18

I am doing a lot of inserts to a mysql table in a short period of time from python code (using pymysql) that uses a lot of different threads.

Each thread, of which there are many, may or may not end up pushing data to a MySql table.

Here is the code block that causes the issue (this can be called for each thread running):

        sql = ("INSERT INTO LOCATIONS (location_id, place_name) VALUES (%s, %s)")
        cursor = self.connection.cursor()          
        cursor.execute(sql, (location_id, place_name))     
        cursor.close()

and it is specifically this line:

cursor.execute(sql, (location_id, place_name))

That causes this error:

pymysql.err.InterfaceError: (0, '')

Note also that i define self.connection in the init of the class the above block is in. so all threads share a self.connection object but get their own cursor object.

The error seems to happen randomly and only starts appearing (I think) after doing quite a few inserts into the mysql table. It is NOT consistent meaning it does not happen with every single attempt to insert into mysql.

I have googled this specific error and it seems like it could be from the cursor being closed before running the query. but i believe it is obvious i am closing the cursor after the query is executed.

Right now I think this is happening either because of:

  1. Some sort of write limit to the MySql table, although the error of pymysql.err.InterfaceError doesn't seem to say this specifically
  2. The fact that I have a connection defined at a high scope that is having cursors created from in threads could somehow be causing this problem.

Thoughts?

sometimesiwritecode
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6 Answers6

18

seems like the issue was related to me having a universal connection object. creating one per thread seems to have removed this issue.

sometimesiwritecode
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11

I get the same problem. There is a global connection in my project code, and I find that this connection will be timed out if there is no mysql operation for a long time. This error will occur when execute sql tasks, because of the timed-out connection.

My solution is: reconnecting mysql before execute sql tasks.

sql = ("INSERT INTO LOCATIONS (location_id, place_name) VALUES (%s, %s)")
self.connection.ping()  # reconnecting mysql
with self.connection.cursor() as cursor:         
    cursor.execute(sql, (location_id, place_name))
InSync
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DavidLin3
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3

After upgrading to a newer PyMySQL version, I was suddenly getting the same error, but without doing a lot of queries. I was also getting an additional error:

[..]
pymysql.err.InterfaceError: (0, '')

During handling of the above exception, another exception occurred:

pymysql.err.Error: Already closed

Since this appears to be only real place where this error is being discussed, I'll post my solution here too.

Per the PyMySQL documentation, I was doing this:

connection = pymysql.connect([...])

with connection:
    with connection.cursor() as cursor:
        [..]
        cursor.execute(sql)

# lots of other code

with connection:
    [...]

What I failed to notice is that with connection will automatically close the connection to the database when that context manager finished executing. So subsequent queries would fail, even though I was still able to get a cursor from the connection without error.

The solution was to not use the with connection context manager, but closing the database connection manually:

connection = pymysql.connect([...])

with connection.cursor() as cursor:
    [..]
    cursor.execute(sql)

# lots of other code

with connection.cursor() as cursor:
    [..]

connection.close()
Ferry Boender
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2

I've got the same error, than i found that pymysql is threadsafe, so you need to open an connection for every thread as @sometimesiwritecode said.

Source found: https://github.com/PyMySQL/PyMySQL/issues/422

Bordotti
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1

dont close the connection remove the cursor.close() line should continue update your database

Kuda William Rukuni
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0

For pymysql its essential to call either the connection.ping() or the cursor.connection.ping() methods to be able to continue using the connection otherwise it closes. ping() re-establishes the connection with the db/cluster and depending on whether you are trying to connect to an AWS RDS cluster you might need to pass in an argument to reconnect set to a boolean True value:

  • connection.ping(reconnect=True) or
  • cursor.connection.ping(reconnect=True)

This is right before consecutive execute() calls. Doesnt hurt to put before every execute to make sure not to fall into the same error.

Wiam Nasr
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