Python的SQLAlchemy的 - “MySQL服务器消失”

Question

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)   

我认为结账事件下注册checkout_connection功能将解决它，但它现在didnt 的问题我是如何告诉SQLAlchemy处理连接丢失的，所以每次我调用execute（）它都会检查连接是否可用，如果不是，它会再次启动它？

---- ---- UPDATE

的SQLAlchemy的版本是0.7.4

---- ---- UPDATE

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 ...') 

现在当时间的大周期我得到的“MySQL服务器消失”错误

Answer 1

有一说起这个，还有这个文档描述的问题非常好听，所以我用他们推荐的方法来处理这样的错误：http://discorporate.us/jek/talks/SQLAlchemy-EuroPython2010.pdf

它看起来是这样的：

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) 

Answer 2

后执行的运行后，可以尝试这样的事情：

while True: 
    try: 
     db_session.execute('SELECT * FROM ' + PONY_TABLE + " WHERE id = '%s'" % incident_id) 
     break 
    except SQLAlchemyError: 
     db_session.rollback() 

如果连接消失，这将举一个例外，会议将是rollback d，它会再试一次很可能会成功。

Answer 3

尝试pool_recycle参数为create_engine。

从the documentation：

Connection Timeouts

MySQL features an automatic connection close behavior, for connections that have been idle for eight hours or more. To circumvent having this issue, use the pool_recycle option which controls the maximum age of any connection:

engine = create_engine('mysql+mysqldb://...', pool_recycle=3600)