How to check if a MySQL connection is open in Python?

问题

I am using MySQLdb (http://mysql-python.sourceforge.net/). It seems that connection.open and connection.sqlstate() do not work for me. Below is the code:

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

But when I ran "sudo service mysql stop; sleep 60; sudo service mysql start;" to do the testing. The output is as following. It seems that the following piece of output repeated for ever (I killed the process finally). When the server is down, connection.open is 1 and connection.sqlstate() is 00000. But when server is up, connection.executemany() still throw exceptions. Any ideas? Thanks.

...
    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
...

UPDATE

I tested again. The output is as following. each sleep is 10 seconds. The output is OK except the connection.open is 1 even when server is down. But connection.sqlstate() is right (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.

回答1:

Try this-

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"

回答2:

I have been searching for this solution for some time and I couldn't find an elegant solution.

It seems there isn't a direct way of doing that. You will only find out your connection is closed if you try to execute a query.

I end up doing something similar to this answer: How to check the connection alive in python?

回答3:

you should code like this: at every execute before , ping the mysql-server,for example

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()

回答4:

Just in case anyone finds this helpful:

import socket
import time
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
while sock.connect_ex(('db', 3306)) != 0: # 'db' is the host, 3306 is the port
    print('MySQL is not ready yet.')
    time.sleep(2)
sock.close()
print("Now it's up and running! Bye!")

来源：https://stackoverflow.com/questions/33239480/how-to-check-if-a-mysql-connection-is-open-in-python

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python

mysql

mysql-python