Background Sync Template for Product Managers

Use a combination of delta sync and full sync fallback. When the app comes to foreground, request changes since `lastSyncTimestamp`. If the delta is too large (server returns a "full sync required" response) or the timestamp is older than your retention window, trigger a full re-sync. Design the full re-sync to be incremental so it does not block the UI. The user should see their most recent data within seconds while older data loads in the background.

Use WebSockets when you need sub-second latency for collaborative features (shared editing, chat, live dashboards). Use polling when data freshness requirements are minutes, not seconds. WebSockets add connection management complexity and consume more battery on mobile due to keep-alive packets. Many apps use a hybrid approach: WebSockets while the app is in the foreground, and push notifications plus on-foreground pull for background sync.

Build a sync test harness that simulates multiple devices making concurrent changes with varying network conditions. Key scenarios to automate: 1000+ offline edits syncing at once, concurrent edits to the same record from 5+ devices, and network interruption mid-sync. Measure sync completion time, conflict rate, and data integrity (checksums match across all devices after sync settles). The [beta testing plan template](/templates/beta-testing-plan-template) covers how to structure a beta program that captures real-world sync failures from diverse network environments.

It depends on your data freshness requirements and battery budget. For most apps, 15-30 minutes in the background is sufficient. iOS will schedule BGAppRefreshTask at system-optimal times regardless of your requested interval. Android's WorkManager respects a 15-minute minimum for periodic work. In the foreground, poll every 30-60 seconds if WebSocket is not an option. Always make the interval configurable server-side so you can adjust without an app update.