试用memcached

Memcached是一个key-value的内存数据库，提供快速缓存数据的功能，接口简单易用。

系统环境ubuntu 64位，kernel 3.8.0-30，首先安装memcached。

sudo apt-get install memcached

memcached的版本是1.4.14。然后启动，全部默认参数

memcached start

其实，memcached的参数还是挺多的，可以-h查看，挑几个常用的列举一下

-p <num>      TCP port number to listen on (default: 11211)
-U <num>      UDP port number to listen on (default: 11211, 0 is off)
-s <file>     UNIX socket path to listen on (disables network support)
-a <mask>     access mask for UNIX socket, in octal (default: 0700)
-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
-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: 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)
-h            print this help and exit
-f <factor>   chunk size growth factor (default: 1.25)
-n <bytes>    minimum space allocated for key+value+flags (default: 48)
-L            Try to use large memory pages (if available). Increasing
              the memory page size could reduce the number of TLB misses
              and improve the performance. In order to get large pages
              from the OS, memcached will allocate the total item-cache
              in one large chunk.
-t <num>      number of threads to use (default: 4)
-R            Maximum number of requests per event, limits the number of
              requests process for a given connection to prevent 
              starvation (default: 20)
-C            Disable use of CAS

然后用telnet就能用了

telnet localhost 11211
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
set hello 0 0 3
123
STORED
get hello
VALUE hello 0 3
123
END
incr hello 1
124

很明显，memcached把hello这个变量当做数值类别来用了，不过似乎并不完全是数值类别，如下

append hello 0 0 1
a
STORED
get hello
VALUE hello 0 4
124a
END2
incr hello 1
CLIENT_ERROR cannot increment or decrement non-numeric value

在hello后面append了一个字符串，依然能够work，但是再次incr就不行了，说明memcached并不苛求存储value的类型。在使用set的时候，后面跟着一些数字，这些都是表示key的设定的。

set hello <flag> <expires> <byte>
get hello
VALUE 123 <flag> <byte>

flag: 0-不压缩，1-压缩
expires: key在多久之后删除，以秒为单位，0是不删除
byte: value的字节数

get的时候可以获得key的flag和byte设定。

当然，如果这样的一个工具只有telnet这样的接口肯定是不行的，试用一下ruby的接口

require "rubygems"
require "memcache"

server = ['localhost:11211']
option = {}

myCache = MemCache.new(server, option)

# save data
myCache['key1'] = 11111
myCache['key2'] = "aaaaa"
myCache['key3'] = %w[abc 123abc]
myCache['key4'] = {:foo => 1, :bar => 'a'}

# get data
puts (myCache['key1'])
puts (myCache['key2'])
puts (myCache['key3'])
puts (myCache['key4'])

 以下是输出，

11111
aaaaa
abc
123abc
{:foo=>1, :bar=>"a"}

看起来似乎没什么特别的地方，去memcached上看一下

telnet localhost 11211
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
get key1
VALUE key1 0 6
ig+
END
get key2
VALUE key2 0 15
I"
aaaaa:EF
END
get key3
VALUE key3 0 28
[Iabc:EFI"
            123abc;F
END
get key4
VALUE key4 0 25
{fooibarI"a:EF
END

显示中夹杂着很多乱码和不可见ASCII字符，明显这是ruby的memcached-client序列化之后的结果。