memcached是一套分布式的高速缓存系统，由LiveJournal的Brad Fitzpatrick开发，但被许多网站使用。这是一套开放源代码软件，以BSD license授权发布。

memcached缺乏认证以及安全管制，这代表应该将memcached服务器放置在防火墙后。

memcached的API使用三十二比特的循环冗余校验（CRC-32）计算键值后，将数据分散在不同的机器上。当表格满了以后，接下来新增的数据会以LRU机制替换掉。由于memcached通常只是当作缓存系统使用，所以使用memcached的应用程序在写回较慢的系统时（像是后端的数据库）需要额外的代码更新memcached内的数据。

memcached作为缓存文件服务，默认是操作系统里面是可以直接yum -y install memcached进行安装的。

/etc/init.d/memcached 是属于系统shell编写的管理脚本，下面这个脚本是python脚本编写出来的memcached管理脚本，和shell编写的脚本实现的效果一样。

代码如下

#!/usr/bin/pythonimport sysimport osfrom subprocess import Popen,PIPEclass Process(object): '''memached rc script''' args = {'USER':'memcached', 'PORT':11211, 'MAXCONN':1024, 'CACHESIZE':64, 'OPTION':''} def __init__(self,name,program,workdir): self.name = name self.program = program self.workdir = workdir def _init(self): '''/var/tmp/memcached''' if not os.path.exists(self.workdir): os.mkdir(self.workdir) os.chdir(self.workdir) def _pidFile(self): '''/var/tmp/memcached/memcached.pid''' return os.path.join(self.workdir, "%s.pid" % self.name) def _writePid(self): if self.pid: with open(self._pidFile(),'w') as fd: fd.write(str(self.pid)) def _readConf(self,f): with open(f) as fd: lines = fd.readlines() return dict([ i.strip().replace('"','').split('=') for i in lines]) def _parseArgs(self): conf = self._readConf('/etc/sysconfig/memcached') if 'USER' in conf: self.args['USER'] = conf['USER'] if 'PORT' in conf: self.args['PORT'] = conf['PORT'] if 'MAXCONN' in conf: self.args['MAXCONN'] = conf['MAXCONN'] if 'CACHESIZE' in conf: self.args['CACHESIZE'] = conf['CACHESIZE'] options = ['-u',self.args['USER'], '-p',self.args['PORT'], '-m',self.args['CACHESIZE'], '-c',self.args['MAXCONN']] os.system("chown %s %s" % (self.args['USER'],self.workdir)) return options def start(self): pid = self._getPid() if pid: print "%s is running..." % self.name sys.exit() self._init() cmd = [self.program] + self._parseArgs() + ['-d','-P',self._pidFile()] p = Popen(cmd,stdout=PIPE) #self.pid = p.pid #self._writePid() print "%s start Sucessful \t\t [OK]" % self.name def _getPid(self): p = Popen(['pidof',self.name],stdout=PIPE) pid = p.stdout.read().strip() return pid def stop(self): pid = self._getPid() if pid: os.kill(int(pid),15) if os.path.exists(self._pidFile()): os.remove(self._pidFile()) print "%s is stopped \t\t\t [OK]" % self.name def restart(self): self.stop() self.start() def status(self): pid = self._getPid() if pid: print "%s is already running" % self.name else: print "%s is not running" % self.name def help(self): print "Usage:%s {start|stop|status|restart|} " % __file__ def main(): name = 'memcached' prog = '/usr/bin/memcached' args = '-u nobody -p 11211 -c 1024 -m 64' wd = '/var/tmp/memcached' pm = Process(name = name, program = prog, workdir = wd) try: cmd = sys.argv[1] except IndexError,e: print "Option error" sys.exit() if cmd == 'start': pm.start() elif cmd == 'stop': pm.stop() elif cmd == 'restart': pm.restart() elif cmd == 'status': pm.status() else: pm.help()if __name__ == '__main__': main()

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