PostgreSQL Interview Questions for 5 Years Experience

PostgreSQL Interview Questions for 5 Years Experience Work through these 12 questions out loud. Open any question for the full model answer, the trap to avoid, and the follow-up a panel usually asks.

  1. What are text blocks and how do they improve Java code?

    String query = """ SELECT u.id, u.name FROM users u WHERE u.active = true """; — readable without \n concatenation. Use formatted for parameters carefully — prefer...

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  2. Best practices for Spring Data pagination with Pageable?

    Controller: @PageableDefault(size=20, sort="createdAt", direction=DESC) Pageable p. Cap size at 100. Admin reports: keyset pagination on id > lastId for deep pages — OFFSET...

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  3. Saga pattern — choreography vs orchestration?

    Order saga: reserve inventory → charge payment → ship. Failure at payment triggers release inventory compensation. Orchestration clearer for complex flows with visibility....

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  4. Explain the transactional outbox pattern.

    OrderService @Transactional saves Order and OutboxEvent(type=ORDER_CREATED, payload=json). OutboxProcessor @Scheduled polls FOR UPDATE SKIP LOCKED, sends to Kafka, updates...

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  5. Database sharding strategies for high-scale Java services?

    Shard by tenant_id mod 32 — RoutingDataSource lookup. User-scoped queries single shard. Global admin reports from CQRS read replica or Elasticsearch. Plan shard key early —...

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  6. How does @Transactional work?

    Spring creates a proxy around @Transactional beans. Calling createOrder() from another bean starts a transaction on the thread-bound EntityManager; commit on success, rollback...

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  7. How do you test Spring Boot applications?

    Unit test services with Mockito — no Spring. @WebMvcTest + MockMvc for controller contract. @DataJpaTest for repository queries. @SpringBootTest + Testcontainers for critical...

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  8. How do Spring application events work with @EventListener?

    OrderService publishes OrderCreatedEvent after save. EmailListener @EventListener sends confirmation. @TransactionalEventListener(AFTER_COMMIT) prevents email on rolled-back...

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  9. When use @Query native SQL vs JPQL in Spring Data JPA?

    JPQL for standard entity fetches and portable logic. Native for PostgreSQL-specific jsonb queries, recursive CTEs, or performance-tuned index hints after EXPLAIN. Interface...

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  10. How do Flyway/Liquibase integrate with Spring Boot JPA?

    Prod: spring.jpa.hibernate.ddl-auto=validate, Flyway V1__init.sql through Vn. CI: @Testcontainers PostgreSQL + Flyway migrate + integration tests. Never rename column without...

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  11. A REST API is slow only in production, not locally. How do you debug it?

    Enable Micrometer timers and Hibernate statistics or datasource-proxy in staging with prod-like data. Check Hikari `connections-active`, JVM GC pauses, and Feign/RestClient...

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  12. What is the difference between ArrayList and LinkedList?

    ArrayList: dynamic array, great for get(i) and iteration, amortized append. LinkedList: node chain, costly random access, only wins for frequent insert/remove in middle with...

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