python连接mysql,并在中间用memcached保存sql结果

时间:2021-01-04 08:46:23

我在python和mysql中间加了一层memcached中间层,缓存sql查询的结果,以期望获得更好的系统性能。

参考:

http://www.cnblogs.com/rollenholt/archive/2012/05/29/2524327.html

http://www.the5fire.com/python-opt-mysql.html

python连接mysql需要先安装一些lib,我是ubuntu,比较easy,直接apt-get

sudo apt-get install libmysqld-dev
sudo apt-get install libmysqlclient-dev
sudo apt-get install python-mysqldb

然后就可以写python去connect mysql啦,当然,一开始,mysql的数据库里面是神马也没有的,要自己先去create一个数据库,然后再create table,insert data。下面是建表和插入数据的python代码

 1 #!/usr/bin/env python
 2 
 3 # 20140105,  create_table.py
 4 
 5 import MySQLdb
 6  
 7 try:
 8     conn=MySQLdb.connect(host='192.168.1.6',user='dba',passwd='111111',port=3306)
 9     cur=conn.cursor()
10      
11     #cur.execute('create database if not exists testdb')
12     conn.select_db('testdb')
13     cur.execute('create table id_info(id int,info varchar(20))')
14      
15     # value=[1,'hi rollen']
16     # cur.execute('insert into id_info values(%s,%s)',value)
17     
18     rg = 100000
19     values=[]
20     for i in range(rg):
21         values.append((i,'aaa'+str(i)))
22          
23     cur.executemany('insert into id_info values(%s,%s)',values)
24  
25     values=[]
26     for i in range(rg):
27         values.append((i+rg,'bbb'+str(i)))
28          
29     cur.executemany('insert into id_info values(%s,%s)',values)
30  
31     values=[]
32     for i in range(rg):
33         values.append((i+2*rg,'ccc'+str(i)))
34          
35     cur.executemany('insert into id_info values(%s,%s)',values)
36  
37     # cur.execute('update id_info set info="I am rollen" where id=3')
38  
39     conn.commit()
40     cur.close()
41     conn.close()
42  
43 except MySQLdb.Error,e:
44      print "Mysql Error %d: %s" % (e.args[0], e.args[1])

 经过以上代码的运行,testdb这个数据库里面就有了一个id_info表,并且这个表里面还有了300000行数据。然后是连接mysql并执行select,我比较喜欢用面向对象的方式来写代码,所以就把连接mysql的程序做了一点封装

 1 #!/usr/bin/env python
 2 
 3 # 20140105,  conn_mysql.py
 4 
 5 import MySQLdb
 6  
 7 class conn_mysql(object):
 8     def __init__(self):
 9         print "init mysql"
10 
11     def __del__(self):
12         print "quit mysql"
13 
14     def connect_db(self):
15         self.conn=MySQLdb.connect(host='192.168.1.6',user='dba',passwd='111111',db='testdb',port=3306)
16         self.cur=self.conn.cursor()
17         self.conn.select_db('testdb')
18 
19     def test_select(self):
20         count=self.cur.execute('select * from id_info')
21         print 'there has %s rows record' % count
22  
23         result=self.cur.fetchone()
24         print result
25         print 'ID: %s info %s' % result
26  
27         results=self.cur.fetchmany(5)
28         for r in results:
29             print r
30 
31         print '=='*10
32         self.cur.scroll(0,mode='absolute')
33 
34         results=self.cur.fetchall()
35         for r in results:
36             print r[1]
37  
38         self.conn.commit()
39 
40     def test_count(self, str_sql):
41         count=self.cur.execute(str_sql)
42         # print 'there has %s rows record' % count
43 
44         result=self.cur.fetchone()
45         # print 'id_info has %s rows' % result
46         str_rows = '%s' % result
47         return str_rows
48 
49     def disconnect_db(self):
50         self.cur.close()
51         self.conn.close()

test_select方法,来测试是否连接上,talbe里面数据很多,我是在只有30条数据的时候运行这个测试,之后实验中就一直是用test_count。test_count这个函数的意思是,对输入的sql,其类似格式是“select count(*) from ......”这样的时候,就把结果以字符串形式返回。下面是测试程序

 1 #!/usr/bin/env python
 2 
 3 # 20140105,  conn_mysql_raw.py
 4 
 5 import conn_mysql
 6 
 7 str_sql = 'select count(*) from id_info'
 8 
 9 db_connect = conn_mysql.conn_mysql()
10 db_connect.connect_db()
11 
12 for i in range(10000):
13     str_rows = db_connect.test_count('select count(*) from id_info where info like \'bbb%\'')
14 
15 print(str_rows + ' rows selected.')
16 
17 db_connect.disconnect_db()

 

针对之前的数据,运行10000次sql,select count(*) from id_info where info like 'bbb%',当然,每次的返回结果都是100000,主要是测试这个程序的运行时间。在我的机器上,时间是1.9s。

 然后是在mysql前面加入一层memcached,需要先下载python-memcached-latest.tar.gz,这个自行google吧,apt-get源里面似乎是没有。我拿到的版本是python-memcached-1.53。安装python-memcached之前要先安装python-setuptools,不然会报错“ImportError: No module named 'setuptools'”

tar zxvf python-memcached-latest.tar.gz
cd python-memcached-1.53/
sudo apt-get install python-setuptools
sudo python setup.py install

然后,把memcached启动,run一段python代码测试一下

1 #!/usr/bin/env python
2 # 20140105, test_memcached.py
3  
4 import memcache
5  
6 mc = memcache.Client(['localhost:11211'],debug=0)
7 mc.set("foo","bar")
8 value = mc.get("foo")
9 print value

看到输出是“bar”就说明已经连上memcached了。下面就要用memcached做mysql的缓存,看性能能提升到什么程度。先改写mysql连接的封装类

 1 #!/usr/bin/env python
 2 
 3 # 20140105,  conn_mysql.py
 4 
 5 import MySQLdb
 6 import memcache
 7 import hashlib
 8 
 9 class conn_mysql(object):
10     def __init__(self):
11         print "init mysql"
12 
13     def __del__(self):
14         print "quit mysql"
15 
16     def connect_db(self):
17         self.conn=MySQLdb.connect(host='192.168.1.6',user='dba',passwd='111111',db='testdb',port=3306)
18         self.cur=self.conn.cursor()
19         self.conn.select_db('testdb')
20 
21     def test_select(self):
22         count=self.cur.execute('select * from id_info')
23         print 'there has %s rows record' % count
24  
25         result=self.cur.fetchone()
26         print result
27         print 'ID: %s info %s' % result
28  
29         results=self.cur.fetchmany(5)
30         for r in results:
31             print r
32 
33         print '=='*10
34         self.cur.scroll(0,mode='absolute')
35 
36         results=self.cur.fetchall()
37         for r in results:
38             print r[1]
39  
40         self.conn.commit()
41 
42     def test_count(self, str_sql):
43         count=self.cur.execute(str_sql)
44         # print 'there has %s rows record' % count
45 
46         result=self.cur.fetchone()
47         # print 'id_info has %s rows' % result
48         str_rows = '%s' % result
49         return str_rows
50 
51     def connect_cache(self):
52         self.mc = memcache.Client(['localhost:11211'],debug=0)
53 
54     def test_count_cached(self, str_sql):
55         str_hash = hashlib.md5(str_sql).hexdigest()
56         #str_hash = myhash(str_sql)
57 
58         result = self.mc.get(str_hash)
59         if result != None:
60             # str_org_sql = self.mc.get('SQL'+str_hash)
61             # if str_org_sql == str_sql:
62             str_rows = '%s' % result
63             return str_rows
64 
65         count = self.cur.execute(str_sql)
66         # print 'there has %s rows record' % count
67 
68         result = self.cur.fetchone()
69         self.mc.set(str_hash, result)
70         self.mc.set('SQL'+str_hash, str_sql)
71         # print(str_hash)
72         # print 'id_info has %s rows' % result
73         str_rows = '%s' % result
74         return str_rows
75 
76     def disconnect_db(self):
77         self.cur.close()
78         self.conn.close()

增加memcached相关的配置信息,增加测试函数test_count_cached,先对输入的sql做字符串hash(我用的md5),以这个hash值为key去memcached中查找有没有结果,如果有就直接返回;否则再去mysql中查询,并把查询的结果做value,sql的hash值做key,存在memcached中。run这个测试函数

 1 #!/usr/bin/env python
 2 
 3 # 20140105,  conn_mysql_memcached.py
 4 
 5 import conn_mysql
 6 
 7 str_sql = 'select count(*) from id_info where info like \'bbb%\''
 8 
 9 
10 db_connect = conn_mysql.conn_mysql()
11 db_connect.connect_db()
12 db_connect.connect_cache()
13 
14 for i in range(10000):
15     str_rows = db_connect.test_count_cached(str_sql)
16 
17 print(str_rows + ' rows selected.')
18 
19 db_connect.disconnect_db()

经过改进之后的test_count_cached的运行时间是1.0s,改进并不如我期望的大。可能的原因,我的mysql是装在本机上的,没有网络通讯的开销,一般情况下,mysql是在单独的数据库服务器上,而memcached是在业务服务器上,做一次sql查询是有网络开销的,所以在这种场景下,效果应该会更明显。

实验中还有一个小问题,我在对比sql文本的时候只对比了hash值,并没有对比sql文本本身,如果进行这样的对比,势必会造成性能下降。事实也是如此,我加入这段对比之后,test_count_cached的运行时间变为1.8s,不考虑误差的话,运行时间基本上是刚才的case的2倍。这也很显然,因为主要的开销都是在获取memcached中的结果,加入sql文本对比的同时也多了1次获取memcached结果的消耗。