SQLAlchemy error MySQL server has gone away

Question

Error OperationalError: (OperationalError) (2006, \'MySQL server has gone away\') i\'m already received this error when i coded project on Flask, but i cant underst

Answer 1

SQLAlchemy now has a great write-up on how you can use pinging to be pessimistic about your connection's freshness:

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

From there,

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()

And a test to make sure the above works:

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()