Django Connection Pooling with psycopg Issues

Based on the error you're experiencing with Django's new connection pooling feature in Django 5.1, there are several considerations to address the connection stability issues you're facing with django-q2 workers.

Understanding the Issue

The error message indicates that the connection pool is discarding closed or bad connections, which suggests there might be issues with how connections are being maintained or recycled in your long-running django-q2 worker processes.

Potential Solutions

1. Configure Connection Pool Parameters

Instead of using the simple pool: True configuration, you might need to provide specific parameters to the ConnectionPool:

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DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.postgresql",
        # ...
        "OPTIONS": {
            "pool": {
                "min_size": 5,
                "max_size": 20,
                "timeout": 30,  # Connection timeout in seconds
                "reconnect": True,
                "max_lifetime": 1800,  # Max connection lifetime in seconds (30 minutes)
            },
        },
    },
}

2. Consider CONN_MAX_AGE Setting

For long-running processes like django-q2 workers, you might need to adjust the CONN_MAX_AGE setting:

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DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.postgresql",
        "CONN_MAX_AGE": 300,  # 5 minutes
        # ...
        "OPTIONS": {
            "pool": {...},
        },
    },
}

3. Handle Connection Cleanup

For long-running processes outside Django's request-response cycle (like django-q2 workers), connections might remain open until explicitly closed. You might need to periodically call:

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from django.db import close_old_connections

# Call this periodically in your worker process
close_old_connections()

4. Thread Considerations

Since each thread maintains its own connection, ensure your database can support the number of simultaneous connections required by your worker threads. The error "sorry too many clients already" suggests you might be hitting connection limits.

Additional Considerations

1. The "lost synchronization with server" error often indicates network issues or connection interruptions between your application and the PostgreSQL server.

2. For django-q2 specifically, you might need to adjust how it manages database connections, as it might not be fully compatible with Django's connection pooling implementation.

3. Check if there are any network timeouts or firewall rules that might be causing connections to drop unexpectedly.

4. Consider implementing connection health checks in your application to detect and handle bad connections proactively.

Since this is a new feature in Django 5.1, you might also want to check for any reported issues in the Django issue tracker related to connection pooling with long-running processes or django-q2 specifically.