Start by clarifying requirements and scale, then design a data model and API for core operations (create account, deposit, transfer). For ranking by outgoing transaction volume, propose an efficient data structure like a balanced BST or skip list that supports incremental updates and ordered retrieval, and discuss trade-offs with simpler approaches like periodic sorting.
Pro tip: Demonstrate awareness of real-world constraints: mention idempotency for transfers, transaction isolation levels, and how you'd handle hot accounts (e.g., sharding or caching) to avoid bottlenecks.
Ask about expected throughput, consistency needs, and whether ranking is real-time or batch. Define functional and non-functional requirements.
Define entities (Account, Transaction) and operations (createAccount, deposit, transfer, getRankedAccounts). Specify fields, types, and relationships.
Describe how to handle deposits and transfers with atomicity and consistency, using transactions or locks. Discuss error handling and idempotency.
Propose a data structure (e.g., balanced BST, skip list, or sorted set) to maintain accounts ordered by outgoing volume, supporting O(log n) updates and O(log n + k) retrieval.
Compare real-time ranking vs. batch processing, and discuss scaling strategies like sharding, caching, and eventual consistency.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying requirements and constraints, then propose a design that separates the immediate debit from the scheduled credit using a persistent job queue or scheduler. Emphasize idempotency, exactly-once processing, and how to handle late or missed executions to ensure balance consistency.
Pro tip: Discuss how you would handle scheduler failures and ensure exactly-once credit, perhaps using a transactional outbox pattern or idempotent credit operations with unique payment IDs. This shows you think about real-world reliability beyond the happy path.
Ask about expected scale, latency requirements, consistency guarantees, and failure handling. Confirm that the 24-hour delay is exact and that cashback must be credited even if the system restarts.
Define a Payment entity with unique ID, account ID, amount, timestamp, and status (e.g., PENDING_CASHBACK, COMPLETED). Also consider a separate CashbackSchedule table or queue entry with due time and payment ID.
Atomically debit the account and create a scheduled job for the cashback credit. Use a transaction to ensure both happen or neither. Return the payment ID to the client.
Use a reliable scheduler (e.g., database-backed job queue, delayed message queue) that triggers at the due time. The job credits the account and marks the payment as completed, ensuring idempotency via the payment ID.
For any operation after the due time, the balance must include the cashback. This can be achieved by having the scheduler update the balance promptly, or by computing balance on read as stored balance plus pending cashbacks whose due time has passed.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Mostly straightforward once the scheduling structure was in place.
Start by clarifying the API contract: define the endpoint, request parameters (account ID, payment ID), and response schema (status: pending/received, plus error codes). Then outline the implementation: validate inputs, query the payment/cashback store, map internal states to the API response, and handle errors with appropriate HTTP status codes and messages. Emphasize idempotency, security, and observability.
Pro tip: Mention that you would return a 404 for invalid account or payment ID, but avoid leaking whether the account exists if the requester is not authorized—use 403 or 404 consistently to prevent enumeration attacks. Also, consider adding a `Retry-After` header for pending statuses to guide clients.
Specify the endpoint (e.g., GET /accounts/{accountId}/payments/{paymentId}/cashback-status), request parameters, and response body with fields like `status` (PENDING, RECEIVED) and `receivedAt` timestamp. Include error responses for 400, 404, 403, and 500.
Check that accountId and paymentId are present and well-formed (e.g., UUIDs). Authenticate the request and verify the caller has access to the account; return 401/403 if not.
Fetch the payment record by paymentId and ensure it belongs to the given accountId. Then retrieve the associated cashback record, which may be in a separate table or service. Use efficient queries with proper indexes.
Translate the internal cashback status (e.g., PENDING, PROCESSED, FAILED) to the API's status values. If received, include the timestamp; if pending, optionally include an estimated date.
Return 404 if the payment or account does not exist, or if the payment does not belong to the account. For invalid IDs, return 400. Log errors and monitor for anomalies. Ensure the endpoint is idempotent and cacheable if appropriate.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.