxx.xxx 11211

然后输入

stats

接着就能看到： 

引用

STAT pid 3021 
STAT uptime 3621 
STAT time 1331261509 
STAT version 1.4.13 
STAT libevent 2.0.17-stable 
STAT pointer_size 64 
STAT rusage_user 0.000000 
STAT rusage_system 0.000999 
STAT curr_connections 6 
STAT total_connections 7 
STAT connection_structures 7 
STAT reserved_fds 20 
STAT cmd_get 0 
STAT cmd_set 0 
STAT cmd_flush 0 
STAT cmd_touch 0 
STAT get_hits 0 
STAT get_misses 0 
STAT delete_misses 0 
STAT delete_hits 0 
STAT incr_misses 0 
STAT incr_hits 0 
STAT decr_misses 0 
STAT decr_hits 0 
STAT cas_misses 0 
STAT cas_hits 0 
STAT cas_badval 0 
STAT touch_hits 0 
STAT touch_misses 0 
STAT auth_cmds 0 
STAT auth_errors 0 
STAT bytes_read 72 
STAT bytes_written 1038 
STAT limit_maxbytes 52428800 
STAT accepting_conns 1 
STAT listen_disabled_num 0 
STAT threads 4 
STAT conn_yields 0 
STAT hash_power_level 16 
STAT hash_bytes 524288 
STAT hash_is_expanding 0 
STAT expired_unfetched 0 
STAT evicted_unfetched 0 
STAT bytes 0 
STAT curr_items 0 
STAT total_items 0 
STAT evictions 0 
STAT reclaimed 0 
END 

上面状况说明Memcached服务正常。 
还可以试试get、set、delete、replace 

引用

set foo 0 0 3     （保存命令） 
bar               （数据） 
STORED            （结果） 
get foo           （取得命令） 
VALUE foo 0 3     （数据） 
bar               （数据）

输入

quit

退出。 

三、系统服务 
参照Nginx的系统服务，自己写了一个Memcached的系统服务脚本。 
先构建/etc/init.d/memcahed这个文件，然后赋予其可执行权限： 

touch /etc/init.d/memcached
chmod +x /etc/init.d/memcached

memcached脚本如下： 

#!/bin/bash
# v.0.0.1
# create by snowolf at 2012.5.25
#
# memcached  - This shell script takes care of starting and stopping memcached.
#
# chkconfig: - 90 10
# description: Memcache provides fast memory based storage.
# processname: memcached

memcached_path="/usr/local/bin/memcached"
memcached_pid="/var/run/memcached.pid"
memcached_memory="1024"

# Source function library.
. /etc/rc.d/init.d/functions

[ -x $memcached_path ] || exit 0

RETVAL=0
prog="memcached"

# Start daemons.
start() {
    if [ -e $memcached_pid -a ! -z $memcached_pid ];then
        echo $prog" already running...."
        exit 1
    fi

    echo -n $"Starting $prog "
    # Single instance for all caches
    $memcached_path -m $memcached_memory -l 0.0.0.0 -p 11211 -u root -d -P $memcached_pid
    RETVAL=$?
    [ $RETVAL -eq 0 ] && {
        touch /var/lock/subsys/$prog
        success $"$prog"
    }
    echo
    return $RETVAL
}


# Stop daemons.
stop() {
    echo -n $"Stopping $prog "
    killproc -d 10 $memcached_path
    echo
    [ $RETVAL = 0 ] && rm -f $memcached_pid /var/lock/subsys/$prog

    RETVAL=$?
    return $RETVAL
}

# See how we were called.
case "$1" in
        start)
            start
            ;;
        stop)
            stop
            ;;
        status)
            status $prog
            RETVAL=$?
            ;;
        restart)
            stop
            start
            ;;
        *)
            echo $"Usage: $0 {start|stop|status|restart}"
            exit 1
esac
exit $RETVAL

注意这几行配置，请根据实际情况配置memcached执行文件路径，以及Memcached使用内存大小： 

引用

memcached_path="/usr/local/bin/memcached" 
memcached_memory="1024"

追加为系统服务： 

chkconfig --add memcached
chkconfig memcached on

然后就可以通过service memcached start|stop|status|restart控制memcached了！ 

四、常规错误 
一开始没有指定libevent路径安装memcached的时候，启动memcached就报这个错误： 

引用

memcached: error while loading shared libraries: libevent-2.0.so.5: cannot open shared object file: No such file or directory 

其实这个文件就在/usr/lib下。错就错在Linux是64bit系统，如果没有指定libevent路径，memcached就会去/usr/lib64下去找。 
找到这个文件 

whereis libevent-2.0.so.5

引用

libevent-2.0.so: /usr/lib/libevent-2.0.so.5

ldd /usr/local/bin/memcached

提示找不到libevent-2.0.so.5 

引用

        linux-vdso.so.1 =>  (0x00007fff41dfd000) 
        libevent-2.0.so.5 => not found 
        librt.so.1 => /lib64/librt.so.1 (0x0000003c94a00000) 
        libpthread.so.0 => /lib64/libpthread.so.0 (0x0000003c93a00000) 
        libc.so.6 => /lib64/libc.so.6 (0x0000003c92e00000) 
        /lib64/ld-linux-x86-64.so.2 (0x0000003c92a00000)

定位 

LD_DEBUG=libs /usr/local/bin/memcached -v

引用

     19905:     find library=libevent-2.0.so.5 [0]; searching 
     19905:      search path=/usr/lib/lib/tls/x86_64:/usr/lib/lib/tls:/usr/lib/lib/x86_64:/usr/lib/lib          (RPATH from file /usr/local/bin/memcached) 
     19905:       trying file=/usr/lib/lib/tls/x86_64/libevent-2.0.so.5 
     19905:       trying file=/usr/lib/lib/tls/libevent-2.0.so.5 
     19905:       trying file=/usr/lib/lib/x86_64/libevent-2.0.so.5 
     19905:       trying file=/usr/lib/lib/libevent-2.0.so.5 
     19905:      search cache=/etc/ld.so.cache 
     19905:      search path=/lib64/tls/x86_64:/lib64/tls:/lib64/x86_64:/lib64:/usr/lib64/tls/x86_64:/usr/lib64/tls:/usr/lib64/x86_64:/usr/lib64            (system search path) 
     19905:       trying file=/lib64/tls/x86_64/libevent-2.0.so.5 
     19905:       trying file=/lib64/tls/libevent-2.0.so.5 
     19905:       trying file=/lib64/x86_64/libevent-2.0.so.5 
     19905:       trying file=/lib64/libevent-2.0.so.5 
     19905:       trying file=/usr/lib64/tls/x86_64/libevent-2.0.so.5 
     19905:       trying file=/usr/lib64/tls/libevent-2.0.so.5 
     19905:       trying file=/usr/lib64/x86_64/libevent-2.0.so.5 
     19905:       trying file=/usr/lib64/libevent-2.0.so.5 
     19905: 
/usr/local/bin/memcached: error while loading shared libraries: libevent-2.0.so.5: cannot open shared object file: No such file or directory 

注意这句： 

引用

19905: trying file=/usr/lib64/libevent-2.0.so.5

做个软连接 

ln -s /usr/lib/libevent-2.0.so.5 /usr/lib64/libevent-2.0.so.5

再试试： 

ldd /usr/local/bin/memcached

这回找到了！ 

引用

        linux-vdso.so.1 =>  (0x00007fffffef6000) 
        libevent-2.0.so.5 => /usr/lib64/libevent-2.0.so.5 (0x00002b5608a26000) 
        librt.so.1 => /lib64/librt.so.1 (0x0000003c94a00000) 
        libpthread.so.0 => /lib64/libpthread.so.0 (0x0000003c93a00000) 
        libc.so.6 => /lib64/libc.so.6 (0x0000003c92e00000) 
        /lib64/ld-linux-x86-64.so.2 (0x0000003c92a00000)

五、监控 
可以在服务器上配置一个PHP页面来监测Memcached的情况， 
下载MemcachePHP 



配置也比较简单，主要包括账户配置，以及Memcached Server地址配置。 

define('ADMIN_USERNAME','memcache');    // Admin Username
define('ADMIN_PASSWORD','password');    // Admin Password
define('DATE_FORMAT','Y/m/d H:i:s');
define('GRAPH_SIZE',200);
define('MAX_ITEM_DUMP',50);

$MEMCACHE_SERVERS[] = 'mymemcache-server1:11211'; // add more as an array
$MEMCACHE_SERVERS[] = 'mymemcache-server2:11211'; // add more as an array

如果不方便搭建PHP服务，可以使用Perl脚本memcache-top 
修改@default_instances或使用--instances参数： 

perl memcache-top-v0.6 --instances 10.11.155.26 10.11.155.41

 

先到这里，后续做压力测试，Java客户端开发，Spring系统集成等。