Python SQLAlchemy-“ MySQL服务器已消失”

发布于 2021-01-29 16:04:20

让我们看看下一个片段-

@event.listens_for(Pool, "checkout")
def check_connection(dbapi_con, con_record, con_proxy):

cursor = dbapi_con.cursor()
try:
    cursor.execute("SELECT 1")  # could also be dbapi_con.ping(),
                                # not sure what is better
except exc.OperationalError, ex:
    if ex.args[0] in (2006,   # MySQL server has gone away
                      2013,   # Lost connection to MySQL server during query
                      2055):  # Lost connection to MySQL server at '%s', system error: %d
        # caught by pool, which will retry with a new connection
        raise exc.DisconnectionError()
    else:
        raise


engine = create_engine('mysql://user:puss123@10.0.51.5/dbname', pool_recycle = 3600,pool_size=10, listeners=[check_connection])

session_factory = sessionmaker(bind = engine, autoflush=True, autocommit=False)
db_session = session_factory()

...
some code that may take several hours to run
...

db_session.execute('SELECT * FROM ' + P_TABLE + " WHERE id = '%s'" % id)

我以为在checkout事件下注册checkout_connection函数可以解决该问题,但现在没有问题了,我该如何告诉SQLAlchemy处理连接丢失,因此每次我调用execute()时,它都会检查连接是否可用,如果不可用,会再次启动它吗?

-—更新----

SQLAlchemy的版本是0.7.4

-—更新----

def checkout_listener(dbapi_con, con_record, con_proxy):
    try:
        try:
            dbapi_con.ping(False)
        except TypeError:
            dbapi_con.ping()
    except dbapi_con.OperationalError as exc:
        if exc.args[0] in (2006, 2013, 2014, 2045, 2055):
            raise DisconnectionError()
        else:
            raise


engine = create_engine(CONNECTION_URI, pool_recycle = 3600,pool_size=10)
event.listen(engine, 'checkout', checkout_listener)
session_factory = sessionmaker(bind = engine, autoflush=True, autocommit=False)
db_session = session_factory()

session_factory发送到每个新创建的线程

class IncidentProcessor(threading.Thread):

    def __init__(self, queue, session_factory):
        if not isinstance(queue, Queue.Queue):
            raise TypeError, "first argument should be of %s" (type(Queue.Queue))
        self.queue = queue
        self.db_session = scoped_session(session_factory)
        threading.Thread.__init__(self)

    def run(self):

    self.db_session().execute('SELECT * FROM ...')

    ...
        some code that takes alot of time
    ...

    self.db_session().execute('SELECT * FROM ...')

现在,当很长一段时间后执行运行时,出现“ MySQL服务器已消失”错误

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1 个回答
  • 面试哥
    面试哥 2021-01-29
    为面试而生,有面试问题,就找面试哥。

    对此进行了讨论,该文档很好地描述了该问题,因此我使用了他们推荐的方法来处理此类错误:http : //discorporate.us/jek/talks/SQLAlchemy-
    EuroPython2010.pdf

    看起来像这样:

    from sqlalchemy import create_engine, event
    from sqlalchemy.exc import DisconnectionError
    
    
    def checkout_listener(dbapi_con, con_record, con_proxy):
        try:
            try:
                dbapi_con.ping(False)
            except TypeError:
                dbapi_con.ping()
        except dbapi_con.OperationalError as exc:
            if exc.args[0] in (2006, 2013, 2014, 2045, 2055):
                raise DisconnectionError()
            else:
                raise
    
    
    db_engine = create_engine(DATABASE_CONNECTION_INFO,
                              pool_size=100,
                              pool_recycle=3600)
    event.listen(db_engine, 'checkout', checkout_listener)
    


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