tornado--SESSION框架，一致性hash，分布式存储

预备知识

1. tornado框架session要自己写

2. cookie存储在客户端浏览器上，session数据放在服务器上

3. session依赖cookie

4. 扩展tornado，返回请求前自定义session

5. 面向对象的知识，obj['xxx']==>_getitems__,obj['xxx']=xxx ==> __setitems__, del obj['xxx'] ==> __delitems__

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class Foo(object):         def __getitem__(self, key):         print  '__getitem__',key         def __setitem__(self, key, value):         print '__setitem__',key,value         def __delitem__(self, key):         print '__delitem__',key             obj = Foo() result = obj['k1'] #obj['k2'] = 'wupeiqi' #del obj['k1']

session实现机制

1. tornado框架中，通过application的url映射到MainHandler类处理请求，根据请求的方式，通过反射执行对应的get或post等方法

2. tornado源码中有很多扩展点（钩子）供开发者使用，如在执行get或post方法之前先执行initialiaze方法，即使没有调用也执行

3. 扩展initialiaze，用户请求进来，读一下用户的cookie，如果有的话，能够拿到，没有可以创建一个

4. 为避免重复在每个映射的类里都写一遍initialiaze，可以在他们的共同的基类BaseHandler（自定义的类）里写initialiaze方法

5. 其实这些类应该继承tornado.web.RequestHandler类，让BaseHandler继承这个类，其他类也就继承了

6. initialiaze中定义了self.my_session字段，它是一个session类的对象，init中获取或创建session

7. 用户登录，通过__setitem__设置session中的内容，session保存在服务器中

8. session_container是用来保存session的字典

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import tornado.ioloop import tornado.web from hashlib import sha1 import os, time     session_container = {}     create_session_id = lambda: sha1('%s%s' % (os.urandom(16), time.time())).hexdigest()         class Session(object):         session_id = "__sessionId__"         def __init__(self, request):         session_value = request.get_cookie(Session.session_id)         if not session_value:             self._id = create_session_id()         else:             self._id = session_value         request.set_cookie(Session.session_id, self._id)         def __getitem__(self, key):         return session_container[self._id][key]         def __setitem__(self, key, value):         if session_container.has_key(self._id):             session_container[self._id][key] = value         else:             session_container[self._id] = {key: value}         def __delitem__(self, key):         del session_container[self._id][key]         class BaseHandler(tornado.web.RequestHandler):         def initialize(self):         # my_session['k1']访问 __getitem__ 方法         self.my_session = Session(self)         class MainHandler(BaseHandler):         def get(self):         print self.my_session['c_user']         print self.my_session['c_card']         self.write('index')     class LoginHandler(BaseHandler):         def get(self):         self.render('login.html', **{'status': ''})         def post(self, *args, **kwargs):             username = self.get_argument('name')         password = self.get_argument('pwd')         if username == 'wupeiqi' and password == '123':                 self.my_session['c_user'] = 'wupeiqi'             self.my_session['c_card'] = '12312312309823012'                 self.redirect('/index')         else:             self.render('login.html', **{'status': '用户名或密码错误'})     settings = {     'template_path': 'template',     'static_path': 'static',     'static_url_prefix': '/static/',     'cookie_secret': 'aiuasdhflashjdfoiuashdfiuh',     'login_url': '/login' }     application = tornado.web.Application([     (r"/index", MainHandler),     (r"/login", LoginHandler), ], **settings)         if __name__ == "__main__":     application.listen(8888)     tornado.ioloop.IOLoop.instance().start()

session分布式

1. session可以存在其它地方，如redis，数据库，mongo等等

2. 当session规模达到很大数量级，就采用多台分布式存储，经过一致性hash算法，分配到对应的机器上

3. 根据cookie字符串转换成一串数字，每台机器分管的数字段区域不同，权重大的管的大

一致性哈希​

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#!/usr/bin/env python #coding:utf-8   import sys import math from bisect import bisect     if sys.version_info >= (2, 5):     import hashlib     md5_constructor = hashlib.md5 else:     import md5     md5_constructor = md5.new     class HashRing(object):     """一致性哈希"""           def __init__(self,nodes):         '''初始化         nodes : 初始化的节点，其中包含节点已经节点对应的权重                 默认每一个节点有32个虚拟节点                 对于权重，通过多创建虚拟节点来实现                 如：nodes = [                         {'host':'127.0.0.1:8000','weight':1},                         {'host':'127.0.0.1:8001','weight':2},                         {'host':'127.0.0.1:8002','weight':1},                     ]         '''                   self.ring = dict()         self._sorted_keys = []           self.total_weight = 0                   self.__generate_circle(nodes)                                           def __generate_circle(self,nodes):         for node_info in nodes:             self.total_weight += node_info.get('weight',1)                       for node_info in nodes:             weight = node_info.get('weight',1)             node = node_info.get('host',None)                               virtual_node_count = math.floor((32*len(nodes)*weight) / self.total_weight)             for i in xrange(0,int(virtual_node_count)):                 key = self.gen_key_thirty_two( '%s-%s' % (node, i) )                 if self._sorted_keys.__contains__(key):                     raise Exception('该节点已经存在.')                 self.ring[key] = node                 self._sorted_keys.append(key)                   def add_node(self,node):         ''' 新建节点         node : 要添加的节点，格式为：{'host':'127.0.0.1:8002','weight':1}，其中第一个元素表示节点，第二个元素表示该节点的权重。         '''         node = node.get('host',None)         if not node:                 raise Exception('节点的地址不能为空.')                           weight = node.get('weight',1)                   self.total_weight += weight         nodes_count = len(self._sorted_keys) + 1                   virtual_node_count = math.floor((32 * nodes_count * weight) / self.total_weight)         for i in xrange(0,int(virtual_node_count)):             key = self.gen_key_thirty_two( '%s-%s' % (node, i) )             if self._sorted_keys.__contains__(key):                 raise Exception('该节点已经存在.')             self.ring[key] = node             self._sorted_keys.append(key)               def remove_node(self,node):         ''' 移除节点         node : 要移除的节点 '127.0.0.1:8000'         '''         for key,value in self.ring.items():             if value == node:                 del self.ring[key]                 self._sorted_keys.remove(key)           def get_node(self,string_key):         '''获取 string_key 所在的节点'''         pos = self.get_node_pos(string_key)         if pos is None:             return None         return self.ring[ self._sorted_keys[pos]].split(':')           def get_node_pos(self,string_key):         '''获取 string_key 所在的节点的索引'''         if not self.ring:             return None                       key = self.gen_key_thirty_two(string_key)         nodes = self._sorted_keys         pos = bisect(nodes, key)         return pos           def gen_key_thirty_two(self, key):                   m = md5_constructor()         m.update(key)         return long(m.hexdigest(), 16)               def gen_key_sixteen(self,key):                   b_key = self.__hash_digest(key)         return self.__hash_val(b_key, lambda x: x)       def __hash_val(self, b_key, entry_fn):         return (( b_key[entry_fn(3)] << 24)|(b_key[entry_fn(2)] << 16)|(b_key[entry_fn(1)] << 8)| b_key[entry_fn(0)] )       def __hash_digest(self, key):         m = md5_constructor()         m.update(key)         return map(ord, m.digest())     """ nodes = [     {'host':'127.0.0.1:8000','weight':1},     {'host':'127.0.0.1:8001','weight':2},     {'host':'127.0.0.1:8002','weight':1}, ]   ring = HashRing(nodes) result = ring.get_node('98708798709870987098709879087') print result   """   一致性哈希

session

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from hashlib import sha1 import os, time     create_session_id = lambda: sha1('%s%s' % (os.urandom(16), time.time())).hexdigest()     class Session(object):       session_id = "__sessionId__"       def __init__(self, request):         session_value = request.get_cookie(Session.session_id)         if not session_value:             self._id = create_session_id()         else:             self._id = session_value         request.set_cookie(Session.session_id, self._id)       def __getitem__(self, key):         # 根据 self._id ，在一致性哈西中找到其对应的服务器IP         # 找到相对应的redis服务器，如： r = redis.StrictRedis(host='localhost', port=6379, db=0)         # 使用python redis api 链接         # 获取数据，即：         # return self._redis.hget(self._id, name)       def __setitem__(self, key, value):         # 根据 self._id ，在一致性哈西中找到其对应的服务器IP         # 使用python redis api 链接         # 设置session         # self._redis.hset(self._id, name, value)         def __delitem__(self, key):         # 根据 self._id 找到相对应的redis服务器         # 使用python redis api 链接         # 删除，即：         return self._redis.hdel(self._id, name)

来自为知笔记(Wiz)