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Best Practices

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Overview

Practice Description Impact
Keep handlers fast Event handlers execute synchronously, so keep them fast Performance
Handle errors Implement error handling in event handlers Reliability
Use parallel processing Enable parallel processing for independent events Performance
Limit concurrency Set appropriate max_concurrent_event_handlers based on resources Resource management
Idempotency Make event handlers idempotent when possible Reliability
Logging Log important events for debugging and monitoring Observability

Performance Considerations

Event handlers execute synchronously in the request context. Keep them fast to avoid blocking the main request flow.

Parallel Processing

Enable parallel event processing for independent events to improve performance. Set concurrent_event_handle_enable=True and configure max_concurrent_event_handlers.

Event handling in python-cqrs:

  • Runtime Processing — Events are processed synchronously in the same request context
  • Automatic Dispatch — Events are automatically dispatched to registered handlers
  • Parallel Support — Multiple events can be processed in parallel with configurable limits
  • Two Types — DomainEvent (in-process) and NotificationEvent (message broker)
  • Side Effects — Event handlers perform side effects without blocking command execution

Use event handlers to implement side effects like notifications, read model updates, and workflow triggers while keeping your command handlers focused on business logic.