What is a Data Sync?

Sync can run in one direction (a source of truth pushes changes out to read-only copies) or bidirectionally, where either system can originate a change and both need to reconcile it - bidirectional sync is meaningfully harder because it has to resolve conflicts when the same record is edited in both places before the last sync completed. Sync mechanisms range from full-refresh (re-pulling everything on a schedule, simple but wasteful) to incremental (only pulling records changed since the last sync, using timestamps or change-data-capture) to real-time (event-driven, propagating a change the moment it happens via webhooks or streams). The choice trades off freshness against cost and complexity. A sync system needs a clear conflict-resolution rule - last-write-wins, source-system-priority, or manual review for high-stakes conflicts - because without one, two systems disagreeing about the current state of a record is a matter of when, not if, especially once more than two systems are kept in sync with each other.