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)
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