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Python数据库连接池DBUtils详解

时间:2021-07-01 10:21:17 帮助过:4人阅读

Python数据库连接池DBUtils详解

what‘s the DBUtils

  DBUtils 是一套用于管理数据库连接池的Python包,为高频度高并发的数据库访问提供更好的性能,可以自动管理连接对象的创建和释放。并允许对非线程安全的数据库接口进行线程安全包装。

DBUtils提供两种外部接口:

  • PersistentDB :提供线程专用的数据库连接,并自动管理连接。
  • PooledDB :提供线程间可共享的数据库连接,并自动管理连接。

实测证明 PersistentDB 的速度是最高的,但是在某些特殊情况下,数据库的连接过程可能异常缓慢,而此时的PooledDB则可以提供相对来说平均连接时间比较短的管理方式。

另外,实际使用的数据库驱动也有所依赖,比如SQLite数据库只能使用PersistentDB作连接池。 下载地址:http://www.webwareforpython.org/downloads/DBUtils/

DBUtils使用方法

  连接池对象只初始化一次,一般可以作为模块级代码来确保。 PersistentDB的连接例子:

import DBUtils.PersistentDB 
persist=DBUtils.PersistentDB.PersistentDB(dbpai=MySQLdb,maxusage=1000,**kwargs)

  这里的参数dbpai指使用的底层数据库模块,兼容DB-API的。maxusage则为一个连接最大使用次数,参考了官方例子。后面的**kwargs则为实际传递给MySQLdb的参数。

  获取连接: conn=persist.connection() 实际编程中用过的连接直接关闭 conn.close() 即可将连接交还给连接池。

PooledDB使用方法同PersistentDB,只是参数有所不同。

  • dbapi :数据库接口
  • mincached :启动时开启的空连接数量
  • maxcached :连接池最大可用连接数量
  • maxshared :连接池最大可共享连接数量
  • maxconnections :最大允许连接数量
  • blocking :达到最大数量时是否阻塞
  • maxusage :单个连接最大复用次数
  • setsession :用于传递到数据库的准备会话,如 [”set name UTF-8″] 。
db=pooled.connection()
cur=db.cursor()
cur.execute(sql)
res=cur.fetchone()
cur.close() # or del cur
db.close() # or del db

python不用连接池的MySQL连接方法

import MySQLdb
conn= MySQLdb.connect(host=‘localhost‘,user=‘root‘,passwd=‘pwd‘,db=‘myDB‘,port=3306)  
#import pymysql
#conn = pymysql.connect(host=‘localhost‘, port=‘3306‘, db=‘game‘, user=‘root‘, password=‘123456‘, charset=‘utf8‘)
cur=conn.cursor()
SQL="select * from table1"
r=cur.execute(SQL)
r=cur.fetchall()
cur.close()
conn.close()

用连接池后的连接方法

import MySQLdb
from DBUtils.PooledDB import PooledDB
pool = PooledDB(MySQLdb,5,host=‘localhost‘,user=‘root‘,passwd=‘pwd‘,db=‘myDB‘,port=3306) #5为连接池里的最少连接数

conn = pool.connection()  #以后每次需要数据库连接就是用connection()函数获取连接就好了
cur=conn.cursor()
SQL="select * from table1"
r=cur.execute(SQL)
r=cur.fetchall()
cur.close()
conn.close()

DBUtils下载地址:https://pypi.python.org/pypi/DBUtils/

import sys
import threading
import MySQLdb
import DBUtils.PooledDB

connargs = { "host":"localhost", "user":"user1", "passwd":"123456", "db":"test" }
def test(conn):
    try:
        cursor = conn.cursor()
        count = cursor.execute("select * from users")
        rows = cursor.fetchall()
        for r in rows: pass
    finally:
        conn.close()
        
def testloop():
    print ("testloop")
    for i in range(1000):
        conn = MySQLdb.connect(**connargs)
        test(conn)
        
def testpool():
    print ("testpool")
    pooled = DBUtils.PooledDB.PooledDB(MySQLdb, **connargs)
    for i in range(1000):
        conn = pooled.connection()
        test(conn)
        
def main():
    t = testloop if len(sys.argv) == 1 else testpool
    for i in range(10):
        threading.Thread(target = t).start()
        
if __name__ == "__main__":
    main()

看看 10 线程的测试结果。

$ time ./main.py  
testloop  
testloop  
testloop  
testloop  
testloop  
testloop  
testloop  
testloop  
testloop  
testloop  
real    0m4.471s  
user    0m0.570s  
sys     0m4.670s  
$ time ./main.py -l  
testpool  
testpool  
testpool  
testpool  
testpool  
testpool  
testpool  
testpool  
testpool  
testpool  
real    0m2.637s  
user    0m0.320s  
sys     0m2.750s  

  虽然测试方式不是很严谨,但从测试结果还是能感受到 DBUtils 带来的性能提升。当然,我们我们也可以在 testloop() 中一直重复使用一个不关闭的 Connection,但这却不适合实际开发时的情形。

DBUtils 提供了几个参数,便于我们更好地调整资源利用。

DBUtils.PooledDB.PooledDB(self, creator,   
    mincached=0, maxcached=0, maxshared=0, maxconnections=0, blocking=False, maxusage=None,   
    setsession=None, failures=None, *args, **kwargs)  
Docstring:  
    Set up the DB-API 2 connection pool.  
    creator: either an arbitrary function returning new DB-API 2  
        connection objects or a DB-API 2 compliant database module  
    mincached: initial number of idle connections in the pool  
        (0 means no connections are made at startup)  
    maxcached: maximum number of idle connections in the pool  
        (0 or None means unlimited pool size)  
    maxshared: maximum number of shared connections  
        (0 or None means all connections are dedicated)  
        When this maximum number is reached, connections are  
        shared if they have been requested as shareable.  
    maxconnections: maximum number of connections generally allowed  
        (0 or None means an arbitrary number of connections)  
    blocking: determines behavior when exceeding the maximum  
        (if this is set to true, block and wait until the number of  
        connections decreases, otherwise an error will be reported)  
    maxusage: maximum number of reuses of a single connection  
        (0 or None means unlimited reuse)  
        When this maximum usage number of the connection is reached,  
        the connection is automatically reset (closed and reopened).  
    setsession: optional list of SQL commands that may serve to prepare  
        the session, e.g. ["set datestyle to ...", "set time zone ..."]  
    failures: an optional exception class or a tuple of exception classes  
        for which the connection failover mechanism shall be applied,  
        if the default (OperationalError, InternalError) is not adequate  
    args, kwargs: the parameters that shall be passed to the creator  
        function or the connection constructor of the DB-API 2 module  

DBUtils 仅提供给了连接池管理,实际的数据库操作依然是由符合 DB-API 2 标准的目标数据库模块完成的。

一个面向对象使用DBUtils的栗子

# coding=utf-8
"""
使用DBUtils数据库连接池中的连接,操作数据库
OperationalError: (2006, ‘MySQL server has gone away’)
"""
import json
import pymysql
import datetime
from DBUtils.PooledDB import PooledDB
import pymysql


class MysqlClient(object):
    __pool = None;

    def __init__(self, mincached=10, maxcached=20, maxshared=10, maxconnections=200, blocking=True,
                 maxusage=100, setsession=None, reset=True,
                 host=‘127.0.0.1‘, port=3306, db=‘test‘,
                 user=‘root‘, passwd=‘123456‘, charset=‘utf8mb4‘):
        """

        :param mincached:连接池中空闲连接的初始数量
        :param maxcached:连接池中空闲连接的最大数量
        :param maxshared:共享连接的最大数量
        :param maxconnections:创建连接池的最大数量
        :param blocking:超过最大连接数量时候的表现,为True等待连接数量下降,为false直接报错处理
        :param maxusage:单个连接的最大重复使用次数
        :param setsession:optional list of SQL commands that may serve to prepare
            the session, e.g. ["set datestyle to ...", "set time zone ..."]
        :param reset:how connections should be reset when returned to the pool
            (False or None to rollback transcations started with begin(),
            True to always issue a rollback for safety‘s sake)
        :param host:数据库ip地址
        :param port:数据库端口
        :param db:库名
        :param user:用户名
        :param passwd:密码
        :param charset:字符编码
        """

        if not self.__pool:
            self.__class__.__pool = PooledDB(pymysql,
                                             mincached, maxcached,
                                             maxshared, maxconnections, blocking,
                                             maxusage, setsession, reset,
                                             host=host, port=port, db=db,
                                             user=user, passwd=passwd,
                                             charset=charset,
                                             cursorclass=pymysql.cursors.DictCursor
                                             )
        self._conn = None
        self._cursor = None
        self.__get_conn()

    def __get_conn(self):
        self._conn = self.__pool.connection();
        self._cursor = self._conn.cursor();

    def close(self):
        try:
            self._cursor.close()
            self._conn.close()
        except Exception as e:
            print e

    def __execute(self, sql, param=()):
        count = self._cursor.execute(sql, param)
        print count
        return count

    @staticmethod
    def __dict_datetime_obj_to_str(result_dict):
        """把字典里面的datatime对象转成字符串,使json转换不出错"""
        if result_dict:
            result_replace = {k: v.__str__() for k, v in result_dict.items() if isinstance(v, datetime.datetime)}
            result_dict.update(result_replace)
        return result_dict

    def select_one(self, sql, param=()):
        """查询单个结果"""
        count = self.__execute(sql, param)
        result = self._cursor.fetchone()
        """:type result:dict"""
        result = self.__dict_datetime_obj_to_str(result)
        return count, result

    def select_many(self, sql, param=()):
        """
        查询多个结果
        :param sql: qsl语句
        :param param: sql参数
        :return: 结果数量和查询结果集
        """
        count = self.__execute(sql, param)
        result = self._cursor.fetchall()
        """:type result:list"""
        [self.__dict_datetime_obj_to_str(row_dict) for row_dict in result]
        return count, result

    def execute(self, sql, param=()):
        count = self.__execute(sql, param)
        return count

    def begin(self):
        """开启事务"""
        self._conn.autocommit(0)

    def end(self, option=‘commit‘):
        """结束事务"""
        if option == ‘commit‘:
            self._conn.autocommit()
        else:
            self._conn.rollback()


if __name__ == "__main__":
    mc = MysqlClient()
    sql1 = ‘SELECT * FROM shiji  WHERE  id = 1‘
    result1 = mc.select_one(sql1)
    print json.dumps(result1[1], ensure_ascii=False)

    sql2 = ‘SELECT * FROM shiji  WHERE  id IN (%s,%s,%s)‘
    param = (2, 3, 4)
    print json.dumps(mc.select_many(sql2, param)[1], ensure_ascii=False)

Python数据库连接池DBUtils详解

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