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/python
import sys
import os
from subprocess import Popen,PIPE
class 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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