Key takeaway
Atomic writes, isolation anomalies, locks, uniqueness constraints, and invariant protection. Start with the related games below when you want to turn the definition into practice.
Why this matters
Correct backend systems protect business invariants even when requests race.
How to practice
Practice deciding when a lock, constraint, transaction, or idempotency key is required.
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Learning objectives
- Identify common concurrency anomalies such as lost updates, phantoms, and partial writes.
- Choose between row locks, atomic updates, constraints, serializable isolation, and optimistic concurrency.
- Explain why application-level checks are not enough for many shared data invariants.
- Own invariants in service transactions.
- Fetch JPA data for the required response shape.
- Make rollback and configuration behavior explicit.
Common mistakes to avoid
- Checking a condition in application code and writing later without a lock or constraint.
- Using last-write-wins where users expect conflict detection.
- Assuming READ COMMITTED prevents every race.
- Adding broad table locks where row locks, constraints, or snapshots would be safer.
- Starting independent repository transactions.
- Solving N plus one with a larger pool.
Games for Transactions & Consistency
Start with the first game, then use local review history to revisit missed decisions.
Databases Advanced
Defend database invariants from concurrent requests by choosing transactions, locks, constraints, snapshot reads, and optimistic concurrency.
- Time
- 7-10 minutes
- Concept
- Database transactions, isolation anomalies, locks, and invariant protection
- Data & Performance
- Database Reliability
- SQL
- transactions
- isolation
Play Transaction Isolation Arena Spring Advanced
Place Spring transactions, JPA fetch plans, rollback rules, and validated configuration at production boundaries.
- Time
- 9-11 minutes
- Concept
- Spring transaction and data boundaries
- Spring Production
- Transactions
- SQL Indexes
- Spring
Play Spring Data Boundary Clinic Reliability Intermediate
Diagnose retry scenarios and choose safe idempotency behavior for payments, emails, imports, orders, PUT updates, and scarce inventory.
- Time
- 6-9 minutes
- Concept
- Idempotency, retries, duplicate prevention, and consistency
- Production Reliability
- Async Workflows
- Idempotency
- Reliability
- Consistency
Play Idempotency Key Clinic Databases Intermediate
Choose the best database index for simplified schemas and queries while learning full scans, covering indexes, sort avoidance, and composite order.
- Time
- 7-10 minutes
- Concept
- Database indexing and query performance
- Data & Performance
- Algorithmic Reasoning
- SQL
- indexes
- performance
Play SQL Index Quest