Memcached笔记——（一）安装&常规错误&监控

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

常见错误：

引用

Warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/usr/local/apache.../memcache.php on line 726

在memcache.php顶端加上“date_default_timezone_set('Asia/Hong_Kong');”即可，具体地域设置参考： http://www.php.net/manual/zh/datetime.configuration.php#ini.date.timezone

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。

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