Upgrading a Django version or an idle Django shell session has brought about an unexpected challenge: intermittent OperationalError: (2006, 'MySQL server has gone away') messages for long-running scripts. These scripts sometimes experience extended periods without communicating with the database, leading to connection timeouts. Previously, Django would automatically re-establish the connection, but this behavior seems to have changed with the upgrade.
The Issue: Connection Timeout
The core issue lies in the connection timeout, particularly with scripts that involve phases of inactivity lasting several minutes. Before the upgrade, Django handled reconnections seamlessly, but now it requires manual intervention. This change has led to frequent script failures, disrupting the workflow.
Potential Fixes and Workarounds
1. Understanding the Change
This issue might be related to a change implemented in Django 1.7, as outlined in Django ticket 21463. The ticket suggests that Django’s behavior in handling database connections has been altered, potentially impacting long-running scripts.
2. Manual Connection Management
A practical solution is to manually manage the database connections by using the close_old_connections() method. This method ensures that any stale connections are closed, and new ones are established as needed.
Example:
import django.db
# Close old connections
django.db.close_old_connections()
# Your long-running task code hereWhile the Django documentation for version 1.9 does not explicitly mention close_old_connections(), you can refer to its implementation in the Django codebase on GitHub.
3. Background Processes
For background processes such as rqworker, which execute separate jobs, the issue persists if there are no user actions for a duration exceeding the wait_timeout setting in MySQL. Despite setting CONN_MAX_AGE to a value less than wait_timeout, the problem remains because Django only checks connections before and after each request.
To address this, you can incorporate the close_old_connections() method in your background jobs to ensure a fresh connection is available for each task.
Example for rqworker:
from django.db import close_old_connections
def job_function():
close_old_connections()
# Job code here
close_old_connections()This approach aligns with the per-request connection handling strategy in Django, ensuring that connections are validated and refreshed as needed.
4. Idle Django Shell Sessions
Another scenario where this error occurs is during idle Django shell sessions. If a shell session remains idle for an extended period (e.g., over 48 hours), attempting a database operation can result in the same OperationalError.
Quick Fix:
import django.db
django.db.close_old_connections()Running this command in your shell session will close any old connections and establish a new one, preventing the OperationalError.
Conclusion
Upgrading to Django 1.7 introduces changes in how database connections are managed, impacting long-running scripts, background processes, and idle Django shell sessions. By manually managing connections using the close_old_connections() method, you can mitigate OperationalError: (2006, 'MySQL server has gone away') issues and ensure your scripts run smoothly.
For further details on this issue and potential fixes, you can refer to the following resources:
By implementing these solutions, you can maintain the stability and reliability of your Django applications post-upgrade.
