python 使用memcached

python 使用memcached

分类：技术论坛 | 标签： memcached  python 

2007-09-11 18:02 阅读(3289)评论(1)

网上对memcached的讨论好火呀！总结一下

安装 memcached：
1、下载memcached-1.2.2.tar.gz
2、tar xvzf memcached-1.2.2.tar.gz
3、./configure;make;make install

安装python API组件：
1、下载python-memcached-1.39.tar.gz
2、tar xvzf python-memcached-1.39.tar.gz
3、python setup.py install

启动memcached
memcached -d -m 64 -l 10.1.41.113 -p 11211
启动的这个memcached为一个后台守护进程模式（-d), 然后缓存的空间为64M（-m), 监听(-l)服务器10.1.41.113的11212号端口(-p)
root下要加-u 指定user参数
memcached -u bj1822 -d -m 64 -l 10.1.41.113 -p 11211

memcached -h
memcached 1.2.2
-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)
-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
-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

编写python程序：
import memcache, time
mc = memcache.Client(['10.1.41.113:11211'], debug=0)
连接到10.1.41.113的11211端口，也就是memcachd启动的端口。

mc.set("some_key", "Some value")
设置key和value，第三个参数默认为0，也就是数据永不超时。
如果这样设置：
mc.set("some_key", "Some value",1)
表示一秒后超时
过两秒打印value的话
time.sleep ( 2)
value = mc.get("some_key")
print value
结果就是None了。

删除
mc.set("another_key", 3)                                                                          mc.delete("another_key")                                                                                                          
自增和自减
mc.set("key", "1")                                                                                mc.incr("key")                                                                                     mc.decr("key")          

关于LRU
LRU是缓冲超过存储上限时删掉队尾也就是最长时间没人访问的元素，参数是-M。但设置了-M和过期时效会存在将未失效的元素删去的风险。所以网上有人改了下代码，增加对过期时效的判断：

返回超时时间的代码：
if (exptime > REALTIME_MAXDELTA) 
     return (rel_time_t) (exptime - stats.started);  
else { 
     return (rel_time_t) (exptime + current_time); 
}
memcached的失效时间格式有两种，当大于60*60*24*30也就是30天的秒数时就是过期距1970年1月1日零时的秒数，否则是有效的秒数。

删除cache的代码：
for (search = tails[id]; tries>0 && search; tries--, search=search->prev) { 
 if (search->refcount==0) { 
  item_unlink(search); 
   break; 
  } 
}
增加条件：
search->exptime && search->exptime <= current_time 
这样就可以保证删除的都是过期了的元素了。