python - Python mysql（使用pymysql）自动重新连接

Question

我不确定这是否可能，但我正在寻找一种在连接丢失时重新连接到 mysql 数据库的方法。所有连接都保存在 gevent 队列中，但我认为这无关紧要。我敢肯定，如果我花一些时间，我可以想出一种重新连接到数据库的方法。但是，我浏览了 pymysql 代码，发现 Connection 类中有一个“ping”方法，我不确定如何使用。

该方法看起来会第一次重新连接，但之后它再次将重新连接标志切换为 False？我可以使用这种方法吗，或者如果连接丢失，是否有不同的方法来建立连接？即使不是 pymysql，人们如何解决数据库服务器宕机而不得不重新建立与 mysql 服务器的连接？

def ping(self, reconnect=True):
    ''' Check if the server is alive '''
    if self.socket is None:
        if reconnect:
            self._connect()
            reconnect = False
        else:
            raise Error("Already closed")
    try:
        self._execute_command(COM_PING, "")
        return self._read_ok_packet()
    except Exception:
        if reconnect:
            self._connect()
            return self.ping(False)
        else:
            raise

score 14 · Accepted Answer

终于找到了一个可行的解决方案，可能会对某人有所帮助。

from gevent import monkey
monkey.patch_socket()
import logging

import gevent
from gevent.queue import Queue
import pymysql as db

logging.basicConfig(level=logging.DEBUG)
LOGGER = logging.getLogger("connection_pool")


class ConnectionPool:
    def __init__(self, db_config, time_to_sleep=30, test_run=False):
        self.username = db_config.get('user')
        self.password = db_config.get('password')
        self.host = db_config.get('host')
        self.port = int(db_config.get('port'))
        self.max_pool_size = 20
        self.test_run = test_run
        self.pool = None
        self.time_to_sleep = time_to_sleep
        self._initialize_pool()

    def get_initialized_connection_pool(self):
        return self.pool

    def _initialize_pool(self):
        self.pool = Queue(maxsize=self.max_pool_size)
        current_pool_size = self.pool.qsize()
        if current_pool_size < self.max_pool_size:  # this is a redundant check, can be removed
            for _ in xrange(0, self.max_pool_size - current_pool_size):
                try:
                    conn = db.connect(host=self.host,
                                      user=self.username,
                                      passwd=self.password,
                                      port=self.port)
                    self.pool.put_nowait(conn)

                except db.OperationalError, e:
                    LOGGER.error("Cannot initialize connection pool - retrying in {} seconds".format(self.time_to_sleep))
                    LOGGER.exception(e)
                    break
        self._check_for_connection_loss()

    def _re_initialize_pool(self):
        gevent.sleep(self.time_to_sleep)
        self._initialize_pool()

    def _check_for_connection_loss(self):
        while True:
            conn = None
            if self.pool.qsize() > 0:
                conn = self.pool.get()

            if not self._ping(conn):
                if self.test_run:
                    self.port = 3306

                self._re_initialize_pool()

            else:
                self.pool.put_nowait(conn)

            if self.test_run:
                break
            gevent.sleep(self.time_to_sleep)

    def _ping(self, conn):
        try:
            if conn is None:
                conn = db.connect(host=self.host,
                                  user=self.username,
                                  passwd=self.password,
                                  port=self.port)
            cursor = conn.cursor()
            cursor.execute('select 1;')
            LOGGER.debug(cursor.fetchall())
            return True

        except db.OperationalError, e:
            LOGGER.warn('Cannot connect to mysql - retrying in {} seconds'.format(self.time_to_sleep))
            LOGGER.exception(e)
            return False

# test (pytest compatible) -------------------------------------------------------------------------------------------
import logging

from src.py.ConnectionPool import ConnectionPool

logging.basicConfig(level=logging.DEBUG)
LOGGER = logging.getLogger("test_connection_pool")


def test_get_initialized_connection_pool():
    config = {
        'user': 'root',
        'password': '',
        'host': '127.0.0.1',
        'port': 3305
    }
    conn_pool = ConnectionPool(config, time_to_sleep=5, test_run=True)
    pool = conn_pool.get_initialized_connection_pool()
    # when in test run the port will be switched back to 3306
    # so the queue size should be 20 - will be nice to work 
    # around this rather than test_run hack
    assert pool.qsize() == 20

score 13 · Accepted Answer

好吧，我在我的应用程序中遇到了同样的问题，我在PyMySQL 文档上找到了一个方法，它可以 ping 到服务器并检查连接是否关闭，如果它已关闭，则它会再次重新连接。

from pymysql import connect
from pymysql.cursors import DictCursor

# create the connection
connection = connect(host='host', port='port', user='user', 
                     password='password', db='db', 
                     cursorclass=DictCursor)

# get the cursor
cursor = connection.cursor()

# if the connection was lost, then it reconnects
connection.ping(reconnect=True)      

# execute the query
cursor.execute(query)

我希望它有所帮助。

score 2 · Accepted Answer

最简单的方法是在发送查询之前检查连接。

您可以通过创建一个包含两个方法的小类来做到这一点：connect和query：

import pymysql
import pymysql.cursors

class DB:
    def connect(self):
        self.conn = pymysql.connect(
                             host=hostname,
                             user=username,
                             password=password,
                             db=dbname,
                             charset='utf8mb4',
                             cursorclass=pymysql.cursors.DictCursor,
                             port=3306)

    def query(self, sql):
        try:
            cursor = self.conn.cursor()
            cursor.execute(sql)
        except pymysql.OperationalError:
            self.connect()
            cursor = self.conn.cursor()
            cursor.execute(sql)
        return cursor

db = DB()

现在，每当您使用请求发送查询时，都会db.query("example SQL")自动准备遇到连接错误，并self.connect()在需要时重新连接。

请记住：这是一个简化的示例。通常，您希望让 PyMySQL 帮助您转义查询中的特殊字符。为此，您必须在query方法中添加第二个参数并从那里开始。

score 1 · Accepted Answer

旧的，但我在访问程序中的托管数据库时遇到了类似的问题。我最终使用的解决方案是创建一个装饰器，以便在进行查询时自动重新连接。

给定一个连接函数：

def connect(self):
    self.conn = mysql.connector.connect(host=self.host, user=self.user, 
    database=self.database, password=self.password)
    self.cursor = self.conn.cursor()
    print("Established connectionn...")

我建立

def _reconnect(func):
    @wraps(func)
    def rec(self,*args,**kwargs):
        try:
            result = func(self,*args,**kwargs)
            return result
        except (mysql.connector.Error, mysql.connector.Warning) as e:
            self.connect()
            result = func(self,*args,**kwargs)
            return result
    return rec

这样任何使用连接的函数现在都可以这样装饰

@_reconnect
def check_user_exists(self,user_id):
    self.cursor.execute("SELECT COUNT(*) FROM _ where user_id={};".format(user_id))
    if self.cursor.fetchall()[0][0]==0:
        return False 
    else:
        return True

此装饰器将重新建立连接并重新运行任何涉及到数据库查询的函数。

score 1 · Accepted Answer

逻辑很简单，如果连接关闭然后尝试重新连接几次，在这种情况下我使用最大尝试 15 次重新连接或 ping。

import pymysql, pymysql.cursors
conn = pymysql.connect(
                         host=hostname,
                         user=username,
                         password=password,
                         db=dbname,
                         charset='utf8mb4',
                         cursorclass=pymysql.cursors.DictCursor,
                         )
cursor = conn.cursor()
# you can do transactions to database and when you need conn later, just make sure the server is still connected
if conn.open is False:
   max_try = 15
   try = 0
   while conn.open is False:
       if try < max_try:
           conn.ping() # autoreconnect is true by default
       try +=1

# check the conn again to make sure it connected
if conn.open:
    # statements when conn is successfully reconnect to the server
else:
    # it must be something wrong : server, network etc

python - Python mysql（使用pymysql）自动重新连接

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