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Concept questionHard~9 min

Choose isolation for a concurrent reservation

Chooses constraints, conditional writes, optimistic conflicts, or stronger isolation to protect a limited-resource reservation without unnecessary blocking.

SQLSQL Server

Concept questionHard~9 min

Design an idempotent upsert without race conditions

Builds a race-safe upsert around database-enforced identity, explicit conflict semantics, retries, ordering, and side-effect boundaries.

SQLSQL Server

Concept questionHard~9 min

Diagnose blocking versus deadlocks

Separates a live blocking chain from a deadlock victim, gathers the right database evidence, stabilizes the incident, and fixes lock duration or access order.

SQLSQL Server

Coding problemMedium~25 min

Remove duplicate imports while keeping the newest row

Ranks duplicate import rows, previews the deletion set, and removes older copies with deterministic retention.

SQLSQL Server

Coding problemMedium~25 min

Reserve inventory with one atomic conditional update

Uses a conditional update and transaction to prevent overselling while recording the reservation consistently.

SQLSQL Server

Concept questionMedium~7 min

Use optimistic concurrency with rowversion

Prevents lost updates with an original rowversion predicate, maps zero affected rows to an explicit conflict, and defines user, retry, aggregate, and API precondition behavior.

SQLSQL Server

Concept questionMedium~7 min

Use unique constraints for business rules

Makes business uniqueness race-safe with the exact database key, while handling normalization, tenant scope, nulls, soft deletion, rollout cleanup, and stable API conflicts.

SQLSQL Server