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Architecture, data, networking, and sync interviews

Pattern comparisons​

MVC/MVP/MVVM/MVI describe responsibility/state/event organization, not complete architectures. Compare state complexity, lifecycle, testability, team vocabulary and ceremony. Clean Architecture protects business policy through dependency direction; it does not require a use-case class for every repository call.

UI -> presentation/domain contracts -> repositories
                              implementations -> local/network

Explain source of truth, ownership and data flow before layer names.

Data questions​

Repository: mediates domain data and sources; it is not merely a Retrofit forwarding wrapper. Define freshness, cache, errors, concurrency and writes.

Room transaction: protects a local atomic invariant; it does not make server/local distributed work atomic. Use idempotent commands/outbox/reconciliation.

DataStore: typed/preferences small durable state; not relational query/large datasets. SQLite/Room for structured relationships/transactions.

Paging: UI consumes PagingData; local source plus RemoteMediator can provide offline truth. Remote keys, refresh/append errors, duplicates and invalidation require explicit design.

Networking/sync questions​

Define timeouts by phase/operation, cancellation, retryable errors, exponential backoff/jitter, idempotency, auth refresh serialization, pagination, error body, serialization compatibility and observability. Retrying POST is safe only with protocol/idempotency design.

Offline-first means local readable state plus durable user intent, sync state/conflict policy, freshness UX and reconciliation. Last-write-wins is only valid when domain consequences permit it.

Design drills​

  1. Cache-first product page with stale-while-revalidate and explicit error/freshness UI.
  2. Offline edit from two devices: version/precondition, conflict response, merge or user choice.
  3. Token expiry for 100 parallel calls: one refresh, queued callers, failure/logout and no recursive interceptor loop.
  4. Database migration across five released schemas with large data/disk pressure and forward repair.

Red flags​

  • ❌ “Single source of truth means only one physical source.”
  • ✅ one authoritative model per context; data can synchronize from several systems.
  • ❌ “Exactly once sync.”
  • ✅ at-least-once attempts plus idempotency/deduplication/reconciliation.