SQLAlchemy/MySQL Lost connection to MySQL server during query

问题

SQLAlchemy (0.9.8) and mysql-5.6.21-osx10.8-x86_64 and MAC OS X 10.3.3 (Yosemite)

I keep getting intermittent:

InterfaceError: (InterfaceError) 2013: Lost connection to MySQL server during query u'SELECT..... '

I have read up a few thread and most cases are resolved by adding this to my.cnf

   max_allowed_packet = 1024M

which should be more than big enough for what I tried to do. After doing this, I step hit it intermittently. And putting this line in /etc/my.cnf:

   log-error = "/Users/<myname>/tmp/mysql.err.log"
   log-warnings = 3

I am hoping to get more details, but all I see is something like this:

   [Warning] Aborted connection 444 to db: 'dbname' user: 'root' host: 'localhost' (Got an error reading communication packets)

I have reached a point where i think more detail better logging may help, or if there's something else i could try before this.

Thanks.

回答1:

looks like your MySQL connection is timing out after a long period of inactivity, I bet it won't happen if you're constantly querying your DB with existing settings. There are couple of settings on both MySQL and sql sides which should resolve this issue:

check your SQLa engine's pool_recycle value, try different / smaller value, e.g. 1800 (secs). If you're reading DB settings from file, set it as

pool_recycle: 1800

otherwise specify it during engine init, e.g.

from sqlalchemy import create_engine
e = create_engine("mysql://user:pass@localhost/db", pool_recycle=1800)

check / modify your wait_timeout MySQL variable, see https://dev.mysql.com/doc/refman/5.6/en/server-system-variables.html#sysvar_wait_timeout which is the number of seconds the server waits for activity on a noninteractive connection before closing it. e.g.

show global variables like 'wait_timeout';

find a combination that works for your environment.

回答2:

Based on suggestions from this, this and many other articles on the internet, wrapping all my functions with the following decorator helped me resolve the "Lost Connection" issue with mariadb as the backend db. Please note that db below is an instance of flask_sqlalchemy.SQLAlchemy, but the concept will remain the same for an sqlalchemy session too.

def manage_session(f):
    def inner(*args, **kwargs):

        # MANUAL PRE PING
        try:
            db.session.execute("SELECT 1;")
            db.session.commit()
        except:
            db.session.rollback()
        finally:
            db.session.close()

        # SESSION COMMIT, ROLLBACK, CLOSE
        try:
            res = f(*args, **kwargs)
            db.session.commit()
            return res
        except Exception as e:
            db.session.rollback()
            raise e
            # OR return traceback.format_exc()
        finally:
            db.session.close()
    return inner

I also added pool_recycle of 50 seconds in Flask SQLAlchemy config, but that didnt visibly contribute to the solution.

EDIT1:

Below is a sample snippet of how it was used in the final code:

from flask_restful import Resource

class DataAPI(Resource):

    @manage_session
    def get(self):
        # Get data rows from DB

来源：https://stackoverflow.com/questions/29755228/sqlalchemy-mysql-lost-connection-to-mysql-server-during-query

标签

python

mysql

macos

sqlalchemy