Python mysql(使用pymysql)自动重新连接

Question

我不确定这是否可行,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,我可以想出一种方法来重新连接到数据库.但是我看了一下pymysql代码,我看到Connection类中有一个'ping'方法,我不确定如何使用它.

该方法看起来会在第一次重新连接,但之后又将重新连接标志再次切换为False？我可以使用这种方法,还是有不同的方法来建立连接丢失？即使不是pymysql,人们如何处理,数据库服务器崩溃并且不得不重新建立与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

Answer 1

终于得到了一个有效的解决方案

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

Answer 2

好吧，我在我的应用程序中遇到了同样的问题，我在PyMySQL 文档中找到了一种方法，该方法可以 ping 服务器并检查连接是否已关闭，如果已关闭，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)

我希望它有帮助。