django mysql mongodb_Nginx+uWsgi+Django+Python+MongoDB+mySQL服务器搭建

搭建目标如下:

django mysql mongodb_Nginx+uWsgi+Django+Python+MongoDB+mySQL服务器搭建_第1张图片

图:系统架构图

这个系统可以提供web服务及其它查询应用服务,我用其做一个二手房信息搜集、处理及分发的系统,可以通过浏览器访问,也可以通过定制的客户端进行访问。

一、安装篇

1、下载安装python

# wget http://www.python.org/ftp/python/2.7.3/Python-2.7.3.tgz

#

#tar xvfz Python-2.7.3.tgz

# cd Python-2.7.3#./configure

#make#sudo make install

下面是一些python安装工具,可以方便的安装所缺模块

python的包管理setuptools安装

# wget http://peak.telecommunity.com/dist/ez_setup.py

# python ez_setup.py

python的包管理pip安装(需要先安装setuptools)

# wget http://python-distribute.org/distribute_setup.py

# python distribute_setup.py

#wget https://github.com/pypa/pip/raw/master/contrib/get-pip.py

# python get-pip.py

下面使用pip 安装readline

# sudo pip install readline

2、下载安装Django

# wget https://www.djangoproject.com/download/1.4.3/tarball/

#

#tar xvfz Django-1.4.3.tar.gz

# cd Django-1.4.3#sudo python setup.py install

3、下载安装MongoDB

l  先下载安装scons

# wget http://sourceforge.net/projects/scons/files/scons/2.1.0.alpha.20101125/scons-2.1.0.alpha.20101125.tar.gz/download

#

#tar xvfz scons-2.1.0.alpha.20101125.tar.gz

# cd scons-2.1.0.alpha.20101125#sudo python setup.py install

l  下载安装MongoDB

# wget http://downloads.mongodb.org/src/mongodb-src-r2.2.2.tar.gz

#

#tar xvfz mongodb-src-r2.2.2.tar.gz

# cd mongodb-src-r2.2.2# scons all

#sudo scons --prefix=/usr/local/mongodb --full install

l  下载安装pyMongo

# wget wget http://pypi.python.org/packages/source/p/pymongo/pymongo-2.4.2.tar.gz

#

#tar xvfz pymongo-2.4.2.tar.gz

# cd pymondo-2.4.2#sudo python setup.py install

测试pyMongo是否安装成功

#python

> import pymongo

如果没有返回错误,则表明安装成功。

l  下载安装mongoengine【暂时没有用到】

# wget http://github.com/mongoengine/mongoengine/tarball/v0.6.20 --no-check-certificate

#

#tar xvfz v0.6.20# cd MongoEngine-mongoengine-9cc6164

#sudo python setup.py install

测试mongoengine是否安装成功

#python

> from mongoengine import connect

如果没有返回错误,则表明安装成功。

4、下载安装MySQL

l  先下载安装cmake:

# wget http://www.cmake.org/files/v2.8/cmake-2.8.8.tar.gz

#

#tar xvfz cmake-2.8.8.tar.gz

# cd cmake-2.8.8#./configure

#make#sudo make install

l  下载安装mysql

# wget http://cdn.mysql.com/Downloads/MySQL-5.5/mysql-5.5.29.tar.gz

#

#tar xvfz mysql-5.5.29.tar.gz

# cd mysql-5.5.29# cmake .-DCMAKE_INSTALL_PREFIX=/usr/local/mysql -DMYSQL_DATADIR=/usr/localmysql/data/ -DMYSQL_UNIX_ADDR=/usr/localmysql/data/mysqld.sock -DWITH_INNOBASE_STORAGE_ENGINE=1 -DSYSCONFDIR=/etc -DEXTRA_CHARSETS=all -DDEFAULT_CHARSET=utf8 -DDEFAULT_COLLATION=utf8_unicode_ci -DWITH_DEBUG=0#make#sudo make install

l  下载安装mysql-python

# wget http://sourceforge.net/projects/mysql-python/files/mysql-python/1.2.3/MySQL-python-1.2.3.tar.gz

#

#tar xvfz MySQL-python-1.2.3.tar.gz

# cd MySQL-python-1.2.3

在安装前,需要修改site.py中mysql_config的路径(为mysql安装路径下的/bin/mysql_config),

#site.py

mysql_config = /usr/local/mysql/bin/mysql_config

更改完后,可以进行编译和安装了

# python setup.py build

#sudo python setup.py install

通过测试import MySQLdb来判断是否安装成功,这里还需要将mysql安装路径下的lib加入到环境变量LD_LIBRARY_PATH中。

# export LD_LIBRARY_PATH=/usr/local/mysql/lib/:$LD_LIBRARY_PATH

注:cmake选项说明

选项

说明

-DCMAKE_INSTALL_PREFIX

mysql安装的主目录。默认为/usr/local/mysql

-DMYSQL_DATADIR

mysql数据保存的路径自定义

-DMYSQL_UNIX_ADDR

系统Socket文件(.sock)设置基于该文件路径进行Socket连接必要为绝对路径

-DWITH_INNOBASE_STORAGE_ENGINE

存储引擎设置

-DSYSCONFDIR

mysql配置文件my.cnf地址默认/etc下

-DMYSQL_TCP_PORT

数据库服务器TCP/IP连接的监听端口默认为3306

-DEXTRA_CHARSETS

-DDEFAULT_CHARSET

-DDEFAULT_COLLATION

数据库编码设置

-DENABLED_LOCAL_INFILE

默认为关闭这里开启

-DWITH_DEBUG

DEBUG开关,默认为关

5、下载安装uWsgi

# wget http://projects.unbit.it/downloads/uwsgi-1.2.3.tar.gz

#

#tar xvfz uwsgi-1.2.3.tar.gz

# cd uwsgi-1.2.3# python uwsgiconfig.py--build

二、配置篇

1、配置nginx(配置nginx.conf)

server {

listen8080;

server_name django;

location/{

root/data/htdocs/django;

include uwsgi_params;

uwsgi_pass127.0.0.1:8000;

}

access_log/data/htdocs/django/access.log;

}

2、配置uWsgi

可以将uwsgi的配置文件做成ini格式的,也可以直接在命令行进行输入,下面给出了ini文件形式的配置

#uwsgi.ini

[uwsgi]

socket= 127.0.0.1:8000file=/data/htdocs/django/django_uwsgi.py

pidfile= /data/htdocs/django/django_uwsgi.pid

master=true

workers= 4daemonize= /data/htdocs/django/django_uwsgi.log

其中django.py是我们需要自己定义的,它是用来将uwsgi与django进行连接的。

#django_uwsgi.py#!/usr/bin/python

importos, sysfrom django.core.handlers.wsgi importWSGIHandlerif not os.path.dirname(__file__) in sys.path[:1]:

sys.path.insert(0, os.path.dirname(__file__))

os.environ['DJANGO_SETTINGS_MODULE'] = 'mysites.settings'    #设置配置文件application= WSGIHandler()                      #调用django的处理函数WSGIHandler

3、配置mySQL

在安装完成后,创建mysql用户,并将mysql的目录拥有者换成mysql和mysql所属的group,并设置数据库的用户名和data的路径。

# groupadd mysql

# useradd-g mysql mysql

#chown mysql.mysql -R /service/mysql/#/usr/local/mysql/scripts/mysql_install_db --user=mysql --basedir=/usr/local/mysql --datadir=/usr/local/mysql/data

将配置文件拷贝到/etc/下,并重命名为my.conf

# cp /usr/local/mysql/support-files/my-medium.cnf /etc/my.cnf

4、配置Django连接MySQL

在安装完成后,需要创建运行环境

# python manage.py startproject

执行后,会在创建一个文件manage.py和一个目录mysite,mysite目录中有urls.py,__init__.py,settings.py和wsgi.py文件。我们通过修改settings.py文件中的部分配置来连接mysql数据库。

假设在mysql中,创建了一个数据库test_python,并添加了一个用户名python_user且密码为python_user,而我们连接地址为192.168.1.2的mysql服务器,端口为3306(默认),则更改settings.py如下:

...

DATABASES={'default': {'ENGINE': 'django.db.backends.mysql', # Add 'postgresql_psycopg2', 'mysql', 'sqlite3' or 'oracle'.'NAME': 'test_python', # Or path to database file ifusing sqlite3.'USER': 'python_user', # Not used with sqlite3.'PASSWORD': 'python_user', # Not used with sqlite3.'HOST': '192.168.1.2', # Set to empty string forlocalhost. Not used with sqlite3.'PORT': '3306', # Set to empty string fordefault. Not used with sqlite3.

}

}

...

通过django中的manage.py进行验证

# python manage.py shell>>from django.db import connection>> cursor = connection.cursor()

如果成功,则表明连接数据库成功,其余的关于django的使用在此不多介绍。

5、配置Django连接MongoDB

这里可以直接使用PyMongo模块,也可以使用第三方的中间件mongoengine,PyMongo使用方法的介绍有很多,可以直接查看官方文档http://api.mongodb.org/python/current/api/pymongo/connection.html。

这里主要介绍mongoengine的配置方法

首先,要在settings中设置一个包含数据库信息的别名,在连接时会用到

DATABASES ={

...'MongoDB': {'ENGINE': 'django_mongodb_engine','NAME':'test',

}

}

...

其中NAME指的是database的名字。

如果你想使用 django 的 session 和 authentication 这两个框架, 还要加入

# add session

SESSION_ENGINE= 'mongoengine.django.sessions'# add authentication

AUTHENTICATION_BACKENDS= ('mongoengine.django.auth.MongoEngineBackend',

)

然后就可以使用mongoengine了。

from mongoengine import *from mysite.settings import DATABASES

conn= connect('MongoDB', ip="127.0.0.1", port=27017)

这里使用了settings中定义的别名'MongoDB'。

三、启动篇

1、启动Django服务

启动Django服务进程

# python manage.py runserver 0.0.0.0:8000

2、启动mongoDB服务进程

# /usr/local/mongodb/bin/mongod --port=27000 --dbpath=$HOME/data/ --logpath=$HOME/data/mongo.log

3、启动mysql服务

# /etc/init.d/mysqld start

四、实例篇

1、通过django的模板和mysql数据库中的数据,生成一个包含人名及信息表格的html页面

首先,我们先在数据库中建立一个表peoples,并插入三条数据

mysql> create table peoples (id int auto_increment primary key, name char(30), age int, birth date);

mysql>mysql> insert into peoples(name, age, birth) values('zhangsan', 30,'1983-1-1'),('lisi', 29, '1984-1-1'), ('wangwu', 28, '1985-1-1');

然后做一个html页面模板,名为peoples_list.html,内容如下:

NameAgeBirth{% for people in peoples_list %}{{ people.0 }}{{ people.1 }}{{ people.2 }}{% endfor %}

接下来是完成业务逻辑,保存在文件peoples.py中(使用了django自带的数据库管理模块)

#!/bin/python

#!/bin/python2#-*- coding: utf-8 -*-

from django.db importconnectionfrom django.shortcuts importrender_to_responsedefpeoples_list(request):

cursor=connection.cursor()

cursor.execute('select name,age,birth from peoples')

peoples=cursor.fetchall()return render_to_response('peoples_list.html', {'peoples_list':peoples})

最后修改urls.py中的配置,标红的就是修改的内容

from django.conf.urls importpatterns, include, urlfrom peoples import peoples_list#Uncomment the next two lines to enable the admin:#from django.contrib import admin#admin.autodiscover()

urlpatterns= patterns('',#Examples:

#url(r'^$', 'mysite.views.home', name='home'),

#url(r'^mysite/', include('mysite.foo.urls')),

#Uncomment the admin/doc line below to enable admin documentation:

#url(r'^admin/doc/', include('django.contrib.admindocs.urls')),

#Uncomment the next line to enable the admin:

#url(r'^admin/', include(admin.site.urls)),

url(r'peoples_list/$', peoples_list),

)

通过浏览器访问对应的地址就能看到最终的结果

django mysql mongodb_Nginx+uWsgi+Django+Python+MongoDB+mySQL服务器搭建_第2张图片

2、使用MySQLdb来完成上面的业务逻辑

业务逻辑保存在peoples_mysqldb.py中

#!/bin/python#-*- coding: utf8 -*-

from django.shortcuts importrender_to_responseimportMySQLdbdefpeoples_list_mysqldb(request):

conn= MySQLdb.connect(host='127.0.0.1', port=3306, user='python_user', passwd='python_user', db='test_python', charset='utf8')

cursor=conn.cursor()

sqlComm= "select name, age, birth from peoples"cursor.execute(sqlComm)

peoples=cursor.fetchall()

cursor.close()

conn.close()return render_to_response('peoples_list.html', {'peoples_list':peoples})

修改urls.py

from django.conf.urls importpatterns, include, url#from view import current_datetimefrom peoples_mysqldb import peoples_list_mysqldb#Uncomment the next two lines to enable the admin:#from django.contrib import admin#admin.autodiscover()

urlpatterns= patterns('',#Examples:

#url(r'^$', 'mysite.views.home', name='home'),

#url(r'^mysite/', include('mysite.foo.urls')),

#Uncomment the admin/doc line below to enable admin documentation:

#url(r'^admin/doc/', include('django.contrib.admindocs.urls')),

#Uncomment the next line to enable the admin:

#url(r'^admin/', include(admin.site.urls)),

url(r'peoples_list_mysqldb/$', peoples_list_mysqldb)

)

最终的结果为:

django mysql mongodb_Nginx+uWsgi+Django+Python+MongoDB+mySQL服务器搭建_第3张图片

3、将数据库数据以json形式返回

主要是业务逻辑代码的编写:test_json.py

#coding: utf-8#!/bin/python

from django.utils importsimplejsonfrom django.http importHttpResponsefrom django.db importconnectiondefjson_peoples(request):

cursor=connection.cursor()

cursor.execute('select name, age, birth from peoples')

peoples=cursor.fetchall()

i=0

json_peoples={}

names=locals()for people inpeoples:

tag= 'person%s' %i

names[tag]= {'name':people[0], 'age':people[1], 'birth':str(people[2])}

json_peoples[tag]=names[tag]

i= ((i+1))

json= {'person':i}

json['person_info'] =json_peoples

cursor.close()return HttpResponse(simplejson.dumps(json, ensure_ascii=False, sort_keys=True))

向urls中添加该对应关系

from django.conf.urls importpatterns, include, url#from view import current_datetime

from json_test import json_peoples#Uncomment the next two lines to enable the admin:#from django.contrib import admin#admin.autodiscover()

urlpatterns= patterns('',#Examples:

#url(r'^$', 'mysite.views.home', name='home'),

#url(r'^mysite/', include('mysite.foo.urls')),

#Uncomment the admin/doc line below to enable admin documentation:

#url(r'^admin/doc/', include('django.contrib.admindocs.urls')),

#Uncomment the next line to enable the admin:

#url(r'^admin/', include(admin.site.urls)),

url(r'peoples_json/$', json_peoples)

)

最终效果为:

7742c18f970a0b9a8208e62083cb0fbc.png

4、通过pymongo模块访问mongodb,将结果返回成一个页面

模板还是使用第一个例子的,只要重新写一个业务逻辑即可mongodb_test.py

#!/bin/python2#-*- coding: utf-8 -*-

from django.db importconnectionfrom django.shortcuts importrender_to_responsedefpeoples_list(request):

cursor=connection.cursor()

cursor.execute('select name,age,birth from peoples')

peoples=cursor.fetchall()printpeoplesreturn render_to_response('peoples_list.html', {'peoples_list':peoples})

向urls.py中添加对应关系

from django.conf.urls importpatterns, include, url#from view import current_datetime

from mongodb_test import mongodb_peoples#Uncomment the next two lines to enable the admin:#from django.contrib import admin#admin.autodiscover()

urlpatterns= patterns('',#Examples:

#url(r'^$', 'mysite.views.home', name='home'),

#url(r'^mysite/', include('mysite.foo.urls')),

#Uncomment the admin/doc line below to enable admin documentation:

#url(r'^admin/doc/', include('django.contrib.admindocs.urls')),

#Uncomment the next line to enable the admin:

#url(r'^admin/', include(admin.site.urls)),

url(r'peoples_mongo/$', mongodb_peoples)

)

最终结果为

django mysql mongodb_Nginx+uWsgi+Django+Python+MongoDB+mySQL服务器搭建_第4张图片

五、性能

由于系统中有nginx,uwsgi,django,mysql和mongodb模块,所以分别对几种情况下做了一下简单的性能测试。

测试环境:2核Intel(R) Xeon(R) CPU E5645,4G内存,上述所有模块在一台服务器上运行。

采用了并发500,持续30秒的测试压力。

测试nginx:

./superwebbench -c 500 -t 30 http://127.0.0.1:8000/

SuperWebBench- Advanced Simple Web Benchmark 0.1Copyright (c) Radim Kolar1997-2004, GPL Open Source Software.

Modified By Davelv2011-11-03Benchmarking:GET http://127.0.0.1:8000/ (using HTTP/1.1)

500 clients, running 30sec.

Speed=6080 pages/sec, 4998280 bytes/sec.

Requests:182419 ok, 0 http error, 0 failed.

测试nginx+uwsgi:(将uwsgi的文件指向一个直接返回http响应的python脚本)

用于返回包含当前时间的HTML页面的Python脚本:

#coding: utf-8#!/usr/local/bin/python

importdatetimedefapplication(environ, start_response):

cur=datetime.datetime.now()

response_body= """

""" %cur

status= '200 OK'response_headers= [('Content-Type', 'text/plain'), ('Content-Length', str(len(response_body)))]

start_response(status, response_headers)return [response_body]

结果:

./superwebbench -c 500 -t 30 http://127.0.0.1:8000/

SuperWebBench- Advanced Simple Web Benchmark 0.1Copyright (c) Radim Kolar1997-2004, GPL Open Source Software.

Modified By Davelv2011-11-03Benchmarking:GET http://127.0.0.1:8000/ (using HTTP/1.1)

500 clients, running 30sec.

Speed=4417 pages/sec, 1351734 bytes/sec.

Requests:132523 ok, 0 http error, 0 failed.

测试nginx+uwsgi+mysql:

用于返回包含mysql数据的HTML页面的Python脚本:

#coding: utf-8#!/usr/local/bin/python

importdatetimeimportMySQLdbdefapplication(environ, start_response):

conn= MySQLdb.connect(host='127.0.0.1', port=3306, user='python_user', passwd='python_user', db='test_python', charset='utf8')

cursor=conn.cursor()

sqlComm= "select name, age, birth from peoples"cursor.execute(sqlComm)

peoples=cursor.fetchall()

cursor.close()

conn.close()

body= "

Name Age Birth

for people inpeoples:

person= "

%s%s%s" % (str(people[0]), str(people[1]), str(people[2]))

body= body +person

body= body +"

"response_body= """

status= '200 OK'

printresponse_body

response_headers= [('Content-Type', 'text/plain'), ('Content-Length', str(len(response_body)))]printresponse_headers

start_response(status, response_headers)return [response_body]

结果

./superwebbench -c 500 -t 30 http://127.0.0.1:8000/

SuperWebBench- Advanced Simple Web Benchmark 0.1Copyright (c) Radim Kolar1997-2004, GPL Open Source Software.

Modified By Davelv2011-11-03Benchmarking:GET http://127.0.0.1:8000/ (using HTTP/1.1)

500 clients, running 30sec.

Speed=1078 pages/sec, 539381 bytes/sec.

Requests:32345 ok, 13 http error, 0 failed.

测试nginx+uwsgi+django:

./superwebbench -c 500 -t 30 http://127.0.0.1:8000/time/

SuperWebBench- Advanced Simple Web Benchmark 0.1Copyright (c) Radim Kolar1997-2004, GPL Open Source Software.

Modified By Davelv2011-11-03Benchmarking:GET http://127.0.0.1:8000/time/ (using HTTP/1.1)

500 clients, running 30sec.

Speed=652 pages/sec, 176182 bytes/sec.

Requests:19558 ok, 7 http error, 0 failed.

测试nginx+uwsgi+django+mysql:

./superwebbench -c 500 -t 30 http://127.0.0.1:8000/peoples_list/

SuperWebBench- Advanced Simple Web Benchmark 0.1Copyright (c) Radim Kolar1997-2004, GPL Open Source Software.

Modified By Davelv2011-11-03Benchmarking:GET http://127.0.0.1:8000/peoples_list/ (using HTTP/1.1)

500 clients, running 30sec.

Speed=321 pages/sec, 204044 bytes/sec.

Requests:9615 ok, 23 http error, 0 failed.

测试nginx+uwsgi+django+mongodb:

./superwebbench -c 500 -t 30 http://127.0.0.1:8000/peoples_mongo/

SuperWebBench- Advanced Simple Web Benchmark 0.1Copyright (c) Radim Kolar1997-2004, GPL Open Source Software.

Modified By Davelv2011-11-03Benchmarking:GET http://127.0.0.1:8000/peoples_mongo/ (using HTTP/1.1)

500 clients, running 30sec.

Speed=355 pages/sec, 221449 bytes/sec.

Requests:10648 ok, 15 http error, 0 failed.

总结一下,可以看出nginx的处理速度极快,而uwsgi同样也不慢,最大的瓶颈在于django,效率大概下降了70%多,而数据库查询(无论是mysql还是mongodb)也对效率有一定影响。

当然,这只是把所有服务都部署在一台服务器上,对资源的抢占也影响了系统的效率。

六、其它介绍

1、编码问题

需要注意编码问题,否则会出现乱码或者执行错误。

有四个部分需要统一编码格式(以utf8为例):

(1)    mysql数据库的编码设置(charset = ‘utf8’)

(2)    python文件的编码设置(# -*- coding:utf8 -*-)

(3)    连接mysql数据库时要加上参数charset=’utf8’

(4)    如果使用django,则需要在settings.py中添加DEFAULT_CHARSET = 'utf8'。

2、Python通过MySQLdb对MySQL的操作

导入MySQLdb模块

import MySQLdb

与数据库建立连接

conn=MySQLdb.connect([host="localhost",][port=3306,] user="root", passwd="passwd",db="database_name"[, charset=’utf8’])

其中host为mysql主机名,port为端口号,user为用户名,passwd为密码,db为数据库名,charset为编码类型

获取游标

cursor = conn.cursor()

数据库命令

插入命令

insertComm =‘insert into table_name(...) values(...)’

cursor.execute(insertComm,...)

如:(注意最后要调用commit来提交这次命令)

insertComm = 'insert into peoples(name, age, birth) values(%s, %s, %s)'param= ('zhengliu', 27, '1986-1-1')

cursor.execute(insertComm, param)

conn.commit()

更新命令

updateComm = ‘update table_name set column1=value1[,...] where column=value[,...]’

cursor.execute(updateComm)

如:(注意最后要调用commit来提交这次命令)

updateComm = "update peoples set age=%s,birth=%s where name='zhengliu'"param= (26, '1987-1-1')

cursor.execute(updateComm, param)

conn.commit()

删除命令

deleteComm = ‘delete from table_name where column1=value1[,...]’

cursor.execute(deleteComm)

如:(注意最后要调用commit来提交这次命令)

deleteComm = "delete from peoples where name=%s"param=('zhengliu')

cursor.execute(deleteComm, param)

conn.commit()

查询命令

selectComm = ‘select name, age, birth from peoples [where column1=values1,...]’

cursor.execute(selectComm)

result= cursor.fetchall()

如:

queryComm = 'select name, age, birth from peoples'cursor.execute(queryComm)

peoples= cursor.fetchall()

提交和回滚

在对数据库进行修改操作时,需要进行commit命令来最终提交数据库,如果想要取消这次操作,则要在commit前先调用rollback进行回滚操作。

conn.commit()

conn.rollback()

关闭命令

关闭游标

cursor.close()

关闭连接

conn.close()

cursor游标对象属性及方法

属性方法

描述

arraysize

使用fetchmany()方法时一次取出的记录数,默认为1

connection

创建此游标的连接(可选)

discription

返回游标的活动状态,包括(7元素):(name,type_code, display_size,internal_size,precision,scale,null_ok) 其中name,type_code是必须的。

lastrowid

返回最后更新行的ID(可选),如果数据库不支持,返回None

rowcount

最后一次execute()返回或影响的行数

callproc(func[,args])

调用一个存储过程

close()

关闭游标

execute(op[,args])

执行sql语句或数据库命令

executemany(op,args)

一次执行多条sql语句,执行的条数由arraysize给出

fetchone()

匹配结果的下一行

fetchall()

匹配所有剩余结果

fetchmany(size-cursor,arraysize)

匹配结果的下几行

__iter__()

创建迭代对象(可选,参考next())

messages

游标执行好数据库返回的信息列表(元组集合)

next()

使用迭代对象得到结果的下一行

nextset()

移动到下一个结果集(如果支持的话)

rownumber

当前结果集中游标的索引(从0行开始)

setinput-size(sizes)

设置输入最大值

setoutput-size(sizes[,col])

设置列输出的缓冲值

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