数据库连接池
数据库连接池创建一批连接放到连接池,负责分配、管理和释放数据库连接,它允许应用程序重复使用一个现有的数据库连接。
原理:
连接池基本的思想是在初始化的时候,将数据库连接作为对象存储在内存中,当用户需要访问数据库时,并非建立一个新的连接,而是从连接池中取出一个已建立的空闲连接对象。使用完毕后,用户也并非将连接关闭,而是将连接放回连接池中,以供下一个请求访问使用。而连接的建立、断开都由连接池自身来管理。
DBUtils是Python的一个用于实现数据库连接池的模块。
安装:
pip3 install DBUtils
pip3 install pymysql
方式一:单例模式(文件导入db对象)
import pymysql
from DBUtils.PooledDB import PooledDB
class SqlHelper(object):
def __init__(self):
self.pool = PooledDB(
creator=pymysql, # 使用链接数据库的模块
maxconnections=6, # 连接池允许的最大连接数,0和None表示不限制连接数
mincached=2, # 初始化时,链接池中至少创建的链接,0表示不创建
blocking=True, # 连接池中如果没有可用连接后,是否阻塞等待。True,等待;False,不等待然后报错
ping=0,
# ping MySQL服务端,检查是否服务可用。# 如:0 = None = never, 1 = default = whenever it is requested, 2 = when a cursor is created, 4 = when a query is executed, 7 = always
host='127.0.0.1',
port=3306,
user='root',
password='222',
database='cmdb',
charset='utf8'
)
def open(self):
"""连接"""
conn = self.pool.connection() # 去连接池中获取一个连接
cursor = conn.cursor()
return conn,cursor
def close(self,cursor,conn):
cursor.close()
conn.close() # # 将连接放入连接池
def fetchall(self,sql, *args):
""" 获取所有数据 """
conn,cursor = self.open()
cursor.execute(sql, args)
result = cursor.fetchall() # 获取查询到的数据
self.close(conn,cursor)
return result
def fetchone(self,sql, *args):
""" 获取单条数据 """
conn, cursor = self.open()
cursor.execute(sql, args)
result = cursor.fetchone()
self.close(conn, cursor)
return result
db = SqlHelper()
方式二:单例模式(基于with上下文管理)
import pymysql
import threading
from DBUtils.PooledDB import PooledDB
"""
storage = {
1111:{'stack':[]}
}
"""
class SqlHelper(object):
def __init__(self):
self.pool = PooledDB(
creator=pymysql, # 使用链接数据库的模块
maxconnections=6, # 连接池允许的最大连接数,0和None表示不限制连接数
mincached=2, # 初始化时,链接池中至少创建的链接,0表示不创建
blocking=True, # 连接池中如果没有可用连接后,是否阻塞等待。True,等待;False,不等待然后报错
ping=0,
# ping MySQL服务端,检查是否服务可用。# 如:0 = None = never, 1 = default = whenever it is requested, 2 = when a cursor is created, 4 = when a query is executed, 7 = always
host='127.0.0.1',
port=3306,
user='root',
password='222',
database='cmdb',
charset='utf8'
)
self.local = threading.local()
def open(self):
conn = self.pool.connection()
cursor = conn.cursor()
return conn, cursor
def close(self, cursor, conn):
cursor.close()
conn.close()
def fetchall(self, sql, *args):
""" 获取所有数据 """
conn, cursor = self.open()
cursor.execute(sql, args)
result = cursor.fetchall() # 获取查询到的数据
self.close(conn, cursor)
return result
def fetchone(self, sql, *args):
""" 获取单条数据 """
conn, cursor = self.open()
cursor.execute(sql, args)
result = cursor.fetchone()
self.close(conn, cursor)
return result
def __enter__(self):
conn,cursor = self.open()
rv = getattr(self.local,'stack',None)
if not rv:
self.local.stack = [(conn,cursor),]
else:
rv.append((conn,cursor))
self.local.stack = rv
return cursor
def __exit__(self, exc_type, exc_val, exc_tb):
rv = getattr(self.local,'stack',None)
if not rv:
# del self.local.stack
return
conn,cursor = self.local.stack.pop()
cursor.close()
conn.close()
db = SqlHelper()
使用:
from sqlhelper import db
# db.fetchall(...)
# db.fetchone(...)
with db as c1:
c1.execute('select * from ...')
with db as c2:
c1.execute('select * from ...')
print(123)
方式三:较简单
import pymysql
import threading
from DBUtils.PooledDB import PooledDB
POOL = PooledDB(
creator=pymysql, # 使用链接数据库的模块
maxconnections=6, # 连接池允许的最大连接数,0和None表示不限制连接数
mincached=2, # 初始化时,链接池中至少创建的链接,0表示不创建
blocking=True, # 连接池中如果没有可用连接后,是否阻塞等待。True,等待;False,不等待然后报错
ping=0,
# ping MySQL服务端,检查是否服务可用。# 如:0 = None = never, 1 = default = whenever it is requested, 2 = when a cursor is created, 4 = when a query is executed, 7 = always
host='127.0.0.1',
port=3306,
user='root',
password='222',
database='cmdb',
charset='utf8'
)
class SqlHelper(object):
def __init__(self):
self.conn = None
self.cursor = None
def open(self):
conn = POOL.connection()
cursor = conn.cursor()
return conn, cursor
def close(self):
self.cursor.close()
self.conn.close()
def __enter__(self):
self.conn,self.cursor = self.open()
return self.cursor
def __exit__(self, exc_type, exc_val, exc_tb):
self.close()
使用:
with SqlHelper() as c1:
c1.execute('select 1')
with SqlHelper() as c2:
c2.execute('select 2')
print(666)
with SqlHelper() as cursor:
cursor.execute('select 1')
with SqlHelper() as cursor:
cursor.execute('select 1')