Python mysql (using pymysql) auto reconnect

Question

I\'m not sure if this is possible, but I\'m looking for a way to reconnect to mysql database when the connection is lost. All the connections are held in a gevent queue but that

Answer 1

Finally got a working solution, might help someone.

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