Leveraging Flink to Detect User Sessions and Engage DoorDash Consumers with Real-Time Notifications

DoorDash was sending cart abandonment notifications to users who were still actively browsing. The result? Annoying customers and missing conversion opportunities.

The DoorDash team rebuilt their notification system using Apache Flink for real-time session detection. Instead of blindly polling backend services, they now track actual user activity through mobile and web events to send smarter, timely notifications.

Key Takeaways

• 6x faster notification send speeds by detecting real user inactivity
• 40% higher send-to-open rate and 2.6% boost in visit rates
• Flink manages hundreds of gigabytes of state tracking hour-long user sessions
• Frontend events enable detection impossible with backend data alone
• Configuration-driven pipeline makes adding new notification types trivial

The team shares hard-won lessons about working with frontend events, including why some events arrived 24 hours late.