如何在Python中检查MySQL连接是否打开？

Question

我正在使用MySQLdb（http://mysql-python.sourceforge.net/）。似乎connection.open和connection.sqlstate（）对我不起作用。下面是代码：

def open(self):
    #TODO: check the connection's status
    # self.__conn.open OR self.__conn.sqlstate()
    try:
        print "sqlstate:"+str( self.__conn.sqlstate() )
        print "open?"+str( self.__conn.open )
        return "00000" == self.__conn.sqlstate()
    except Exception as e:
        print "Exception while checking MYSQL Connection:"+str(e) 
        return False

但是当我运行“sudo service mysql stop；sleep 60；sudo service mysql start；”来做测试时。输出如下。下面的输出似乎永远重复（我最终终止了这个过程）。当服务器关闭时，connection.open为1，connection.sqlstate（）为00000。但当服务器启动时，connection.executemany（）仍然抛出异常。有什么想法吗？谢谢。

...
    2015-10-20 14:09:06 Exception while executing statement:(2006, 'MySQL server has gone away')
    2015-10-20 14:09:06 sqlstate:00000
    2015-10-20 14:09:06 open?1
    2015-10-20 14:09:06 Reconnected to MYSQL.
    2015-10-20 14:09:06 Exception while executing statement:(2006, 'MySQL server has gone away')
    2015-10-20 14:09:06 sqlstate:00000
    2015-10-20 14:09:06 open?1
    2015-10-20 14:09:06 Reconnected to MYSQL.
    2015-10-20 14:09:06 Exception while executing statement:(2006, 'MySQL server has gone away')
    2015-10-20 14:09:06 sqlstate:00000
    2015-10-20 14:09:06 open?1
    2015-10-20 14:09:06 Reconnected to MYSQL.
    2015-10-20 14:09:06 Exception while executing statement:(2006, 'MySQL server has gone away')
    2015-10-20 14:09:06 sqlstate:00000
    2015-10-20 14:09:06 open?1
...

更新

我又测试了一次。输出如下。每次睡眠10秒。除了connection.open是1，即使服务器关闭，输出也正常。但是connection.sqlstate（）是正确的（HY000）。

 2015-10-20 14:35:56 Exception while executing statement:(2006, 'MySQL server has gone away')
2015-10-20 14:35:56 Exception while ping:(2003, "Can't connect to MySQL server on '10.1.1.25' (111)")
2015-10-20 14:35:56 sqlstate:HY000
2015-10-20 14:35:56 open?1
2015-10-20 14:35:56 sleeping...
2015-10-20 14:36:06 Exception while ping:(2003, "Can't connect to MySQL server on '10.1.1.25' (111)")
2015-10-20 14:36:06 sqlstate:HY000
2015-10-20 14:36:06 open?1
2015-10-20 14:36:06 sleeping...
2015-10-20 14:36:16 Exception while ping:(2003, "Can't connect to MySQL server on '10.1.1.25' (111)")
2015-10-20 14:36:16 sqlstate:HY000
2015-10-20 14:36:16 open?1
2015-10-20 14:36:16 sleeping...
2015-10-20 14:36:26 Exception while ping:(2003, "Can't connect to MySQL server on '10.1.1.25' (111)")
2015-10-20 14:36:26 sqlstate:HY000
2015-10-20 14:36:26 open?1
2015-10-20 14:36:26 sleeping...
2015-10-20 14:36:36 Exception while ping:(2003, "Can't connect to MySQL server on '10.1.1.25' (111)")
2015-10-20 14:36:36 sqlstate:HY000
2015-10-20 14:36:36 open?1
2015-10-20 14:36:36 sleeping...
2015-10-20 14:36:46 Exception while ping:(2003, "Can't connect to MySQL server on '10.1.1.25' (111)")
2015-10-20 14:36:46 sqlstate:HY000
2015-10-20 14:36:46 open?1
2015-10-20 14:36:46 sleeping...
2015-10-20 14:36:56 Exception while ping:(2003, "Can't connect to MySQL server on '10.1.1.25' (111)")
2015-10-20 14:36:56 sqlstate:HY000
2015-10-20 14:36:56 open?1
2015-10-20 14:36:56 sleeping...
2015-10-20 14:37:06 sqlstate:00000
2015-10-20 14:37:06 open?1
2015-10-20 14:37:06 Reconnected to MYSQL.

Answer 1

你应该这样编码： 在每次执行之前，ping mysql服务器，例如

import MySQLdb as db
    class DB(object):
        def __init__(self):
            try:
                self.conn =mdb.connect(host='***',port=3306,user='',passwd='')
            if (self.conn):
                INFO_LOG("DB init success")
            else:
                INFO_LOG("DB init fail")
            self.conn.autocommit(True)
            self.conn.select_db(DB_NAME)
            self.cursor = self.conn.cursor()
        except Exception as e:
            CRITICAL_LOG("DB init fail %s " % str(e))
    def insert(self,player_id,cmd):
        try:
            if self.conn is None:
                self.__init__()
            else:
                self.conn.ping(True)
            self.cursor.execute('INSERT INTO table values("%s",%s")' %
            (player_id,cmd))
        except Exception as e:
            import traceback
            traceback.print_exc()
            #error ocurs,rollback
            self.conn.rollback()

Answer 2

我已经寻找这个解决方案一段时间了，我找不到一个优雅的解决方案。

似乎没有直接的办法。只有在尝试执行查询时，您才会发现连接已关闭。

最后我做了类似于这个答案的事情： How to check the connection alive in python?

Answer 3

试试这个-

import MySQLdb

def main():
  # Connect to the MySQL database
  db = MySQLdb.connect(host = 'z.cs.utexas.edu', user = 'userName', passwd = 'password', db = 'dbName')

  # Check if connection was successful
  if (db):
    # Carry out normal procedure
    print "Connection successful"
  else:
    # Terminate
    print "Connection unsuccessful"