▸case-01 I am designing a checkout endpoint in a NodeJS e-commerce application. The proposed handler opens a PostgreSQL transaction, creates an order record, issues an HTTP POST to Stripe's payment API, updates the order status to paid, and commits the transaction. Review this implementation strategy and recommend how external API side effects should be structured relative to the database transaction boundary. | pass→pass | 26,056 | 19,334 | -26% | 1 | 1 | 0% | 3,356 | 2,193 | -35% | 0 | 0 | — |
▸case-02 We have an inventory reservation transaction in PostgreSQL that suffers from serialization failures under high load. A developer suggested wrapping the entire transaction block in an automatic retry loop (up to 5 retries) whenever a 40001 serialization failure occurs. What critical safeguards must be added alongside this retry mechanism to prevent duplicate reservations? | pass→pass | 25,552 | 22,854 | -11% | 1 | 1 | 0% | 3,162 | 2,648 | -16% | 0 | 0 | — |
▸case-03 Our night-job updates 100,000 user subscription records. The developer wrapped all 100,000 updates inside a single BEGIN TRANSACTION ... COMMIT block in Python SQLAlchemy to ensure everything succeeds or fails as one giant batch. How should this batch architecture be refactored to optimize concurrency and reduce lock contention? | pass→pass | 28,403 | 20,767 | -27% | 1 | 1 | 0% | 3,224 | 2,808 | -13% | 0 | 0 | — |
▸case-04 We are building a digital wallet service where multiple concurrent microservices update user balances on PostgreSQL. We need to handle contested writes on the balance column. What specific locking strategies and retry constraints should be configured for this contested resource? | pass→pass | 25,680 | 27,160 | +6% | 1 | 1 | 0% | 3,032 | 3,804 | +25% | 0 | 0 | — |
▸case-05 When an order is placed, the backend creates an order record, writes an audit log, publishes an order_created message to RabbitMQ, and sends a confirmation email via SendGrid. Should all four operations be executed within a single database transaction block? Explain how atomic versus eventually consistent operations should be structured. | pass→pass | 20,117 | 23,113 | +15% | 1 | 1 | 0% | 2,505 | 2,952 | +18% | 0 | 0 | — |
▸case-06 A team is building a peer-to-peer money transfer endpoint. They are debating whether the unit of work should cover fetching user profiles, validating fraud rules, deducting balance from sender, adding balance to receiver, and generating a PDF receipt. How should the database transaction scope be defined for this business action? | pass→pass | 19,648 | 19,697 | +0% | 1 | 1 | 0% | 2,172 | 2,206 | +2% | 0 | 0 | — |
▸case-07 We process incoming Stripe webhooks by storing the event payload and updating order status. To handle concurrent duplicate webhooks, our team proposes a retry policy on database deadlocks. Is a retry loop alone sufficient for handling duplicate webhook payloads? | pass→pass | 20,966 | 15,717 | -25% | 1 | 1 | 0% | 2,235 | 1,806 | -19% | 0 | 0 | — |
▸case-08 In our user onboarding workflow, a single database transaction inserts a user, creates default workspace settings, calls AWS S3 API to provision storage buckets, and seeds sample data. How should this multi-step flow be restructured regarding transaction duration and external side effects? | pass→pass | 16,674 | 15,386 | -8% | 1 | 1 | 0% | 2,469 | 2,548 | +3% | 0 | 0 | — |
▸case-09 For a concert ticketing system where thousands of users attempt to reserve the same seat simultaneously, what concurrency control mechanisms, locking strategies, and retry policies need to be defined before writing the reservation service? | fail→pass | 21,715 | 23,061 | +6% | 1 | 1 | 0% | 3,329 | 3,566 | +7% | 0 | 0 | — |
▸case-10 When a user posts a product review, we save the review to PostgreSQL and update an Elasticsearch index. Should updating Elasticsearch be part of the atomic PostgreSQL transaction block? How should the system separate immediate consistency from eventual consistency? | pass→pass | 20,679 | 19,835 | -4% | 1 | 1 | 0% | 2,205 | 2,476 | +12% | 0 | 0 | — |
▸case-11 We are migrating data for a multi-tenant client with 500,000 rows across 15 tables. The proposed script wraps the entire tenant migration in a single transaction block. What are the operational risks of this transaction design, and how should it be modified? | pass→pass | 22,320 | 14,844 | -33% | 1 | 1 | 0% | 2,666 | 2,611 | -2% | 0 | 0 | — |
▸case-12 An application updates a notification record state to SENT and calls the Twilio API inside a single database transaction loop. What failure mode occurs if the database transaction aborts after Twilio sends the SMS, and how should the transaction scope be fixed? | pass→pass | 19,225 | 17,512 | -9% | 1 | 1 | 0% | 2,112 | 2,040 | -3% | 0 | 0 | — |
▸case-13 During a flash sale, item inventory drops rapidly under extreme request velocity. Design the unit of work for decrement_inventory(item_id, quantity). Where does the transaction boundary start and end, and what trade-offs must be explicitly documented? | fail→pass | 27,262 | 18,412 | -32% | 1 | 1 | 0% | 3,229 | 3,134 | -3% | 0 | 0 | — |
▸case-14 When receiving a payment status update from PayPal, a backend handler retries database updates whenever deadlocks occur. What expectation must be recorded to ensure concurrent duplicate PayPal webhooks do not result in double crediting? | pass→pass | 11,835 | 10,536 | -11% | 1 | 1 | 0% | 1,733 | 905 | -48% | 0 | 0 | — |
▸case-15 An application upgrades a user's subscription tier. It needs to charge the credit card via Chargebee, update the DB user tier, and send a welcome email. Detail the transaction boundary and compensation strategy for this operation. | pass→pass | 20,714 | 22,857 | +10% | 1 | 1 | 0% | 3,092 | 2,976 | -4% | 0 | 0 | — |
▸case-16 A legacy Rails service method performs 20 database queries, 3 external API calls, and sends 2 emails all inside an ActiveRecord::Base.transaction block. Provide actionable refactoring instructions based on transaction scoping principles. | pass→pass | 16,495 | 15,673 | -5% | 1 | 1 | 0% | 2,616 | 2,630 | +1% | 0 | 0 | — |
▸case-17 A profile update endpoint saves user metadata in MySQL and triggers asynchronous image resizing and avatar uploads to AWS S3. How should transaction scope and eventual consistency be structured for this endpoint? | pass→pass | 22,265 | 17,440 | -22% | 1 | 1 | 0% | 3,278 | 2,139 | -35% | 0 | 0 | — |
▸case-18 In an online auction system, multiple bids arrive in the same millisecond for the same item. How should the transaction body, lock expectations, and retry mechanisms be designed for high contention? | pass→pass | 24,376 | 19,479 | -20% | 1 | 1 | 0% | 3,488 | 3,174 | -9% | 0 | 0 | — |
▸case-19 When cancelling an order, a system updates order status to CANCELLED, restores inventory stock, and calls the Stripe Refund API. How should the atomic DB operations be separated from external side effects? | pass→pass | 20,685 | 15,470 | -25% | 1 | 1 | 0% | 2,506 | 2,557 | +2% | 0 | 0 | — |
▸case-20 We have a slow SELECT query joining orders and order_items on order_id with a created_at date range filter in PostgreSQL. Provide an indexing strategy to optimize this SELECT query performance. | pass→pass | 15,298 | 18,615 | +22% | 1 | 1 | 0% | 2,720 | 2,523 | -7% | 0 | 0 | — |
▸case-21 We are configuring HikariCP connection pool settings for a Java Spring Boot application running on 4 CPU cores with 50 concurrent web threads. How should we calculate and configure maximumPoolSize and minimumIdle parameters? | pass→pass | 20,500 | 19,845 | -3% | 1 | 1 | 0% | 2,503 | 2,355 | -6% | 0 | 0 | — |
▸case-22 We need to add a non-nullable status column with default value 'pending' to a 10-million row accounts table in PostgreSQL 14 without causing extended table locks. Write the DDL SQL migration statements. | pass→fail | 19,601 | 18,553 | -5% | 1 | 1 | 0% | 2,132 | 2,161 | +1% | 0 | 0 | — |
▸case-23 We need to set up point-in-time recovery (PITR) for an AWS Aurora PostgreSQL database storing financial audit logs. What backup configuration, WAL archiving parameters, and snapshot retention settings should be configured? | pass→pass | 22,388 | 26,730 | +19% | 1 | 1 | 0% | 3,560 | 3,514 | -1% | 0 | 0 | — |