python - SQLAlchemy 错误 MySQL 服务器已经消失

Question

错误 OperationalError: (OperationalError) (2006, 'MySQL server has gone away') 我在 Flask 上编写项目时已经收到此错误，但我不明白为什么会收到此错误.

我有这样的代码(是的，如果代码小且执行速度快，那么没有错误)\

db_engine = create_engine('mysql://root@127.0.0.1/mind?charset=utf8', pool_size=10, pool_recycle=7200)
Base.metadata.create_all(db_engine)

Session = sessionmaker(bind=db_engine, autoflush=True)
Session = scoped_session(Session)
session = Session()

# there many classes and functions

session.close()

这段代码给我返回错误'MySQL server has gone away'，但是一段时间后，当我在我的脚本中使用暂停时返回它。

我从 openserver.ru 使用 Mysql(它是 web 服务器，例如 wamp)。

谢谢..

Answer 1

SQLAlchemy 现在有一篇关于如何使用 ping 对连接的新鲜度持悲观态度的精彩文章:

http://docs.sqlalchemy.org/en/latest/core/pooling.html#disconnect-handling-pessimistic

从那里开始，

from sqlalchemy import exc
from sqlalchemy import event
from sqlalchemy.pool import Pool

@event.listens_for(Pool, "checkout")
def ping_connection(dbapi_connection, connection_record, connection_proxy):
    cursor = dbapi_connection.cursor()
    try:
        cursor.execute("SELECT 1")
    except:
        # optional - dispose the whole pool
        # instead of invalidating one at a time
        # connection_proxy._pool.dispose()

        # raise DisconnectionError - pool will try
        # connecting again up to three times before raising.
        raise exc.DisconnectionError()
    cursor.close()

并进行测试以确保上述工作正常:

from sqlalchemy import create_engine
e = create_engine("mysql://scott:tiger@localhost/test", echo_pool=True)
c1 = e.connect()
c2 = e.connect()
c3 = e.connect()
c1.close()
c2.close()
c3.close()

# pool size is now three.

print "Restart the server"
raw_input()

for i in xrange(10):
    c = e.connect()
    print c.execute("select 1").fetchall()
    c.close()