Amey-Thakur Realtime data sync
Most realtime features are not collaborative editing but live data: a dashboard, a list, a status that must not go stale. The failure mode is quiet drift, where the client believes something the server stopped believing an hour ago.
Method
- Subscribe narrowly. Push only what this client is displaying, because broad subscriptions waste bandwidth and leak data the user should not receive (see realtime-permissions).
- Send deltas with a sequence number. Changes rather than whole payloads, numbered so the client can detect a gap rather than silently missing one.
- Resync on gap or reconnect. Detecting a missed sequence triggers a full refresh of that resource, which is the only reliable recovery from divergence.
- Reconcile push with fetch. Data arriving by subscription and by request must merge under one rule, or the two paths overwrite each other in ways that depend on timing.
- Bound what the client holds. Live subscriptions accumulate state in long-lived sessions, so eviction is part of the design rather than an afterthought.
- Coalesce high-frequency updates. Rendering every change to a fast moving value wastes the frame budget; batch to the refresh rate the user can perceive (see batching-and-debouncing).
- Show staleness when the connection drops. An interface that looks live while disconnected is actively misleading, particularly for operational data.
Boundaries
- Push keeps data fresh; it does not guarantee delivery, so periodic reconciliation remains necessary.
- Realtime for data that changes rarely is usually unjustified complexity over simple polling.
- Ordering guarantees come from your protocol rather than the transport (see delivery-guarantees).