Linux下Memcached的安装、使用

Linux Distribution：Ubuntu 14

Libevent：1.4.14b

下载地址：libevent官网

Memcached：1.4.25

下载地址：memcached官网

一，安装memcached

Memcached的安装依赖Libevent，首先安装Libevent：

sean@sean:~$ tar -xzf libevent-1.4.14b-stable.tar.gz 
sean@sean:~$ cd libevent-1.4.14b-stable/
sean@sean:~/libevent-1.4.14b-stable$ sudo ./configure -prefix /usr
sean@sean:~/libevent-1.4.14b-stable$ sudo make
sean@sean:~/libevent-1.4.14b-stable$ sudo make install
sean@sean:~/libevent-1.4.14b-stable$ sudo make clean

Libevent将会被安装至/usr/lib下

sean@sean:/usr/lib$ cd /usr/lib/
sean@sean:/usr/lib$ ll | grep libevent*
Binary file libevent-1.4.so.2.2.0 matches
libevent.la:dlname='libevent-1.4.so.2'
libevent.la:library_names='libevent-1.4.so.2.2.0 libevent-1.4.so.2 libevent.so'
Binary file libevent.so matches

然后安装Memcached：

sean@sean:~$ tar -xzf memcached-1.4.25.tar.tar
sean@sean:~$ cd memcached-1.4.25/
sean@sean:~/memcached-1.4.25$ sudo ./configure -with-libevent=/usr
sean@sean:~/memcached-1.4.25$ sudo make
sean@sean:~/memcached-1.4.25$ sudo make install
sean@sean:~/memcached-1.4.25$ sudo make clean

Memcached将会被安装至/usr/local/bin下：

sean@sean:/usr/local/bin$ ll
total 544
drwxr-xr-x  2 root root   4096  4月 21 21:32 ./
drwxr-xr-x 10 root root   4096  2月 18 07:12 ../
-rwxr-xr-x  1 root root 545998  4月 21 21:32 memcached*

二，启动memcached服务

-m：分配给memcached的最大内存，以M为单位

-p：服务监听的TCP端口，默认值是11211

-d：服务当做守护进程启动

-vv：打印详细信息

-f：增长因子，默认值是1.25，指定的值必须比1大

sean@sean:/usr/local/bin$ ./memcached -m 64 -p 9999 -d -vv
sean@sean:/usr/local/bin$ slab class   1: chunk size        96 perslab   10922
slab class   2: chunk size       120 perslab    8738
slab class   3: chunk size       152 perslab    6898
slab class   4: chunk size       192 perslab    5461
slab class   5: chunk size       240 perslab    4369
slab class   6: chunk size       304 perslab    3449
slab class   7: chunk size       384 perslab    2730
slab class   8: chunk size       480 perslab    2184
slab class   9: chunk size       600 perslab    1747
slab class  10: chunk size       752 perslab    1394
slab class  11: chunk size       944 perslab    1110
slab class  12: chunk size      1184 perslab     885
slab class  13: chunk size      1480 perslab     708
slab class  14: chunk size      1856 perslab     564
slab class  15: chunk size      2320 perslab     451
slab class  16: chunk size      2904 perslab     361
slab class  17: chunk size      3632 perslab     288
slab class  18: chunk size      4544 perslab     230
slab class  19: chunk size      5680 perslab     184
slab class  20: chunk size      7104 perslab     147
slab class  21: chunk size      8880 perslab     118
slab class  22: chunk size     11104 perslab      94
slab class  23: chunk size     13880 perslab      75
slab class  24: chunk size     17352 perslab      60
slab class  25: chunk size     21696 perslab      48
slab class  26: chunk size     27120 perslab      38
slab class  27: chunk size     33904 perslab      30
slab class  28: chunk size     42384 perslab      24
slab class  29: chunk size     52984 perslab      19
slab class  30: chunk size     66232 perslab      15
slab class  31: chunk size     82792 perslab      12
slab class  32: chunk size    103496 perslab      10
slab class  33: chunk size    129376 perslab       8
slab class  34: chunk size    161720 perslab       6
slab class  35: chunk size    202152 perslab       5
slab class  36: chunk size    252696 perslab       4
slab class  37: chunk size    315872 perslab       3
slab class  38: chunk size    394840 perslab       2
slab class  39: chunk size    493552 perslab       2
slab class  40: chunk size    616944 perslab       1
slab class  41: chunk size    771184 perslab       1
slab class  42: chunk size   1048576 perslab       1
<26 server listening (auto-negotiate)
<27 server listening (auto-negotiate)
<28 send buffer was 212992, now 268435456
<32 send buffer was 212992, now 268435456
<31 server listening (udp)
<35 server listening (udp)
<30 server listening (udp)
<34 server listening (udp)
<29 server listening (udp)
<33 server listening (udp)
<28 server listening (udp)
<32 server listening (udp)

从日志信息中，我们可以了解到很多东西

首先就是memcached的内存管理机制，memcached会将内存分为数个大小相等的slab，每个slab又按固定大小分成数个chunk，随着slab编号的增加，slab中chunk的大小按一定比率增长

从日志中可以看到，memcached将内存分为了42个大小均为1M的slab，而每个slab又分为大小相同的数个chunk，比如slab1中每个chunk的大小为120B，slab1中总共有8738个这样的chunk，而slab42中每个chunk的大小为1M，所以slab42中只能有一个chunk，随着slab编号的增加，slab中chunk的大小按1.25的比率增长（slab1：120，slab2：150，150/120=1.25，正好是-f指定的增长因子的默认值）

slab5中每个chunk的大小为240B，当我要存放200B的数据时，则会选择slab5中的一个chunk存放数据，如果slab5中的chunk都被使用了怎么办？没关系，找到一个最近最少使用（LRU：least recently used）的chunk，将新数据存入其中，即使slab6中有空闲的chunk，因此当memcached中保存数据的大小基本一致时，增长因子过大将导致memcahed的内存使用率并不是很高

查看进程发现服务启动成功：

sean@sean:/usr/local/bin$ ps -ef|grep memcached
sean      17944   8981  0 21:28 ?        00:00:00 ./memcached -m 64 -p 9999 -u root -d -vvv
sean      17951  14900  0 21:28 pts/15   00:00:00 grep --color=auto memcached

三，基本memcached命令

由于memcached服务监听9999端口，我们可以通过telnet的方式连接至memcached

sean@sean:~$ telnet 127.0.0.1 9999
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.

之后可以通过输入相应的命令进行操作

新增：add key flag expire length

add name 1 0 4
sean
STORED

flag必须为一个正整数，将对象、数组序列化后存入缓存，当需要取出时，还需反序列化，这时可根据flag的值进行相应的反序列化，比如flag的值是1，不需要反序列化，值为2，反序列化对象，值为3，反序列化数组

length为缓存的字节长度

查询：get key

get name
VALUE name 1 4
sean
END

删除：delete key

delete name
DELETED

替换（key必须存在才能替换）：replace key flag expire length

设置（key不存在执行新增，key存在执行替换）：set key flag expire length

查看状态：stat

stats
STAT pid 18178
STAT uptime 1160
STAT time 1463495507
STAT version 1.4.25
STAT libevent 1.4.14b-stable
STAT pointer_size 64
STAT rusage_user 0.000000
STAT rusage_system 0.040000
STAT curr_connections 10
STAT total_connections 11
STAT connection_structures 11
STAT reserved_fds 20
STAT cmd_get 6
STAT cmd_set 7
STAT cmd_flush 0
STAT cmd_touch 0
STAT get_hits 4
STAT get_misses 2
STAT delete_misses 0
STAT delete_hits 2
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 264
STAT bytes_written 203
STAT limit_maxbytes 67108864
STAT accepting_conns 1
STAT listen_disabled_num 0
STAT time_in_listen_disabled_us 0
STAT threads 4
STAT conn_yields 0
STAT hash_power_level 16
STAT hash_bytes 524288
STAT hash_is_expanding 0
STAT malloc_fails 0
STAT bytes 73
STAT curr_items 1
STAT total_items 6
STAT expired_unfetched 0
STAT evicted_unfetched 0
STAT evictions 0
STAT reclaimed 0
STAT crawler_reclaimed 0
STAT crawler_items_checked 0
STAT lrutail_reflocked 0
END

通过get_hits/(get_hits + get_misses)能够计算出缓存命中率